Eight legs, two fangs and an attitude
Frequently feared, but mostly misunderstood, spiders have a dazzling repertoire of behaviour, and engineering skills which are unmatched in the animal world.
Margaret is 30. She is a successful medical practitioner, but she has a problem. She has arachnophobia. She can’t bear to look at, let alone touch, a spider—even a photograph of a spider. Sometimes at night she has to turn on the light with something other than her hand, for fear that a spider could be sitting on the switch, ready to pounce.
When she and her husband moved into a new house which had been vacant for some time, she had to put on a hat before she could face vacuuming up all the spiders’ webs. She used the longest extension pipes she could find, and tried to vacuum the rooms without leaving the hallway.
“I couldn’t live in Australia, and I certainly couldn’t live within a hundred miles of Sydney,” she says. She once had a holiday in Sydney where she heard stories about the highly venomous funnel web spider’s habit of living near swimming pools, especially in the guttering around the edges. So, whenever she swam laps she turned three feet short of the ends, afraid that if she put her hand up on the tiles a waiting spider would rear up on its hind legs and plunge its fangs into her. Her worst nightmare is of being put into a glass tank full of poisonous spiders—a stunt actually performed in a Sydney shopping mall, which she read about in the paper, with horror.
Margaret doesn’t know why she’s so afraid of spiders, but she “hates their shape, their legs and the way they scuttle”. She finds that her phobia, which is worst when life is stressful, is best dealt with “using Black Flag—half a can per spider”.
While Margaret’s abhorrence of spiders may be extreme, it is not uncommon—among animal phobias, fear of spiders is second only to fear of snakes. For most of us, it starts with our parents’ reaction to them—or perhaps being teased by siblings or playmates—and is reinforced by nursery rhymes, myths and spiders playing bad-guy roles at the movies—as in the recent film Arachnophobia.
Some spider-haters attribute their revulsion to the fear of being bitten; others mention the spider’s hairiness, the low-slung body, the ability to remain motionless for long periods, then dart out to seize prey. One Auckland entomologist (who, ironically, has no difficulty handling a weta or praying mantis) says, “It’s definitely the legs—the way a spider puts them down so softly and deliberately when it walks, as if it’s feeling its way. The thought of those stroking legs on my body gives me the creeps!”
One person who has no such qualms is Grace Hall, a spider taxonomist with the Mt Albert branch of the Department of Scientific and Industrial Research. While I’m waiting in the DSIR’s reception area to see her, I notice a middle-aged woman clutching an Agee jar with a greaseproof paper lid and a jumble of leaves and twigs inside. After a few minutes, Grace emerges from a corridor and spots the Agee jar. Smiling, soothing, she asks where the spider was found. Was it on the ground or on vegetation? Was there a web? Deftly, she flips off the lid . . . the woman takes an involuntary step backwards. Grace is probing around inside the jar with her finger, making reassuring noises about this being “probably one of the sheetweb spiders, but I’ll have to have a good look at it under the microscope” and “thanks for bringing it in.”
It’s all part of the job. Along with fellow-researcher Trevor Crosby, Grace Hall fields the telephone calls and visits of Aucklanders curious to know what eight-legged wonder they have discovered on their citrus tree or in their woodshed. Occasionally, she has to deal with true arachnophobics—those for whom spiders are the devil incarnate. Soon after she arrived at the DSIR she received a call from a petrified mother who had discovered a spider in the bath, and who told Grace she was not moving until someone got it out of there.
“The poor woman was still in her dressing gown, with her children clustered around her,” recalls Grace. “I picked up the spider and took it away. It was large, but, of course, quite harmless.”
One of Grace Hall’s special interests is the Avondale spider, which lives in the next suburb along from Mt Albert, and virtually nowhere else in Auckland, or, for that matter, the country. Avondale spiders were in the news recently: they were chosen to star in the movie Arachnophobia. The film required large, fearsome-looking spiders that could run fast and scale walls. Tarantulas, the preferred choice for arachnovillains, would have been too heavy for wall-climbing, and the DSIR won the contract to supply 370 Avondales, at $30 apiece.
At an out-of-the-way spot near a stream, Grace Hall approaches a grove of loose-barked wattle trees. Selecting a likely-looking tree, she pulls back a piece of bark that has cracked and curled in the sun. No luck. She clambers around the bank and finds another promising hideaway. She levers back the bark . . . and this time she finds a spider tucked into the tightest of tight recesses, where the bark and the trunk are almost one. It scuttles to an edge, hesitates momentarily in the bright sunlight, then leaps off into the surrounding vegetation and disappears.
