In the darkness, a stalker lurks. Millimetres away, a cockroach preens itself, unaware of the danger. The predator’s antennae extend towards the insect, curling on contact. Sensory bristles brush the cockroach’s body with feather-light touch.
The antennae withdraw. Silently, the head rears up, revealing a mouth with lobe-shaped lips and curved mandibles, flanked by a pair of tuberous nozzles.
Suddenly, from each nozzle shoots a jet of translucent fluid that hits the unsuspecting cockroach like twin blasts from a glue gun. The insect’s struggles simply ensnare it more securely in the sticky threads. Soon, its attempts to extricate itself grow increasingly feeble, and it lies still, enmeshed.
A strand of glue hangs between victor and vanquished. Unhurriedly, the head draws back to break it.
Now 15 pairs of stumpy legs bear the hunter to its prey. The mouth opens wide—so wide the animal’s front end gapes and begins to turn back on itself—then clamps onto the underside of the cockroach, at which it gnaws repeatedly. As the mandibles tear through the cuticle, saliva rich with digestive enzymes pumps into the punctured body cavity. Within minutes the hapless cockroach is dead, its inner tissues turned to soup.
Over the leisurely hours that follow, the killer sucks up every drop of liquefied flesh. The cockroach’s exterior armour plating collapses.
Satiated, the grisly gourmand turns from the scraps, crawls to a nearby log, and slips into the cool and damp beneath. Tonight’s feast will see it through another week, perhaps two.
Such scenes of capture and consumption are a daily occurrence throughout New Zealand, yet the predator concerned is not widely known, its recent appearance in a series of “creepy crawly” postage stamps notwithstanding. It is most commonly called peripatus—from the same Greek root as peripatetic, meaning itinerant or wandering, a term particularly associated with Aristotle’s habit of discoursing with his philosophy students while strolling about the Lyceum in ancient Athens. The animal is also called the velvet worm or walking worm—references to two of its more obvious traits.
Peripatus are found largely in the southern hemisphere—in Australasia, south-east Asia, Africa and Central and South America. First described by Reverend Lansdown Guilding, who discovered them on the Caribbean island of Saint Vincent in 1826, they have defied easy classification. Guilding called his find an “aberrant mollusc,” but others subsequently observed characteristics in common with both arthropods—the large group of hard-bodied invertebrates that includes insects, centipedes, millipedes, crustaceans, spiders and scorpions—and soft-bodied annelids, or segmented worms.
All arthropods share a number of distinguishing characteristics, notably the fusion of adjacent body segments into functional regions (such as the head, thorax and abdomen of an insect), a tough exoskeleton and jointed limbs. Worms, on the other hand, have many identical body segments, a soft outer skin or cuticle, and no limbs. Peripatus swings both ways. It has a distinct head made up of three segments (insects have six) but otherwise a body that is wormlike. Its skin, although thin and flexible like a worm’s, is more similar in composition to the skeleton of an arthropod. And it is equipped with limbs, although these are unjointed and conical in shape. If anything, peripatus most resembles a caterpillar, except it never becomes a butterfly.
Judged according to these criteria, peripatus qualifies as a primitive arthropod or a supersophisticated worm, occupying an evolutionary position between the two groups. Some authorities favour its arthropod qualities and classify it as a relation of the millipedes and centipedes, but it is more commonly placed in its own phylum—Onychophora (Greek for “claw-bearer”), an offshoot from the main line of annelid and arthropod evolution.
On the trail of this taxonomic oddity I have come to Waikaia Bush, a 10,500 ha island of beech forest nestled in the farmland and mountains north of Gore. Eric Edwards of the Department of Conservation and his colleagues are surveying this forest remnant for a number of invertebrates, including two varieties of peripatus. I have joined them at a crib at Piano Flat—an open, grassy area on the east bank of the Waikaia River—for a nighttime search for velvet worms.
Peripatus lead a nocturnal existence to minimise the danger of drying out, for, like earthworms, they are unable to control water loss through their skin. As a further safeguard against dehydration, they make their home where it is cool, dark and humid. Typically they are forest-dwellers, living beneath or inside rotting logs, under rocks and in leaf litter, but they also turn up elsewhere. In some parts of the country they frequent suburban gardens, while in places where forest cover has disappeared, soil crevices, rocks and remnant logs may continue to provide sanctuary.
