Rod Morris


It’s an ant! It’s a spider. No—it’s BATFLY! A blind, wingless species of fly that lives on and with New Zealand short-tailed bats in strange symbiotic relationship. Similar animals infesting bats in South America and elsewhere are blood-sucking parasites—the vampire’s vampire—but the New Zealand version is a vegetarian coprophage specialising in the management of bat guano.

Written by       Photographed by Rod Morris

You’d be screaming too if you were this ugly and infested with batflies. New Zealand’s short-tailed bat evolved in isolation from the rest of the world’s bat community. With only birds, lizards and weta as competing megafauna, the short-tailed bat aquired some unusual habits, including a propensity to forage on the forest floor like a mouse. With the arrival of rats and other better equipped mammals and the deforestation of much of New Zealand, this unlikely bat is now rare.
You’d be screaming too if you were this ugly and infested with batflies. New Zealand’s short-tailed bat evolved in isolation from the rest of the world’s bat community. With only birds, lizards and weta as competing megafauna, the short-tailed bat aquired some unusual habits, including a propensity to forage on the forest floor like a mouse. With the arrival of rats and other better equipped mammals and the deforestation of much of New Zealand, this unlikely bat is now rare.

I was once lucky enough to spend a few nights on Little Barrier Island with a natural-history film crew. A short-tailed bat was the star of the show. It skittered around on elbows and toes, bug-hunting amongst the leaf litter. No other bat in the world hunts this way. It’s one of the things that makes the short-tailed bat a member of a rather exclusive club. You can only join if you are so far out on an evolutionary limb that you are in danger of dropping off. The kiwi clattering around in the moonlit forest that night,shrieking like adenoidal ghosts, are members too. Typically, these archaic New Zealanders behave in ways the rest-of ­the-world team thinks truly weird. Like our short-tailed bat scuttling about on the forest floor as if it was trying to reverse evolution and become a mouse.

Other archaics, some with even more startling attributes and behaviour, are less well known. Mystacinobia zelandica—the New Zealand batfly—caused a considerable flurry of interest amongst the international scientific community a few years back. E.O Wilson, the distinguished American biologist, went so far as to say that it was the fly find of the 20th century—not just a new species for New Zealand but an entirely new genus—but try asking the guy standing next to you at the supermarket checkout if he’s ever heard of it. The New Zealand batfly’s story could have contributed a hefty nugget of bizarro biology to our theme of indigenous eccentricity on Little Barrier Island that night—had we known of its existence.

Mystacinobia zelandica is a fly like no other. Not to be confused with the West Coast’s bat-winged fly—or bat-winged cannibal fly as it is more alluringly known—which boasts wings like a stealth bomber’s, the New Zealand batfly doesn’t have any wings at all. It looks more like a squished spider short of a couple of legs. Like any other fly, it has only six of these, but they’re hellishly long and bristly, with claws at the end that look as if they were meant for something. Like swimming through fur. Bat fur.

You see, Mystacinobia zelandica’s real claim to fame is that it has forged an intimate bond with one of New Zealand’s native bats, a bond unlike any other in the whole of the animal kingdom.

Entomologist Ricardo Palma of the Museum of New Zealand Te Papa Tongarewa is passionate about lice. No, really. His eyes light up as he describes the exotic skin parasites that inhabit tangled forests of fur and feathers. He recalls that some of his happiest moments were spent ex­ploring the inner space of a Japanese crow, home to some of the biggest and juiciest feather parasites you’d care to meet. The kereru, tui and silvereyes—road kill mostly—that he gets to comb through on a day-to-day basis offer compara­tively slim pickings. The trouble is, most of the passengers jump ship even before the victim’s blood starts to cool. So you’ve really got to be waiting at the side of the road with your pooter and collecting tube to stand a chance of catch­ing them before they hop off into the long grass and hitch another ride.

