New Zealand's flightless hitch-hiking bat-fly!

This series was created in conjunction with Auckland Zoo ectotherm keeper Ben Goodwin, to shine a light on Aotearoa’s precious native invertebrates and discuss the actions we can all take to help them.

Bats have long interested humans, and so they should. Not because they’re ‘scary’ blood-sucking vampires, but because of the vital role they play in our ecosystems. There are over 1,100 species of bat around the world that help to pollinate plants, fertilise the ground and disperse seeds.

In fact, more than 530 species of flowering plants rely on bats to pollinate them, either partially or exclusively. Some of these plants are agave (which are harvested to supply the multimillion-dollar tequila industry), bananas, and balsa trees (which produce the world's lightest timber). In fact, the relationship between bats and agave are so strong that bat populations will fluctuate in size in accordance with the success of agave!

They’ve also evolved some incredible abilities, like being able to locate their food by bouncing sounds off the objects around them (echolocation) and slowing down their metabolic rate so they can hibernate in colder months when food is scarce (torpor). In New Zealand, they’re our only native land mammals and there aren’t many of them left – so what does that mean for the New Zealand bat-fly who has specially adapted to co-exist with bats?

New Zealand has three native bat species or pekapeka: the long-tailed bat (Chalinolobus tuberculatus), the lesser short-tailed bat (Mystacina tuberculata) and greater short-tailed bat (Mystacina robusta), and none of them are thriving. The long-tailed bat is nationally-critical (the highest threat classification in the New Zealand threat classification system), the three sub-species of lesser short-tailed bat are either at-risk or vulnerable; and the greater short-tailed bat was last sighted prior to an invasion of ship-rats on Taukihepa (Big South Cape Island), near Rakiura (Stewart Island) in 1967 and is now thought to be extinct.

So, what of the insect species whose fate is linked to the lesser short-tailed bat? The New Zealand bat-fly (Mystacinobia zelandica) is cold-sensitive, blind, unable to fly and feeds only on the guano (poo) produced by the New Zealand short-tail bat which it relies on to create the warm temperatures it requires to survive and breed. This kind of commensal relationship occurs when one organism derives food or other benefits from a larger organism without hurting or helping it (like the bacteria which lives in your mouth, a clownfish that lives within an anemone, or the sucker fish which cling onto sharks!) – which as these relationships go, is a relatively benign interaction.

But how do you learn about a 3mm-sized animal that spends its life high up, in a hole, in a kauri tree or flying through the night clinging tightly to bat-fur? Our native bat-fly was virtually unknown to science until 1973. That’s when biologist Dr Beverley Holloway received an old tobacco tin in the mail with a few dead specimens inside. These specimens were found in Omahuta Kauri Sanctuary when ‘Kopi’, a 56-metre giant kauri, collapsed under its own weight and a whole colony of 500 short-tailed bats were displaced from their roost. Arriving at the scene, New Zealand Forest Service officers spotted several ‘spidery-looking’ flies clinging on to a dead short tailed bat - and it was this find that kick-started research into this species.

At the time Dr Holloway worked for the Entomology Division of the Department of Scientific and Industrial Research (DSIR) and she got to work investigating the bat-fly specimens. Inspecting the contents of their stomachs she found pollen and guano instead of the blood that would have been expected if the insect was a parasite, and the morphology of the mouth parts were also not consistent with a blood-sucking mammal. In 1974 several trips were made to the sanctuary by Dr Kuschel with other staff from the Entomology Division, they returned to the site of the fallen kauri to discover a bat roost with walls covered in bat guano, bits of dead bat-fly and bat-fly larvae – but unfortunately no live bats or bat-flies.

It wasn’t until Cyclone Allison hit Omahuta in 1975, causing damage to a second kauri tree (which the bats from Kopi had moved into) that Dr Holloway joined a government-backed bat rescue operation and was able to witness a live bat-fly colony in action – thousands of batfly eggs, larvae, puparia and adults. She was then able to collect live specimens that would travel home with her and live in her airing cupboard, these were crucial to recording their natural behaviours. Kept warm (about 30c) and fed a diet of banana and yeast, the larvae were able to continue their development without their bat hosts.

Dr Holloway found that the New Zealand bat-fly was not a parasitic bloodsucker, but in fact a coprophage (poo-eater) and did not have the modified mouthparts required for piercing skin. Not being able to fly itself, the New Zealand bat-fly has claws adapted for movement over fur, which they can also use to catch a ride outside the roost! Gravid females (those carrying fertile eggs) will accompany bats on their nocturnal feeding expeditions with a clever evolutionary purpose. Should this bat decide to relocate and not return to its original roost, a new colony of bat-flies can be set up at a new location.