Peripatus have also been found in caves and in alpine conditions. Indeed, cold seems to be no impediment to the hardier varieties. They have been discovered under rocks on the side of Tasman Glacier, where temperatures commonly fall below freezing.
Come nightfall we set out along a bush track. Earlier in the day the beech forest appeared lifeless, with not so much as a fantail in sight. Now it has been transformed. Caught in the light of our probing torch beams, a multitude of little creatures scuttle, creep, burrow, spring or fly.
Spiders—nimble hunters and trap-spinning sheetwebs—frequent the vertical world of the tree trunks. Two craneflies, locked in mating embrace, hang from a low branch. Gleaming moss beetles shine like tiny supernovae from around the base of a silver beech. In one small coprosma bush, in the company of four goggle-eyed whistling frogs, we see two kinds of weta, a glistening vein slug and the empty case of a darning-needle dragonfly. In practically every bunch of prickly shield fern we encounter half a dozen copper-coloured fern weevils, each the size of a dollar coin, browsing the fronds.
Jet-black carabid beetles, millipedes, slaters, dangling bag moths (actually caterpillars), orange-spined springtails, native cockroaches, click beetles, tiny ornate snails, a miscellany of maggoty larvae, a bright-green crab spider crawling along its gossamer tightrope—all are out and going about their business as we amble through the dark, training our lights over mossy banks and up trunks, pulling back flaps of bark, lifting logs, peering into crevices. But of that arch predator of the night, the stealthy peripatus, there is no sign.
We shall have to try again in the morning, when, like Dracula, our quarry has retreated to the security of his basement hideaway.
Peripatus tend to be distributed only thinly through the litter system, with large aggregations a rarity. A day’s back-breaking, finger-shredding labour—lifting and breaking open logs and hefting boulders to one side—may be rewarded with the discovery of only a couple of inert creatures. Fortunately, in daylight we have little difficulty running the velvet killer to ground.
No more than five minutes’ walk along the riverbank, rolling back only my second log of the day, I spy among the crumbling detritus what might easily pass for just another fragment of litter. But something about the texture and colour prompts me to lean closer. Gently, I pick it up and bring it close to my face.
It looks rather like a dry slug with legs, about a centimetre and a half long. Hunched in sleep a moment before, it has begun to straighten, pale underside uppermost. Frond-like antennae curling, 15 pairs of stumpy legs treading air, it raises its head and turns its upper body to one side. Its front limbs touch down on my palm, and, pair by pair, the remaining legs follow. On all pegs at last, it sets off in ponderous fashion across my hand.
Species vary in the number of legs they possess—from 13 to 16 pairs in New Zealand and up to 43 elsewhere. Males are smaller than females and may have fewer legs, although in New Zealand variable leg number has been observed so rarely that it has not been related to sex and is quite probably the result of individual genetic variation.
At the end of each leg is a tiny foot, bearing a minuscule pair of claws, but the appendages after which this group of forest denizens has been named are not put to use unless the going is slippery or vertical. Over easy terrain, the feet are raised and spiny pads on the underside of each leg bear the animal’s weight.
A peripatus may be stumpy-legged, but it has an elegant, even sensuous, gait. Each leg moves slightly out of phase with the next one along and, at higher speeds, with its opposite number. It stretches as it swings forward, then the spiny pads on its underside are placed on the ground, followed by the claws if needed. The leg then contracts, drawing the body forward. As the animal accelerates, it increases its stride and fewer feet touch the ground at the same time. As well as being able to change gear, peripatus can walk backwards, a great help when manoeuvring in and out of crevices.
With my free hand I fish out a lens to take a closer look. The outer skin is covered with countless tiny nodules, like so many globe artichokes or pine cones, arranged in bands that encircle the trunk, legs and antennae. The larger of these papillae narrow to a sensory bristle, and all are covered with minute scales, imparting to the skin its characteristic dry, soft texture.