Finally, she finds what she is looking for: a colony—perhaps 50 young Avondale spiders huddled together with their mother, flattening themselves against the timber and looking not at all frightening. In fact, these small pinkish creatures look rather cute as they try to shuffle away, like crabs uncovered in a rock pool.
The crab analogy is not inappropriate, given the spider’s Latin name, Delena cancerides, and the fact that it is one of a group known as giant crab spiders, named for their flattened appearance and spread-out legs—adaptations which allow them to hide under bark or beneath stones.
The Avondale, or huntsman, spider is not a native species, but, like the wattle trees it likes to live on, an immigrant from Australia. The spider arrived here 70 years ago in a packet of timber bound for the Avondale racetrack or railway station—depending on whom vou talk to. In all that time, the spider has spread to just a few places in the suburb. and neighbouring Blockhouse Bay. New Lynn and Mt Albert—probably because it’s so fussy about its habitat. By contrast, many of our immigrants. once acclimatised, have become widely established.
Any Avondales that do roam, sometimes turning up on bedroom ceilings and frightening the life out of the occupants, tend to be males searching for mates; females seldom wander from the colonies.
In addition to their large size (up to 20cm with legs extended) and longevity (up to three years for a female), it is their communal behaviour that sets the Avondales apart. Young spiders will often live in a colony of around 200, with maybe half a dozen mature spiders, until they’re almost adult themselves. The night-hunting Avondales often share food, with up to 10 spiders feeding on prey one of them has caught. This behaviour is most unusual for a hunting spider— indeed, for any spider, for almost all are strictly solitary. The only other social spiders are those which build large, communal webs (in India, these spiders sometimes build enormous, three-dimensional structures which cloak whole groves of trees) and live together in their hundreds, or even thousands.
In recent years, fewer Avondale spider sightings have been reported, and Grace Hall is sure that the population is in decline. “As more and more bush is cleared, the colonies cannot sustain themselves,” she says. “If the trend continues, I can see a time when there won’t be any left.”
Unlike their screen persona, Avondale spiders are neither dangerous nor vindictive—they make great pets! Perhaps it is ironic that the DSIR should procure such harmless spiders for Hollywood to portray as ruthless and deadly fiends—but Spielberg and Co. would have made the movie anyway, and the DSIR has made the most of the heightened public awareness of spiders by helping put together a spider roadshow to do a bit of positive spider PR around the country. Naturally, the Avondale is the star of this show, too, though putting in a more honest performance.
When last heard of, the eight-legged movie stars, still in the USA, were enjoying a comfortable retirement at a place called “Spider Pharm”, an establishment which researches snake and spider venom.
As children, we are taught that spiders have eight legs while insects have six. But the number eight comes up in other aspects of spider biology: most spiders have eight eyes, and their bodies have a roughly figure-of-eight shape, for, unlike insects, their body pattern consists of two segments, not three. The typical head and thorax of insects are fused to form the cephalothorax in spiders. A narrow waist, the pedicel, connects this frontal section to the abdomen.
Like insects, spiders have an external skeleton—a waterproof suit of armour which protects the soft internal organs from damage and desiccation, and to which the muscles are attached on the inside. The thickness of the skeleton varies, from very thin at movable joints to very thick at the top and front of the head. The abdomen is also fairly thinly clad, allowing it to expand after a heavy meal or, in females, as the eggs develop.
Like insects and all other arthropods (such as crabs, crayfish, millipedes and slaters), spiders must periodically shed their exoskeleton in order to grow. Six or more moults will usually be required to reach adulthood, but the number varies according to the size of the spider.
Moulting is a traumatic experience that involves shedding the entire outer skin as well as some of the internal linings of the gut and breathing apparatus. Web-building spiders carry out this process while suspended from a silk thread. Exhausted from the effort of freeing first the cephalothorax, then the legs, jaws, palps and finally the abdomen from its old outfit, the spider hangs limply, flexing its legs now and then to ensure they will have full mobility when the new armour hardens off.
Spiders belong to a class of invertebrates called arachnids, a group which also contains scorpions, ticks, mites and harvestmen (creatures which have their head, thorax and abdomen fused into a single unit). While not nearly as numerous as insects (which are conservatively estimated to number more than 10 million species) spiders have adapted to virtually every ecological niche, from the mountains to the sea, from tree tops to underground burrows. New Zealand even has a spider which makes its home between the tides, often living in the crevices created by clumps of oysters. A European species does one better and lives exclusively under water in a silken “diving bell”.
The bodies of the smallest spiders are less than half a millimetre across, while giant tarantulas, the Hulk Hogans of the spider world, have 10cm-long bodies and are able to capture small birds.