What appear to be strands of lichen or fungus are in fact Mystacinobia zelandica’s egg cases, the incubating stage of the fly’s life cycle.
What appear to be strands of lichen or fungus are in fact Mystacinobia zelandica’s egg cases, the incubating stage of the fly’s life cycle.

New Zealand’s only native mammals must have been even more of a disappointment to Ricardo after the furry fecundity of his native Chile. The opportunity to run a nit comb over a dead bat doesn’t come up every day, and it’s almost invariably a fruitless enterprise. Native bats were thought to have avoided fleas and other skin parasites by jumping off Gondwanaland onto Godzone before the little pests had had a chance to evolve. For a long time people just assumed that all New Zealand bats had fur that was as clean as a whistle, just like the models in the Head & Shoulders ads. But Ricar­do lives in hope. He showed me why.

The specimen he wanted me to see had been collected by zoologist P.D. Dwyer back in 1962. Dwyer had spotted a spidery-looking object about 3 mm long crawling about in the fur of a short-tailed bat he’d been looking after. At the time this weird little interloper was seen as a bit of a one-off. There was certainly nothing quite like it in all the annals of New Zealand natural history. Maybe it had come off a passing freighter, some new kind of immigrant tic that had hopped on then off the back of Dwyer’s dog. So it was stuck on a card, pushed to the back of a museum cabinet and forgotten. It would be another 14 years before anyone could put a name to it.

[Chapter Break]

Mangamuka bridge hotel lies close to the muddy river that forms one of the innermost reaches of Hokianga Harbour. By some oversight, I have never sampled its hospitality—a mistake, because the clientele of this backwoods oasis were amongst the first to learn the truth about the New Zealand wonder-fly. A framed photo of Mystacinobia zelandica—startlingly enlarged to appear several hundred times bigger than real life—used to hang in the saloon like some kind of bizarre pin-up. The story of how it came to be there begins at Omahuta Kauri Sanctuary, just up the road.

The sanctuary is one of the last mainland refuges of the short-tailed bat. In 1969 the bats were already rare enough for a newly discovered roost to warrant a mention in the Northland Times. Their home was a forest giant known as Kopi. This great kauri had attained a height of 56 m and was said to be the third largest in the country, after Tane Mahuta and Te Matua Ngahere.

When bats are active in warmer weather and the temperature in their roost is up to a steamy optimum, around 29°C, maggots emerge from these horny chambers and wriggle around in a blissful soup of bat guano.
When bats are active in warmer weather and the temperature in their roost is up to a steamy optimum, around 29°C, maggots emerge from these horny chambers and wriggle around in a blissful soup of bat guano.

During a lifetime spanning multiple centuries, Kopi had weathered many storms, even cyclones. Outwardly this colossus of the vegetable kingdom revealed few signs of ageing. On the inside it was a different story. A kauri has its own immune system. It manufactures fungicides and pesti­cides to repel unwelcome house guests, but the production process deteriorates with age. Then fungi and insects find it easier to get a toehold. Countless generations of birds and beetles chisel away, extending a growing network of nest chambers and galleries. At some point, short-tailed bats move in to set up their ideal home.

Now by our standards, short tails are not ideal tenants. For one thing they are messy defecators. The walls of their roosts are invariably coated with layers of wet and smelly guano. This must be a real booster shot for the rot that’s already extending slimy tentacles into a typical abode’s eve­ry ancient limb. Eventually the old tree’s apparent solidity becomes a façade concealing a terminally degenerative bone condition. On a beautifully calm spring day in December 1973, Kopi collapsed under its own weight.

Inspecting the site soon afterwards, an observant New Zealand Forest Service officer found the body of a short-tailed bat, killed when its roost had fallen out of the sky. He spotted two or three spidery-looking bugs clinging to its fur. Even after half a lifetime in the Forest Service, he had to concede that these unappetising-looking little aliens were a new one on him. Diligently, he packed them in an old to­bacco tin so the experts in Auckland might identify them.