This peripatus is predominantly a light golden brown in colour, with a darker stripe down the middle of its back, but other varieties come in more striking livery. Bright red, orange, yellow, green and blue form intricate patterns of stripes and diamonds against a dark background of purple, blue-black or brown, reminiscent of a Turkish carpet. There are a few largely single-colour species—the Nelson region is home to a pure indigo-blue variety, for example. A rare apple-green animal, with purple legs and a distinctively smooth skin, has been reported in the Ben Ohau Range above Twizel and in the Remarkables, while an equally rare creamy white one, also with smooth papillae, has been seen in the Lewis Pass. Occasional albinos have also been found.
Every two to three weeks a peripatus sloughs its outer skin. Waves of muscular contraction travel the length of the animal’s body, tearing the cuticle open down its back. One pair at a time, the legs step free, and, as the shed skin gathers towards the rear end like a crumpled garment, the peripatus bends around to speed up its final removal with its jaws, then eats it.
Such recycling is a must—protein is far too valuable a resource to discard on the forest floor for passing scavengers. Peripatus also consume their own glue-spit, and have been observed to gobble this up as an entrée while waiting for the digestive enzymes they have injected into their victim to take their full, dissolving effect.
Getting into its stride, my captive has stretched itself out to almost 3 cm. This is a pretty average length among New Zealand peripatus, which tend to be of modest dimensions. Our largest rarely exceed 5 or 6 cm—giants next to the 5 mm tiddlers in some parts of the world, but dwarfed by the 15 cm whoppers that tread tropical forest floors.
At the base of each antenna is a dark, beady eye. There is evidence to suggest peripatus eyes are capable of registering an image, but it is unclear how helpful this might be in the close, dark world these animals inhabit. Their eyes probably just detect light, thus warning of the danger of drying out. Two species—one in Tasmania, the other in South Africa—get by without eyes or skin pigment. Blind and pure white, they appear to have evolved in a cave or subterranean environment.
I have to roll my peripatus onto its back again to view the circular, lobe-lipped mouth with double pair of sickleshaped mandibles, and the two lumpy “gun turrets”—oral papillae—used to such effect in the capture and consumption of prey. Both the jaws and oral papillae, as well as the antennae, are pairs of modified limbs.
Peripatus are opportunistic and will scavenge in preference to expending energy on hunting. When they do hunt, their characteristic sluggishness answers the need for stealth. They stalk at close quarters, probably gauging potential prey by smell and by sensing vibrations through the ground. Sometimes they approach close enough to use their tactile antennae, the tips of which are covered with receptors.
All manner of fellow invertebrates feature on the peripatus menu: isopods, termites, spiders, baby crickets, cockroaches, weta. Some prey may be as large as, and more nimble than, their hunter. Yet a peripatus must exercise care. Energy—and glue—cannot be wasted on a creature offering only minimal nutritional return, or one likely to escape or, worse still, fight back and make its own meal out of its assailant.
The dramatic manner in which a peripatus incapacitates its victims serves also as its means of defence, and it will swing its head round and fire across its own body if attacked from behind or the side. Instantaneous on the draw, and accurate up to 7 or 8 cm (some overseas species can drill a standing cricket at two or three times that distance), this is not a customer to be trifled with. Its range may be even greater—as much as 50 cm in some parts of the world—but accuracy tends to diminish with increasing distance. The slime itself,ejected in liquid form and denatured by the air so it becomes sticky, loses its adhesive quality after a few minutes.
Peripatus is itself undoubtedly a tasty morsel for other, bigger forest-dwellers, although exactly which ones is not known. Kiwi, with their long probing beaks, are likely consumers; also saddlebacks, robins, weka and, in their day, huia. Giant centipedes, some of the larger spiders and ground beetles and nocturnal mammals such as hedgehogs probably also partake.
The animal in my hand has taken about a minute to trek diagonally across my palm. (Peripatus in warmer regions are fleeter of foot—some overseas species can pound along at 60 cm a minute.) A gob of translucent goo bubbles from beside its mouth. There is no force behind this act—the liquid spills rather than splats—but it is presumably a protest at being roused. I return the peripatus to its snuggery and roll the log back into place.
A peripatus can squeeze, Houdini-like, through apertures as tight as one-ninth its girth. Its vital organs—heart, gut, nerve cord, salivary glands, slime glands and reproductive organs—can move within the body cavity to accommodate such constriction. There are no lungs from which the air might be squeezed. As with insects, tiny openings in the skin allow oxygen to pass through fine tubes, or tracheae, directly to the internal tissues. But, unlike insects, peripatus have no mechanism for regulating these openings, and vital bodily fluid is easily lost through them.