“The need for unusually high temperatures and a yeasty diet combined with the loss of flight has resulted in the flies becoming totally dependent on the bats… The total dependence of Mystacinobia [the bat-fly] on Mystacina [the short-tailed bat] for food, shelter, and dispersal suggests a very long association between the two, perhaps predating the arrival of their ancestors in New Zealand.” – Dr Beverly Holloway, 1976

In order to share a co-dependent life with an insect-eating bat these flies have evolved extreme specialisations; males are capable of creating high, shrill sounds which are thought to cause some discomfort to the bats and prevent predation – which is key when you’re sharing the same home. In winter when entire bat colonies enter a state of torpor, and the temperature within the colony drops, the bat-fly larvae are able to slow their development, waiting until the bats become active again and temperatures increase before continuing on with their life-cycle. Perhaps the most unusual adaptation of the New Zealand bat-fly is their social interactions. Bat-fly generations overlap, meaning that the adult flies live with and amongst their own progeny. Adult flies and larvae are also known to mutually groom each other – a behavior most often associated with primates, not flies. 

This video from Te Ara shows a female fly depositing her eggs close to a newborn bat. When the eggs hatch, the batfly larvae are then able to attach themselves to the baby bat’s skin. 

We can protect the bat-fly by protecting New Zealand’s lesser short-tailed bat. Our native bat species face very similar threats to Aotearoa’s endemic birds such as predation by introduced species like stoats and feral cats and habitat loss through forest clearance, for the bats (and therefore the bat-flies), large, old forest trees, such as kauri (Agathis australis) and northern rata (Metrosideros robusta) are critical for their survival.

Every 4-6 years mast-seeding events happen in New Zealand where trees of certain species (such as New Zealand flax or beech trees) synchronously and abundantly flower, producing a glut of fruit which is beneficial to indigenous fauna. Unfortunately, this increase in food supply also triggers a dramatic increase in the numbers of introduced predators like mice, rats and stoats. Research by New Zealand’s Department of Conservation (DOC) has found that during these rat-plagues native bat deaths increase by 20% as rats will climb trees to get to native bats as well as lizards and birds – and presumably insect populations suffer even worse.

Auckland Zoo was home to a colony of rare Waiohine short-tailed bats from 2007 – 2013 who spent some of their time in the Night forest aviary in Te Wao Nui. This 12- strong bat colony arrived at the zoo following a wild translocation attempt managed by DOC. Affected by a disease of unknown origin which damaged their ear pinnae, this created concern from experts that they may no longer have been able to echo-locate to find food, and likely would have died if they were not rehomed.

Initially these bats were translocated from Pukaha Mount Bruce to live on Kapiti island to create an insurance population for their species. This is so that, in the event of a man-made or environmental disaster, there would be a viable second population of these bats in New Zealand. Once it was found that this colony was not able to survive in the wild, the Department of Conservation, Auckland iwi Ngati Whatua and iwi partners Kahungunu consulted and brought these bats to Auckland Zoo to be cared for.

Bird keeper Debs has fond memories of this time and describes these bats as “such unique creatures”. It has been a highlight of her career learning about how to care for this species and even hand-raised two small bat pups that were born at Auckland Zoo – the first time this endemic New Zealand species was bred and hand-reared in a zoo environment. When it was confirmed that the pups were losing weight and their parents were not able to successfully raise them, the bird team and Debs stepped in to help. Each bat was born at an amazing 4 grams each and were raised to the age of 10 months before being successfully reintegrated with the adults.

Sadly these bats did not survive, but this experience was not in vain. We can draw upon the valuable knowledge that was learnt at this time to assist wild bats in the future. While parent rearing would be preferred for future breeding events, the experience has confirmed our ability to rear pups if intervention is ever required.

Recently Debs was able to contribute information about bat husbandry and reproduction in a Veterinary Care manual for New Zealand bats. This guidance document was compiled by senior ecologist and bat specialist Dr Kerry Borkin from Wildland Consultants Ltd, that will help kiwi conservationists in their future endeavours.

As bats now remain in only a few areas of native forest, it’s important that these forest areas are protected. Dr Colin O'Donnell and our conservation partners at Department of Conservation (DOC) have been using traditional rat trapping techniques, alongside larger-scale 1080 efforts in recent years, in order to stem the decline of bats in these areas. In areas that are large and difficult to canvass by foot, 1080 use has seen a marked improvement for bats over traditional rat trapping. 

Our special thanks to Manaaki Whenua - Landcare Research for allowing us to take photos in the New Zealand Arthropod Collection.

If there is a species you’d like us to cover in a future invertebrate blog, drop us a line at zoonews@aucklandzoo.co.nz.