Spiders are the lions and tigers of the arthropods—there is not a vegetarian amongst them. They make their living by stalking or trapping their victims, subduing them with venom injected through hollow fangs, dissolving their soft tissues with powerful digestive juices and then sucking out their liquid lunch.
Their preferred prey is insects, and wherever insects are found, spiders are almost certainly not far away. However, the competition between the two groups is not all one-sided. Most insects have wings, which give them an escape advantage over all but the swiftest jumping spiders, but carry them straight into the sticky traps of web-building spiders. Moths, on the other hand, have a protective covering of loose scales, and this enables them to bounce off most webs.
Wasps, those consummate predators of the insect world, have a gruesome range of spider-killing techniques. The mason wasp, which decorates Northland with its adobe nurseries, deposits several living but paralysed spiders in each egg compartment, guaranteeing the hatchling wasps a fresh meal.
Other parasitic wasps have the ability to sneak up on a spider and deposit a single egg on its abdomen. The resulting larva eats the host alive.
Some scientists see in the relationship between spiders and insects an evolutionary tug-of-war in which each group tries to gain the advantage through the development of evermore-clever attack and defence strategies. In all likelihood, though, spiders are their own worst enemy. While the few communal species, like the Avondale spiders, can differentiate between their own kind and “foreigners”, most spiders shoot first and ask questions later, taking anything that comes their way—and that may be another spider.
A few species have specialised in taking only spider prey, and have developed complex behaviour patterns such as fooling another spider into thinking the predator is prey.
The white-tailed spider Lampona cylindrata frequently tackles the grey house spider Badumna lonquuipes, sometimes taking up to an hour to work its way stealthily into position in the host web. Pretending to be a struggling insect, it lures the host out from its retreat, then pounces, usually getting its fangs in before the house spider realises its mistake.
In one respect, spiders have definitely outclassed their insect opponents. It is the ability to make and use silk. This fact was brought home to me on a cool early autumn morning, not far from the settlement of Beachlands, east of Auckland. The sun was just rising above a ring of hills, and wisps of mist still clung to the paddocks. Hundreds of orbwebs, heavy with dew, glistened between the wire and battens of a typical farm fence.
But beyond the fence, something was not quite right with the grass. Apart from a few cattle tracks, the field looked completely white, as though covered with hoar frost or snow. Yet only in this one paddock.
Closer inspection solved the mystery: millions of spiders had spun an enormous silk “spiderdown” across the field—a veritable gossamer city. According to the farm manager, this is the hay paddock, and the webs appear for a fortnight in the same place, at about the same time, each year.
“One year,” he said, “the tractor broke down in this paddock, and when we went back next morning to start it up there were thousands of spiders crawling all over it.”
The silk shroud is the work of literally millions of tiny money spiders—which normally live in this field feeding on springtails—each spinning a tiny sheetweb between the tips of the tallest grass blades, so that the covering becomes almost continuous.
As I watch, fine strands of silk, barely visible, drift through the shafts of morning light, and occasionally I can see a tiny spider attached to the end of one. These spiders are “ballooning” on the wind in an effort to disperse themselves far and wide, and I am told that just days previously the air had been thick with them. As the sun begins to dry the upper railings of a wooden fence, other spiders begin to run back and forth trailing silken lines, occasionally pausing to stand on tip-toes with abdomen pointed skywards in an effort to get airborne. Every once in a while, one manages to disappear on a gentle breath of wind.
Though most of the spiders here are mature, it is in this way that the young of many web-building species begin an independent life. Finally free of the egg sac that protected them as eggs and as helpless hatched spiderlings, they, too, hang out a thread to see where the wind will take them. They often float to high altitudes, even into the jet stream, and ballooning spiders have been collected by aircraft from heights of 6000 metres and more. That they have also landed on the decks of ships more than 300 kilometres from land shows how far they can travel by this method.
The ability to travel by air and to go for long periods of time without food (in some cases, a year or more) has enabled spiders to colonise nearly every corner of the globe—and is the reason why Australian spiders frequently turn up in New Zealand, blown across the Tasman by the prevailing westerly winds. However, it is their ability to make prey-catching webs that has become the spiders’ trademark, and the orbweb is the pinnacle of that art. Constructed with marvellous geometric precision, these webs, which look like bicycle wheels, can be up to two metres across, and some are made of such strong silk that people inadvertently walking into them recoil with the impact.
In New Guinea, orbwebs are collected for use as fishing nets, either by leaving a bamboo loop in a strategic place for the spider to build a web in it, or by dragging a loop through a number of existing webs. The resulting net is quite strong enough to support the weight of a fish flicked out of the sea.
The most impressive orbwebs seen in New Zealand are the work of the golden orbweb spider, Nephila edulis, which balloons across the Tasman most years and sets up its web in late summer. This visitor has not yet become a permanent resident, although another Australian orbweb spider, Eriophora pustulosa, has, and is now common throughout the country.