That night we go looking again, hoping to see peripatus on the move. We leave the track and pick our way into the bush. Here a trickling stream is flanked on either side by a stony clay bank overhung by roots. Galaxies of glowworms radiate in the dark. Eric Edwards plays his torch over this miniature grotto.
“I’ve seen heaps of peripatus here on the bare earth,” he says. “Warm summer nights seem to bring them out. They like the humidity.”
Tonight we are less fortunate. It is drizzling, and the air is cool. Apart from the glow-worms, signs of life are few, but a careful examination of both banks eventually reveals two peripatus—one out on the clay, another on a mossy ledge. These are different from this morning’s find. Both have 13 pairs of legs and are coloured in three shades of brown, with diamond patterns along the back and dark patches blotching the sides. We scrabble around for litter-dwelling titbits with which to tempt one of them, hoping it will give us a shooting demonstration, but it ignores our offerings and presses on its way.
The intermediate status of peripatus—part segmented worm, part arthropod—makes them popular subjects with those speculating how one group of organisms evolves into another, and has earned them the misnomer “missing link.” The onychophoran fossil record has inspired the application of another, equally inaccurate label—”living fossil.” Surprisingly for a soft-bodied animal, fossils bearing a significant degree of resemblance to modern onychophorans have been found in deposits dating back some 500 million years or more to the Cambrian period, long before the colonisation of dry land. These early marine creatures, exhumed from as far afield as British Columbia, Utah, Germany and China, lack the characteristic head features of modern terrestrial onychophorans—antennae, mandibles and oral papillae. Some, too, are notable for being spined and armoured, unlike any form alive today. Yet in their general conformation they are tantalisingly suggestive of a line of descent to modern onychophorans
More similar to contemporary onychophorans are Late Carboniferous fossils from Illinois and France, about 300 million years old. These are associated with both marine and terrestrial fauna and flora, so may represent the earliest record of land-living peripatus. They show the banded covering of papillae and the short, cone-shaped legs of modern forms, but they have no feet, a pair of claws being attached instead directly to the trunk of each leg.
Frustratingly, the head structures are not well preserved, making it impossible to be certain about the presence of glue-ejecting oral papillae. The spitting apparatus is thought to have evolved in the first place as a defence mechanism, being adopted for attack when the animal developed predatory habits. But spitting, whether for defence or attack, would be an ineffective strategy under water, so oral papillae are considered the definitive indicator of terrestrial existence. The earliest fossil in which they appear is 20-40 million years old.
One puzzling aspect of the peripatus fossil record is that all finds have been made in the northern continents, whereas the distribution of contemporary onychophorans is predominantly southern.
Living onychophorans fall into two families: the Peripatidae, found in Mexico, Central America, northern South America, south-east Asia and equatorial west Africa; and the Peripatopsidae, represented in Chile, New Zealand, Australia, New Guinea and South Africa.
New Zealand peripatus are classified in two genera. Peripatoides is ovoviviparous—females bear live young from eggs hatched internally—while Ooperipatellus is oviparous—the females are egg-layers. Egg-laying peripatus are found only in New Zealand and Australia.
Five species of New Zealand peripatus—differentiated most readily by colour and number of legs—have been formally described. But a more complex picture is now emerging, as molecular analysis reveals a hitherto unrecognised degree of genetic divergence. Dianne Gleeson, at Landcare Research in Mt Albert, Auckland, is using DNA sequence data to determine the relatedness of hundreds of specimens from around the country and to ascertain their evolutionary origins and relationships.
“Animals that until recently would have been regarded as members of the same species because of their similar appearance have been shown to be quite distinct,” Gleeson says. “It is now clear many regions have unique peripatus, and that there are far more than five species—probably more like 30.”
The differences are not just genetic. Subtle anatomical differences have also been observed, including variations in the shape and structure of papillae on various parts of the body.
Gleeson’s work comes in the wake of similar analysis of Australian peripatus carried out by Noel Tait at Sydney’s Macquarie University. Fifteen years ago, just seven species were recognised in Australia; now the number is nearer 60 and climbing steadily. What has been regarded as one of the minor phyla, with fewer than 100 species worldwide, may turn out to be anything but.