[Chapter Break]

Bev holloway was the first New Zealander to gain a PhD in biology at Harvard. In 1962, with her doctorate under her belt, she returned to New Zealand and took up a post with the Entomology Division of the Department of Scientific and Industrial Research (DSIR), in a section headed by husband-to-be Dr Willy Kuschel. Sitting in their airy Lynfield bungalow, in west Auckland, the couple speak fondly of their early adventures together, exploring the remotest corners of the country. The 1960s and ’70s were heady days for young biologists. The bush must have seemed brimming with possibilities—new species to be discovered and the chal­lenge of a vast ecological jigsaw puzzle to be resolved. But the discovery that was to bring Bev international scientific acclaim wasn’t the fruit of weeks of tramping through un­charted bush. It arrived in a Jiffy bag a day or two after a big old tree had fallen over in Northland.

Most of us wouldn’t be especially pleased to get some­thing in our morning post that had crawled off a dead bat. The contents of the old tobacco tin had ripened on the journey from Kaitaia, cranking up its bat-scented muski­ness. The pungent little critters that confronted Bev were as unfamiliar to her as they had been to the Forest Service officer who had scooped them up. But research soon led her to discover that they bore a strong resemblance to a tribe of blood-sucking flies that plagued the unfortunate bats of South America.

The lazy option would have been to assume that the beasties from Omahuta were the New Zealand end of the same family. They were comparable in size and general appearance to the South American batflies. The Latinos were wingless and spidery with poor eyesight and long bristly legs, each terminating in a pair of highly specialised claws, just like the kiwis, but that was where the similari­ties ended. Bev’s meticulous forensic analysis of the bodies was the first step on a journey that would ultimately bring Mystacinobia zelandica to the attention of the international scientific community—which would be gob-smacked.

Batflies from other parts of the world—such as these golden batflies from New Caledonia—are winged and have a much larger thorax containing muscles for flight.
Batflies from other parts of the world—such as these golden batflies from New Caledonia—are winged and have a much larger thorax containing muscles for flight.
Like most insect larvae, they bear little resemblance to adults.
Like most insect larvae, they bear little resemblance to adults.

You can tell a lot about an animal’s lifestyle by having a really good look at its gobbling equipment. With their stiletto-like cutting gear, the mouthparts of the South American batfly were clearly adapted for piercing skin and sucking up blood. But the Omahuta batflies lacked this kind of miniature vampire toolkit, and Bev’s examination of the little fellow’s gut contents revealed no trace of partly digested bat blood. What she did find was pollen from Freycinetia and other native plants, which the bats them­selves were known to feed on.

It was hard to accept that if every other batfly in the world was a blood-feeding parasite, the Kiwi batfly could really be a pollen-guzzling vegetarian. And if it was, how did it reach its food supply? Flightless and almost blind, it wouldn’t have a hope of getting to the blossoms unaided. Could the batflies be hitching a ride to their feeding grounds with the bats? And if so, what, if anything, was in this arrangement for the bats? Many more unanswerable questions began to occur to Bev. What she needed to an­swer them was more batflies, preferably alive and in the company of bats.

It was now some weeks since Kopi had collapsed, but the knowledge that short-tailed bats were reluctant to abandon a roost even after the host tree had fallen seemed to offer a faint hope of getting a first look at a live batfly. Unfortunately, by the time Bev and the rest of a DSIR special investigation team reached the kauri sanctuary, all the sur­viving bats had bailed out of their old home.

[Chapter Break]

They had, in fact, relocated themselves 8 m up in anoth­er ancient kauri nearby, but they might as well have moved to the moon. The scientists—a mix of entomologists and bat specialists—had democratically decided that causing any further disturbance to the endangered tree-dwell­ers couldn’t be justified. Not for the sake of a mere bug. Perhaps the decision reflected a bias in the value system of humanity at large in favour of the be-titted of the world­ mammals if you like—a bias which must be a constant source of frustration to bug people, frog people, chook people and the rest. As it turned out, however, Bev didn’t have to return to Auckland completely empty-handed. From Kopi’s hollow trunk the team recovered a huge ac­cumulation of bat guano, bits of dead batfly and a number of what looked like peculiar little seed pods on long horny stalks.