By day. this spider hides in a suitable retreat. It emerges in late afternoon or evening to make repairs to its web (being large, the webs are often damaged by birds), then spends the night either head-down at the hub of the web, with its legs resting on the radial threads, or back in its retreat, holding a “signal line” which is attached to the hub.
Like all web-builders, the orbweb spider is almost blind, and relies on an acute sense of touch to work out what is happening on the web. This it does with amazing accuracy, by learning the vibration “fingerprint” of each and every intruder. As one spider researcher put it, these spiders “live in a world of melodies played on silk”. A fly blundering into an orbweb sets up a “tune” which is relayed along the radials to the centre. The spider knows immediately where the insect is. and runs unerringly towards it.
After capturing and injecting their prey with venom, orbweb spiders wrap them in silk and often leave them suspended from the web, to be consumed at their leisure. Small prey are rotated by the spider while a sheet of silk is released from its abdomen—the technique is something like winding cotton on to a cotton reel. Larger prey cannot be so easily manipulated, and the spider walks around them, coating them with silk as it goes. The end result is the same: a ready-to-eat prepackaged meal!
The question is often asked, Why don’t spiders get caught in their own webs? There are three reasons:
- the owner of the web knows which silk lines are sticky and which are dry, and therefore knows where to walk.
- web-building spiders have modified feet which can grip a silk thread without it coming into contact with their legs.
- the legs are covered with an oily substance secreted from a gland in the mouth during preening, so even if contact was made with a glue thread, the leg would not stick.
Orbs are usually webs of the wide open spaces, and are hung vertically to present the maximum surface area of web to insects flying by. Another web-builder, the large sheetweb spider Cambridgia foliata, makes a horizontal trap, up to a metre wide, which can often be seen in the bush and also around North Island houses. This long-legged spider, if not hiding in a retreat in an adjacent tree, will patrol the underside of its web, seeking prey knocked down by a maze of non-sticky threads which extend upwards from the sticky platform. One of these spiders reportedly attacked and killed a wax-eye which had flown into its web, though it did not attempt to eat it.
A spider’s web effectively amplifies its senses, providing it with information that would normally be outside the range of its own sense organs. But a large web is also expensive in terms of protein used and energy required to build and maintain it. Some spiders build more economical webs, while others dispense with them altogether, relying on camouflage, ambush or stealth to trap their prey.
The webs commonly encountered on the outside of buildings are those made by the grey house spider, which is abundant throughout the country. For those of us who are not particularly house-proud, these spiders are too abundant, building their ladder-patterned webs around windows, under eaves and even under the bottom edge of weatherboards. The webs usually have a funnel leading to a concealed hiding place, like the gap between a window and its frame, from which the spider suddenly emerges to subdue any prey that has become ensnared in the web.
Also common around houses are the smaller and more uniform webs of the cobweb spider, Achaearanea verucu lata. This spider belongs to the same family as the katipo and red-back: the theridiids. Members of this group usually immobilise their victims by backing up to them and, using a row of bristles on the end of the hind pair of legs, spraying liquid silk across the prey. Struggling is self-defeating because it produces the tension required to make the silk harden. The victim is then bitten and paralysed.
A web-building Australian spider which is becoming more familiar in our gardens is the gaudily coloured two-spined spider. This yellow-green-and-white beauty is often found sitting under a citrus leaf during the clay. With its legs tucked neatly under its body, it looks more like a blob of guano than a spider, and for this reason is referred to as one of the “bird dropping” spiders. As well as being able to make a soft orbweb at night (which is taken down and eaten before morning), the spider can also produce a scent which mimics the pheromones released by female moths to attract males.
The use of sex scents to lure moths to their doom is practised by other bird dropping spiders, which simply hang by a strand of silk, exuding scent and grabbing male moths that fly too close.
Tunnelweb and trapdoor spiders, common in nooks and crannies in bush settings, build simple traps in the ground, either using existing holes or excavating new ones with their jaws, palps and first pair of legs. They line their burrows with a smooth, soft silk.
Some trapdoor spiders make a wafer-like lid by first enclosing the entrance completely with silk, then biting through two-thirds of the margin to leave a hinge. They decorate the lid to hide it. Silk lines lead away from the mouth of their burrows and act as trip wires, warning the spider of a potential meal. The spider usually pounces from near the mouth of its retreat, where it can be found waiting patiently at night, and drags its victim into its lair.
One of New Zealand’s commonest indoor spiders—responsible for the scruffy webs which appear on ceilings and in the corners of rooms—is the daddy-long-legs, Pholcus phalangioides. It occurs throughout the North Island and in warmer parts of the South Island.