Both my Waikaia Bush animals, I learn, are new species, yet to be named. The one with 15 pairs of legs is a live-bearer and the other, with 13 pairs, an egg-layer.
Close neighbours they may be, but it turns out the two varieties occupy different microhabitats and lead different lives. The egg-layer is found in drier conditions than those favoured by the live-bearer—hence the bare-earth environment. It also tolerates cooler temperatures, and has been found at higher altitudes. It ventures further into the open at night, too, while the live-bearer stalks its prey nearer home, within its log or among the litter close by.
In their differences these two animals reflect a wider pattern, in which reproductive strategy, environment and behaviour are interwoven. Our more open-living, cold-resistant, higher-altitude peripatus—the Tasman Glacier species being an extreme example—are all egg-layers. Live-bearers, on the other hand, opt for a warmer, more enclosed habitat at lower altitude.
For all that they are named in recognition of their Aristotelian habit of pacing about, peripatus are poor dispersers. In the course of its life, an adult female, although capable of walking many metres a night, will keep within a home range of a few square metres. Males roam more widely—they must search for mates as well as food—but their range, too, is modest. Herein lies an explanation of the newly recognised multiplicity of species.
“Put an animal that spends its life toddling between a couple of logs in a country as geologically active as New Zealand and you’ll get a lot of variety,” explains Gleeson. Seismic convulsions, volcanic eruptions, alternate periods of glaciation and warming, fluctuations in sea level—such turmoil repeatedly fragments habitats and breaks up populations. “It’s then only a matter of time before the separate pockets evolve into different species.”
Underlying the process of speciation is the practice of reproduction, and one of the most fascinating aspects of peripatus is their variety of reproductive modes. New Zealand’s velvet worms tell only half the story. Overseas there are also viviparous species, in which the embryo is nourished directly by the mother. In some of these, young develop in eggs that hatch inside the mother, but have no yolk, while in others they receive life support via a primitive placenta. As if such diversity isn’t miraculous enough, immaculate conception (or parthenogenesis) has also been documented.
Less is known about the actual sex life of peripatus. Mating has never been observed in New Zealand peripatus, so inferences have to be drawn from the few documented cases in other parts of the world. It is clear, however, that the onychophoran repertoire arnoureux is considerable.
The male of one South African species has been seen to deposit spermatophores—small sperm-containing capsules—apparently anywhere on the outside of the female. Within a week, sperm are absorbed through the female’s body wall and travel through the internal fluids to the ovaries. A number of species are though to employ this method of insemination, including New Zealand’s livebearing Peripatoides novazelandiae. The males of some other species may adopt a more conventional approach, implanting spermatophores directly in the female genital opening.
The most remarkable reproductive behaviour, however, is to be found in Australia, where the males of many livebearing species boast intriguing head ornamentation. On some, the papillae between or behind the antennae are enlarged, in the more extreme cases forming substantial pineapple-shaped edifices. On others, there is a deep pit in the skin, sometimes equipped with a formidable array of hooks or spikes.
In spring, glistening spermatophores can be observed cupped in these crowns. No-one has yet seen how they get there—contortionist feats of a high order are presumably involved—but their presence has prompted the suggestion that a male uses his head spines to facilitate the passage of sperm through a female’s skin by puncturing it. In the case of at least one species, however, the truth turns out to be even more bizarre.
While collecting specimens near Nimbin, a hippy Mecca in northern New South Wales where a marijuana festival was underway, Noel Tait found what he took to be a particularly large animal.
“But on closer examination, I realised I was looking at two peripatus, a male and a female. The male had its head, spike and all, jammed against the female’s vagina, while she held him there with the claws on her hindmost pair of legs. They continued their embrace for some 15 minutes under the microscope, and after they had separated it was clear insemination had taken place. Of course, such unrestrained sexual behaviour seemed entirely appropriate considering where we were.”
Peripatus, it appears, are as innovative in love as in war—although the court is still out on whether all such head structures are put to the same use. Nevertheless, it is likely reproduction occurs infrequently, as the chances of meeting a potential mate in the thinly spread peripatus community are slim. According to Otago University evolutionary biologist Steve Trewick, who, like Gleeson, is studying genetic relatedness among New Zealand peripatus, one impregnation a lifetime may be all some females can expect, but that could be enough.