After many weeks puzzling over the more obvious batfly remains, Bev turned her attention to the mysterious seed pods. At first she thought they might be the indigestible parts of some fruit or other that the bats fed on. But as she teased one of them apart under a dissecting microscope, a tiny larva wriggled free. It was quite a surprise. She re­calls how at that moment the peace of the laboratory was shattered by a certain amount of triumphant yelling and whooping. After all, though a mere infant, this was Bev’s first live Kiwi batfly.

The arrival of  Cyclone Allison one year later,on March 12, 1975, brought about a further dramatic change of fortune for Bev and her fellow entomologists. Rain was falling at a rate of 40 to 70 mm per hour in some places. Parts of State Highway 1 and the South Island Main Trunk railway line were washed out or buried under metres of gravel. One diesel locomotive was stopped in its tracks and partly buried by debris flows. When Allison moved north and raged through Omahuta, it soon became apparent that the bat colony had made an­other bad choice. The Second Bat Tree, as it was known, fell on March 14.

With winter on its way, there was deep concern for the bats. Short tails become torpid in cold weather. Under normal circumstances they would have been insulated from the worst effects of the cold, but with their roost on the ground and shipping water, they were extremely vul­nerable. If they didn’t drown or die of hypothermia, they could be devoured by rats. When the bat specialists began talking up a rescue operation, Bev saw her chance. The Entomology Division joined forces with the Ecology Divi­sion, the Forest Service and the Department of Internal ,Affairs giving the entomologists a golden opportunity to see live batflies and get a glimpse of their behaviour in the environment of the bat roost.

The highly social behaviour of the bat is tailor-made for social insects like the batfly. Rather than infesting a single animal, batflies infest the roost, moving freely between their hosts. Despite this, each bat appears to bear a half-dozen or more mainly gravid females, ensuring that if it leaves the nest and does not return, it will bear a cargo of immigrant batflies to its new location.

The main aim of the rescue operation was to transfer some of the bats to a man-made roost in a nearby kauri in the hope that this would encourage the rest of the colony to abandon the Second Bat Tree. Willy Kerschel organised the cutting of a wedge from the top of the natural roost with a chain saw. Remember that short-tailed bats are messy defecators: the panic induced when the chainsaw started up wouldn’t have improved sanitary conditions within the chamber. Given, too, an internal temperature maintained at a funky 29° C by the heat given off from hundreds of bat bodies, you can imagine the smell that began to emerge as the chain bit into the hollow of the trunk. Bev and her team were undeterred. They were about to get their first glimpse into a short-tailed bat roost.

It was a startling scene. A seething mass of batflies con­ducted battalion-strength manoeuvres across the darkling plains of the roost’s inner walls. Here and there were great clusters of egg cases, their long respiratory horns forming spiny thickets like the military “hedgehog” of Alexander the Great’s spear-carriers, a defensive strategy for use against charging cavalry. In many places the interior terrain was slick with guano. Thousands of larvae writhed about in foe­tid swamps of bat poo. But far from writhing in agony they were in fact lovin’ it. It seemed that the pungent brew of pre-digested fruit pulp, pollen and yeast was ambrosia not just to the larvae but to the whole fly whanau.

What the team were witnessing lent vital support to Bev’s idea that the New Zealand batfly wasn’t a vampire in the South American tradition. New Zealand’s Mystacinobia was a coprophage—a poo-eater. And the walls of the roost were coated with enough bat guano to feed an army of 10,000 batflies.