This fragile-looking spider is no laggard when it comes to trapping prey, though it is always wary about biting off more than it can chew. If something altogether too large is detected in the web—a human finger, for instance—the spider reacts with a frantic whirling motion, possibly in the hope that the intruder will be shaken free, or, if it is a predator, that it will become confused.
If the spider detects prey in its web, it moves quickly from its upside-down resting place, and, keeping the victim at bay with its second and third pairs of legs, rapidly trusses it up by winding silk around it with its hind legs. The daddy-long-legs does possess poison glands, but it makes such a good job of tying up its victim that it hardly needs to use them.
While web-building may seem to represent the height of spider achievement, most arachnologists consider hunting spiders, which catch prey “on the hoof” instead of using webs, to be the most advanced. Some hunters are especially sensitive to the vibrations of potential prey, thought to be detected through special hairs on their legs, and the eyesight of jumping spiders is so good that they can focus precisely on prey to estimate its distance before pouncing for the kill.
Hunting spiders include wolf, nurseryweb, crab and lynx spiders. All quickly seize prey which comes within range with the front pair of legs, and inject venom. Once the toxins take effect and the prey ceases to struggle, some of these spiders may move on, eating the victim still transfixed to their fangs.
Wolf spiders are proficient ground predators, and have little use for silk in their day-to-day lives. They scurry through the undergrowth in short spurts. pausing frequently to watch for movement or sense vibrations that might betray unsuspecting prey animals nearby. Once detected, victims are pounced on with lightning speed, then dragged away to be devoured.
At egg-laying time, though, silk becomes important, and the female takes great care to produce a strong egg-sac which she carries around beneath her abdomen until the spiderlings hatch. First, she lays out a square of silk on the ground (much like a holidaymaker laying out a tablecloth for a picnic). She deposits her eggs in the middle of it, then carefully gathers up the corners and wraps the precious contents into a bundle. More silk is bound around the bundle to make a spherical silk ball, which she then attaches to her spinnerets.
As the young “wolf cubs” hatch, they climb on top of their mother’s abdomen and are piggy-backed around until they are ready to fend for themselves.
The nurseryweb spider, Dolomedes minor, whose semi‑opaque silk nurseries litter the landscape during summer, also carries its egg-sac around, but at the front, held by its fangs and palps. Surprisingly, it still manages to hunt while thus encumbered.
The nursery is purpose-built for the protection of the newly hatched spiderlings. When the spider senses her young are not far from their first moult (they are still inside the egg-sac at this stage) she climbs to the top of a bush (commonly gorse or broom) and spins a shelter which is both weather-and predator-proof. She places the egg-sac inside, seals up the nursery and then, at night, straddles it. During daylight she seeks shelter, keeping out of sight of predators.
The nurseryweb’s relative, the grey water-spider, hunts around shingle riverbeds and lake shores at night. By placing its front legs on the surface of the water, it can detect the wave ripples of struggling insects that may have fallen in. The spider simply scoops the prey from the surface, often running across the water to seize its meal.
This versatile spider is able to live under water too, taking a supply of bubbles with it and spending as long as half an hour submerged. As well as preying on crustaceans and aquatic insects, it has been known to catch small fish.
Many crab spiders rely on cryptic coloration to ambush unsuspecting insects which come within reach of their elongated front legs. They derive their name from the fact that they scuttle sideways and hold their front legs wide like a brandishing crab.
Lynx spiders—characterised by a pointed abdomen and long, spined legs—hunt around low shrubs, preying on small flying insects which land within reach. Like jumping spiders, the lynx relies on good eyesight combined with impressive agility to catch its prey.
Jumping spiders, especially the endearing, big-eyed house hoppers, are often seen indoors, hauling around prey that is much bigger than they are. Like a cat, the jumping spider will first fix potential prey with a stare, then either stalk or run towards it before pouncing.
It is thought that the small eyes on top of their heads act like wide-angle lenses, picking up general movement, while the two huge forward-pointing eyes allow clear target identification and give binocular assessment of distance before the spider springs.
The prize for innovative hunting must surely go to the spitting spiders of the genus Scytodes—foreigners which occasionally turn up in New Zealand. These spiders immobilise their victims by showering them with glue. The spider squirts two streams of gum from glands at the front of the head, simultaneously vibrating its jaws from side to side so that the fluid falls in a zigzag pattern. The prey is glued to the ground where it stands.
Another clever hunter from the tropics looks like an ant, and even walks like one, using six legs for locomotion and holding the front pair over its head like an insect’s antennae. This mimic is so good that it can even get inside an ant nest unsuspected, but it only takes an ant to rub antennae with the deceiver and the ruse is up . . . but dead ants don’t tell tales!