“In the first place, a female has two uteri,” he explains. “When she’s pregnant, each uterus contains a number of embryos—at different stages of development and, if she’s been fortunate, possibly the legacy of more than one partner. In dissection, they appear like strings of tiny pearls. Secondly, females are able to store sperm and use it to fertilise their eggs long after mating. This allows them to get maximum use out of what can be a scarce resource.”
The upshot is that, despite possibly infrequent mating, females can produce numerous young. This some seem to do all year round. P. novaezealandiae females, for example, have been found to carry embryos at all stages of development at all times of year, and to give birth regardless of the season, albeit more abundantly in summer.
“There are about 16 embryos in the pipeline,” says Trewick, “and a number are born, one at a time, over a period of a day or two.”
Live-born babies emerge either head or tail first, breaking out of their egg, or thin embryotic membrane, as they do so. The first moult occurs very soon afterwards.
Until recently, there had been no reported observations of egg-laying (for which females are equipped, like insects, with an ovipositor) or egg-hatching. But researchers in Germany are now shedding light on these activities. Claudia Brockmann, a research student at Hamburg University, has been studying a number of oviparous species from Tasmania and Victoria.
In captivity, the largest number of eggs laid by a female has been 37, deposited over about two months. Brockmann says they tend to be laid singly, and laying occurs all year round. The eggs typically hatch after six or seven months—a process Brockmann has observed only twice.
“Both infants appeared back-end first,” she says. “While some legs held onto the shell and others to the soil, the body was pulled out with slow winding movements, assisted by peristaltic contractions. The animal walked backwards away from the shell, until, in one quick movement, the head popped out. The whole process took about 30 minutes.”
Newborn peripatus are miniature replicas of their mother, but usually enter the world white before gradually darkening. There is no evidence of postnatal care. Although young and mother are often found together, the pups alongside the mother or on her back, this almost certainly has more to do with maintaining humidity levels and conserving body fluid than any kind of bonding.
Sharpshooters from birth, the young fend for themselves from the word go. Within a period of weeks they disperse, competitors with their mother and one another.
In conservation terms, peripatus around the world are considered vulnerable, largely owing to pressures on the rainforest environment in which they typically live. In this, of course, they are far from alone. With the rapid disappearance of the world’s forests, countless species face extinction, many even before they have been discovered.
Part worm, part arthropod, with bizarre mealtime and bedroom manners, the peripatus is a creature that surprises at every turn. But for how much longer will it survive the pressures stacked against it? In New Zealand, only one tiny population is protected, yet it could be argued that the walking worm should be regarded as a national treasure, not an overlooked curiosity.
But the existence of so many kinds of peripatus as small, localised populations means a species can be lost through environmental damage in just one area. A South African species is thought to have perished in this way through forest fire. Such risk is all the greater because many areas in which peripatus are found have no conservation status or legal protection. In this regard, a timely precedent has been set in New Zealand, where the presence of peripatus in the suburbs of Dunedin has prompted the creation of a protected area.
Overcollection also poses a threat. Popularised as both a living fossil and a missing link, peripatus are frequently sought by universities, museums and collectors, and demand for specimens has underpinned a steady and deplorable trade in the animals. In New Zealand there are well-documented accounts of a peripatus trade which flourished into the 1970s, and Steve Trewick assures me “there are still scumbags who make money by selling peripatus.”
New Zealand’s native invertebrates as a whole are poorly served by legislation. Just 26 species of arthropod—most giant weta, a Canterbury grasshopper, a cave spider and a variety of weevils and beetles, plus the larger land snails—are fully protected by law—a serious shortcoming considering most birds, all our reptiles and our two species of endemic bat are protected wherever they are found.
Certainly, the unique features of peripatus provide compelling grounds for ensuring they have a future. So, too, does their intrinsic beauty. It is hard not to find these velveteen creatures if not appealing, at least intriguing. In all their cryptic variety, their refusal to fit the taxonomist’s pigeonhole, and their many curious ways—not least in matters of table and sexual etiquette—they give us pause for thought. Perhaps it is in exercising our minds, rather than their own sturdy little legs, that they are deserving namesakes of one of the great schools of philosophy.