But now the temperature of the newly opened roosting space was falling, and this seemed to be having an unset­tling effect on the inhabitants. A mass migration towards the opening began. Wave upon wave of batflies came scut­tling out into the light. Like little heat-seeking missiles, they homed in on the bat rescuers, burrowing deep under clothes and lodging in the most intimate of bodily crevices to keep warm. It was not a comfortable feeling. At that stage, despite Bev’s assurances concerning the benign anat­omy of the little beasts’ mouthparts, her colleagues weren’t entirely convinced the batflies didn’t possess some secret weapon. But in a demonstration of quite outstanding sang­froid, everyone carried on working until phase one of the rescue had been completed. The cut wedge of old roost and a small advance party of bats were transferred to the new tree. Now it was up to the bats.

[Chapter Break]

Back at Mangamuka Bridge Hotel, the bar remained deserted while the rescuers tried to dislodge clinging batflies in the privacy of their rooms. Many fine specimens were harvested for the ento‑mologists’ collection before supper that night.

Two days later the rest of the bat colony—several hun­dred animals—emerged from the stricken kauri. The rescu­ers’ cunning plan had worked. But don’t forget: batflies are flightless. When a short-tailed-bat colony abandons a roost like this, any flies left behind are doomed. As the tempera­ture falls and their food supply runs out, they face certain death. But when some of the exiting bats were trapped in mist nets, on close inspection every single one was found to be airlifting at least half-a-dozen batflies. By burying them­selves deep in their hosts’ silky fur, the stowaways seemed to be trying to maximise their chances of surviving the jour­ney to the bats’ new home.

More than 80 per cent of these transit batflies were found to be female, most of them fully gravid and each capable of laying about 30 eggs. Now batflies have no way of predict­ing when bats are about to split. Their insurance policy ap­parently consists of a corps of gravid females on permanent standby, accompanying their hosts on every sortie. Should any bats take it into their heads not to come home one night, these hitchhikers are ready to become the founders of a new batfly colony.

For a few hundred of the batflies that missed out on this particular airlift, the outcome wasn’t so bad either. They lived out the rest of their lives inside a large plastic laundry bag fitted with ventilation panels, a cosy Tupperware box taking the place of the roost’s inner chamber. This captive colony was so precious that nothing less than 24/7 personal care would do, so Bev decided that its new home would be her airing cupboard. The thermostat was adjusted to 29° C to mimic the conditions inside a bat roost. Instead of bat guano, her new housemates were treated to as much mashed banana and yeast as they could eat. It was pretty much a holiday camp for batflies, but Bev’s work had only just begun. Each day, after the breakfast dishes had been cleared away, the kitchen table became Bev’s laboratory bench—Mystacinobia zelandica’s Formica launch pad to in­ternational celebrity.

One of the first things Bev noticed about the colony was that it was far from being a homogenous group: its members didn’t all look the same and they came in a range of sizes. Males and females looked so different from each other that one Japanese expert, when sent some of the Kopi specimens, suggested they were different species. Males were generally bigger than females, and some of the big­gest and beefiest appeared to live beyond their reproductive phase and take on the role of soldier or guard.

The relationship between bat and fl y might confer mutual benefits, but the relationship between bat and tree is more one-sided. Short-tailed bats select hollow forest giants—such as aged kauri—for roosts. These older trees are susceptible to attacks by fungi, moulds and boring insects and their predicament is not helped once prolific guano and the heat from roosting bats is added to their body cavities.

Every morning as Bev removed the Tupperware box containing the colony from the big laundry bag in the air­ing cupboard, she would be greeted by an angry whine “like a high-speed dentist’s drill”. Later she found she could elicit individual performances by picking up the largest males with a pair of forceps. These guys had huge thoracic muscles that you would expect to have atrophied given they were no longer used for wing-flapping. It was almost pathetic to see their owners getting themselves all pumped up, vibrating away at about 1000 rpm as if preparing for take-off, when all they could do was sit on the runway and shrill. What good did it do them? When Bev asked herself this question, she had already realised that anything to do with the way a batfly behaved had to be considered in the context of its relationship with bats, fine-tuned over mil­lions of years.