It’s dinner time at our house. A praying mantis has blundered into a grey house spider’s web which covers the corner of the living room window, and the beautiful, green insect hasn’t got a prayer. With the first struggles, a pair of long, dark legs appear on the window frame from the spider’s retreat in the gap above it. Then the whole spider can be seen, sharply contrasting with the pale paintwork behind her as she sits and feels out the situation, then moves towards her prey through the webbing tunnel that leads from her hiding place.
She pauses again, as if to plan her strategy of attack. Then, in a few swift movements, she nimbly closes the gap between them, grabs the nearest mantid leg with her jaws and palps and pulls the victim back up towards the corner, further entangling it in the fine cribellate webbing—a kind of super-fine barbed wire that she’s made from silk produced in a special gland called the cribellum and combed out by structures on her fourth pair of legs, called calamistra. One of her excited youngsters runs around and over the combatants in this one-sided struggle.
Knowing she is safe from the insect’s jaws, the grey house spider proceeds to inject subduing venom—first through the foot of the insect, then part way up the leg, into the wing and finally the body—over a period of an hour until the mantis is still.
Nearly all spiders use venom to subdue their victims—in fact, only one small family, the Uloboridae, lack poison glands, and rely completely on their jaws to despatch prey. When a spider is about to bite, its fangs, which are otherwise folded away into grooves in the basal segments of the chelicera (jaws), are opened out like the blades of a pocket knife to extend downwards. The spider presses the basal segments against the prey as the fangs penetrate its exoskeleton. Strong internal muscles inject the venom into the victim’s body.
Whichever way they obtain their prey, the method of eating is similar throughout the spider world, and can turn a shrivelled spider abdomen into a turgid balloon overnight. Unlike, say, a praying mantis, which chews up its prey and swallows the pieces, spiders cannot take in food particles which are larger than a thousandth of a millimetre, and must liquify the contents of their prey before ingesting the nutrient-filled “soup”.
In the same way that spiders use a web as an extension of their sensory organs, they use the prey’s own body as an extension of their gut—it becomes both food processor and serving dish! The spider injects digestive enzymes into the body of the prey and, using strong throat muscles and the spider’s unique “sucking stomach”, takes in the partially digested fluid into its midgut to complete the digestion process.
By “kneading” prey with their jaws, many spiders crush and rupture the exoskeleton of their victim as they eat. This brings the prey’s tissues closer to the spider’s mouthparts so that they can be thoroughly bathed in digestive juices.
By this means, my grey house spider was able to feed on all parts of the narrow, tubular mantis body, and by morning all that remained was a scene of carnage—disembodied wings and legs, and a few more guano-like droppings on the window sill below. However, there is not always such destruction left after a spider’s meal. Eaten prey can sometimes look as if it has not been touched—the exoskeleton left intact even though the insides have been sucked out.
Crab spiders feed in this way, usually starting at the head. Because the prey remains intact, the spider’s sucking generates a vacuum within the prey’s body, and the spider cycles the fluid it extracts between its own digestive system and the body of the prey. (It’s a bit like what happens inside a small fruit juice carton when you take a strong suck through the straw, then relax.)
This method of feeding enables the spider to mix digestive fluid with parts of the prey that are not in the immediate vicinity of its mouthparts. The spider refluxes the semidigested mess back and forth, adding digestive fluid and finally swallowing the whole lot when it is liquid enough. Once the spider has dissolved as much of the prey as it can from the head, it will switch to the other end and start again.
Christchurch spider researcher Simon Pollard has studied this process under a microscope, and says that it rivals the more disgusting elements of any horror film!
While a crab spider’s meal is neatly packaged within the prey’s own exoskeleton, orbweb spiders package their prey in silk. Within the silken bag, prey is crushed and dissolved, the spider using its palps to rotate the food parcel so it can inject digestive fluid and suck up nutrients. Once the meal is over the remains, in their silken shroud, are cut free and dropped from the web.
Most of the spiders commonly seen around our liouses and gardens are immigrants . . . and Australian ones at that. Last century, most of the foreign spiders finding a home here were from Europe, particularly Britain, reflecting the nationality of the colonial travellers of the time. Spiders like to travel with people or their possessions. If they’re not hitching a ride in a backpack they’re hiding away inside something else we’re carrying.
Recently, the Ministry of Agriculture and Fisheries in Auckland was notified that a white-tailed spider, which during the day likes to hide away in a small crack or crevice, had found its way here inside the workings of a transistor radio. Though not a particularly alarming event (this species has been resident here for over a century and is widely established), it does illustrate how difficult interception of these beasties can be at our points of arrival. The practice of spraying the cabins of arriving aircraft with “residual” insecticide, which has largely replaced the spraying of quick “knockdown” insecticide, is not going to stop stowaways such as this.
It is likely that the Holden car and the ubiquitous shipping container have been vehicles for the unwitting introduction here of a much less welcome spider: the notorious red-back–one of the “widow” spiders of the genus Latrodectus. Red-backs have particularly toxic venom and a nasty reputation, which includes biting people while they’re using the out-house. The species is now firmly established in New Zealand in places as far flung as Northland, New Plymouth and Wanaka.
Unlike its local cousins—the two species of katipo, which prefer relatively out-of-the-way habitats and are found only near the sea—the red-back has an unfortunate liking for the places we inhabit. Also unlike katipo spiders, red-backs have the ability to establish a population of just one fertilized female—sibling males and females (and there can be a hundred or more from just one egg-sac) can breed together.
Does this represent a potential national disaster? Probably not, says Dunedin arachnologist Lyn Forster, who has studied the red-back for many years, though she warns that the intruder should not be taken lightly: “Although Australians have learned to live with the red-back, they are more likely to have been aware of its potential danger since childhood. Nor should it be thought that few Australians get bitten. A survey of cases between 1968 and 1976 showed that almost 2000 people had been bitten, and this was believed to represent only 50 per cent of the actual figure.”
Up to 1956, when an antivenene was introduced, there were at least 13 deaths from red-back bites in Australia. The ready availability of antivenene has prevented fatalities since that time, but hospitalisation from bites is still common.
By contrast, there have been no confirmed fatalities from katipo bites, though by naming it “night stinger”the Maori were evidently well aware of its habit of biting those unfortunate enough to encounter one while bedded down on sandy beachfronts.
While a female katipo has an abdomen about the size of a garden pea. the red-back can be nearly twice this size. Both have a red hour-glass marking on the underside of their abdomens—the mark of the widows, which distinguishes them from other similarly-shaped spiders such as Steatoda capensis, the “false katipo”.
Auckland MAF entomologist Ruud Kleinpaste is particularly aware of the problem of red-backs arriving in containers and cars, as well as black widows arriving in shipments of Californian grapes. Until April of this year he was keeping alive the spiders he intercepted, and using them to help in the training of quarantine staff.
Kleinpaste, a long-time campaigner for spider rights, is not particularly alarmed that the red-back has become established here, and seriously doubts suggestions that a large, extremely venomous and aggressive hybrid would result from interbreeding between red-backs and katipo.
He offers to show just how non-aggressive Latrodectus spiders are by allowing a large black widow to walk across his hand—though he’s not entirely happy about it, as one of his red-backs had given him a painful bite a few days earlier (the result of mishandling, he assures me). It turned out to be my only opportunity to see a live black widow. A few weeks later Kleinpaste was ordered to destroy his collection when someone who had attended the public spider display in Palmerston North queried the legality of having black widows alive and biting in New Zealand.
Just how bad can a spider bite be? That depends on the type and condition of the spider, the amount of venom it injects into you, and how you react to it. There is no doubt that the venom of a Latrodectus spider can deliver a fatal dose—though the availability of antivenenes has made fatalities very rare. On the other hand, Ruud Kleinpaste’s red-back bite was no worse than, perhaps, a bee sting, with localised pain for a few hours afterwards, but no noticeable effects the next day. By his own choice, he went without antivenene.
Even so, the consensus among spider experts is that, if bitten, you should go directly to your GP or nearest hospital accident and emergency department. If at all possible, take the spider (preferably in a recognisable condition). This is because some patients can have an adverse reaction to Latrodectus antivenene, and doctors prefer to administer it only if they can be fairly certain that the bite is from a Latrodectus spider.
As well as spoiling New Zealand’s “all things bright and beautiful” image, foreign spider introductions have been upsetting the balance of local species, and one of the more serious examples involves none other than the katipo.
Right now, this spider is being displaced by a South African immigrant, Steatoda capensis. A recent study has shown that the katipo is losing out not because it is an inferior predator (in face-to-face combat, the katipo usually kills its opponent) but because it is slower off the mark in recolonising an area after a storm or other disturbance.
In such instances, Steatoda are able to move in quickly from nearby habitats and take over the best sites. They also out-breed the katipo during summer months, and continue to do so during winter, when the production of katipo egg-sacs is rare. Homeless katipo young end up being chased away or eaten by mature Steatoda which have already established their webs.
Loss of the katipo’s preferred habitat—under driftwood and among the marram grass or lupins on the sandy strip behind many beaches—through the construction of parking lots, barbecue areas and so on, is also having a deleterious effect. The net result is that there are now far fewer katipo than there used to be 20 years ago.