Accordingly, Bev read every scrap of information she could find on short-tailed bats and came up with this nug­get in a letter written by Mr H.E. Grubner of Whakatane to a Miss Karen France on March 6, 1959. Grubner had kept a short-tailed bat in captivity for several weeks in Oc­tober 1958 before putting it on a plane to Auckland Zoo.

“I should mention that certain sounds such as a car starting up although not close would put the bat into a pan­ic,” he had written. “I remember that one woman’s voice seemed to frighten him every time she spoke and he would take off with a rush although others had been speaking before with no apparent notice taken. Static on the radio and the bat was off every time. I hate to think of the panic when the plane took off.”

Bats, he was suggesting, were very sensitive to certain sounds.

Now given that a bat’s diet included insects as well as nectar, fruit and pollen, Bev was led to consider whether a succulent batfly might not be a tempting proposition; yet she’d found no digested batfly remains in the mountains of guano she’d trawled through. Could it be that a big male batfly’s job was to “yell” a warning to remind bats to tread carefully around the batfly colony and resist the temptation to nibble its residents? Bev thought so. At the same time, the hefty lookout was probably telling its fellow batflies: “Stand clear. Big clumsy warm-bloods coming through.”

Bev had already seen, in the Second Bat Tree, how females deposited horny egg cases in large clusters. The dense spiny thickets so formed could be another way of de­terring reckless bat-traffic around the nursery, and further evidence in support of the idea that the need to neutralise the threat of predation by bats was the rocket fuel driving the engine of batfly evolution.

[Chapter Break]

As she monitored the day-to-day activity of the captive colony, Bev found that males and females of all shapes and sizes mixed freely, and that all the adults, regardless of sex, seemed to take their turn at attending to the needs of the larvae. Compared with your average housefly, which mates with a complete stranger before the female abandons her several hundred offspring on something deeply unsavoury, the batfly looked very civilised indeed.

This wasn’t the only evidence of a sophisticated structure within batfly society that Bev observed. There was a very high level of interaction between all the nest-mates—young and old were constantly stopping to groom one another or to offer choice titbits of food. Bev thought the intensity of this behaviour highly suggestive of some kind of communication, possibly a chemical-information exchange of the kind that occurred in a beehive or ant colony. In mam­malian terms, this would be on a par with a bunch of tree shrews inventing the internet. It would certainly help to explain how the batflies synchronised egg-laying and nu­merous other activities that depended on a significant level of co-operation.

The bat’s life cycle helped to explain another little mys­tery. Bev’s dissection of one of the Kopi “seed pods” had shown that batfly larvae could survive many months of ad­verse conditions inside their horny egg cases. They seemed to be able to put their development on hold, entering a kind of suspended animation. But why would they need to? Bev surmised that it was an over-wintering strategy. To survive the cold season, the bats became torpid, allowing the tem­perature within the roost to fall. Few of the adult batflies survived, but as soon as the forest began to warm up again and the bats resumed normal operations, a new generation of batflies was all set to emerge from the eggs.

The bat–batfly relationship is far from being one-sided. Bev thinks that the flies’ presence in the roost could be a big plus for the bats. The insects clean up after their messy hosts, consuming large quantities of bat guano. They may even help to keep the bats fur clean by combing out stray bits of dinner with their specially adapted claws. A relationship like this between very different animals is so unusual it doesn’t even have a name yet.

Willy Kuschel has told me he sees batflies as living proof that the evolutionary toolbox inherent in the genes of every living organism comes equipped to fulfil an almost infinite variety of destinies. Ironically, though, extreme specialisa­tion could prove the batfly’s downfall. Having sacrificed its eyesight and ability to fly, it is entirely dependent on bats for food and transportation. Furthermore, batflies can survive only in the unusually high temperatures maintained inside a bat colony. Like many other extreme specialists, the batfly may have painted itself into a corner. It seems that just as the short-tailed bat is now the only surviving member of its family, Mystacinobia zelandica, the Kiwi wonder-fly, is the only living member of the Mystacinobidae.

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