For a male spider, the thought of positioning oneself directly beneath the needle-sharp fangs of a hungry female which, for its entire life, has done nothing but eat any arthropod which gets close enough, must be off-putting, to say the least. Yet this is what males are called to do during mating, and many have devised elaborate courtship rituals to ensure their survival. In fact, the idea that male spiders are routinely eaten after mating is a myth.
In all spiders, males transfer sperm to the female not with a specific sex organ, but with their palps. These vary widely between species—from simple “eye-droppers” to complex lock-and-key devices which ensure total fidelity within the species.
Regardless of their complexity, a spider’s palps cannot reach the groove on the underside of his abdomen that leads to his internal testes, so he must spin a small web on which to deposit seminal fluid, then dip his palps in to charge them with sperm. He then goes looking for a female
When he finds one, he signals his intentions by going through a courtship display. Some of the web spiders try to gain the affections of a mate by sending the right vibrations through the threads of her web. Males of other species tap out a “letter of introduction” with their feet, produce scents, perform dances, or use a combination of these routines.
One of the favourite stories told by arachnophiles is of the courtship of the green flower spider Diaea. The male’s courting behaviour involves using silk strands to loosely tie his mate onto a leaf—a sort-of spider bondage session, though the threads are not thought to be strong enough to actually hold her against her will. In fact, it seems the main effect of male courtship is to cause the female to fall into a trance. While she is mesmerised, he can mate in relative safety.
Some males take no chances about their post-nuptial survival. In some species the male waits until the female moults, then makes his move when her fangs are too soft to do any damage. Jumping spider males literally leap for their lives after mating, hoping to clear the female’s hungry embrace in a single bound.
During mating, the male must insert his palps into an opening on the underside of the female’s abdomen. At its simplest, this means poking the tip under a flap covering a single opening. Spiders with complex palps have a more involved procedure, applying the left palp to the left opening and the right to the right opening, perhaps several times.
Female spiders can store sperm for varying lengths of time, sometimes months, before using it to fertilise their eggs. This means that if the female mates with more than one male, the sperm of subsequent males will be “in competition” with each other for her eggs. In some species, this fight for fertilisation has led to what some describe as an evolutionary “arms race”, where males have developed more and more sophisticated methods to protect their own genetic investment from rival males. For example, some male spiders plug up the female after mating to hinder rival males. Others have hooks to scrape out the plugs, removing the previous male’s sperm and replacing it with their own.
It all sounds very clever, but just how smart are spiders? Robert Jackson, who heads a group of spider researchers at the University of Canterbury, says his team is finding evidente that these small animals are surprisingly intelligent.
Mary Whitehouse, one of Jackson’s students, has a particular interest in the web pirate Argyrodes antipodiana, known as the dew-drop spider. This tiny spider with its shiny silver abdomen is found in its dozens on the webs of much larger spiders, like orbwebs, where it steals food from the host. By moving very slowly, it is able to sneak up unnoticed while the host is engaged in wrapping its prey or feeding. Cleverly, Argyrodes feeds from the opposite side of the web to the one the host is on, and, for added safety, builds its own support web nearby, to which it can escape if the host makes a lunge for it.
As well as pilfering from the master’s larder, these mini-bandits are not averse to biting the hand that feeds them—literally. When the orbweb spider is moulting, and therefore vulnerable, Argyrodes may attack and kill it, even though the orbweb is perhaps 50 times its own size. Argyrodes also captures orbweb spiderlings by mimicking their behaviour.
Argyrodes is not a full-time thief. It sometimes works for a living by spinning its own small sticky web next to the giant orb, and catching its own flies. Even in this activity, however, it can’t keep its jaws to itself, and often eats the host web, recycling the silk for its own creation.
Not only are spiders smart, but they’re useful too. Ruud Kleinpaste finds it extremely ironic that people use an insecticide to kill “God’s greatest aerosol can”. Kleinpaste says spiders are essential pest control creatures in forests, grasslands—any well-established habitat or ecosystem.
Worldwide, spiders kill more insect pests than all birds do, and far more than commercial insecticides. There have been many estimates of what this amounts to—one guess is that spiders eat the weight of the entire human population every year! Without spiders, the world would be crawling with insect pests.
There is much to praise in spiders, but still the negative image persists: they are the king of the creepycrawlies. However, the humble house hopper, a jumping spider often found in our homes, has been doing its bit to promote the spider cause. These spiders are endearing little creatures—their large eyes give them the appearance of a cuddly Walt Disney character.
Even Margaret the spider phobic isn’t afraid of them. Somehow, she sees this creature as being something other than, well, a spider!