flightless

Stick Insects

Stick insects are often overlooked, and that’s the way they like it.

New Zealand is home to a wide variety of stick insects, from the horrid stick insect (Argosarchus horridus) with a body as long as your hand, to spiky creatures smaller than your little finger. Most species of stick insects are found in the tropics, so it’s peculiar for a cool-temperate country like us to have so many, even a mountain stick insect (Mimarchus tarsatus) that lives in South Island tussock that’s covered by snow all winter.

1. prickly stick insect

Prickly stick insect (Acanthoxyla prasina).  Photograph: Alan Gilchrist.

Although they’re relatively common, stick insects excel in hiding. Our New Zealand species are flightless and defenceless. If discovered, they will sway gently like a twig in the breeze, or drop comatose to the ground, where can lay immobile for up to half an hour before reviving and climbing a tree again. The best way to find them is by beating. Hold a white sheet or umbrella under a tree or shrub and hit the branches sharply with a stick and down they’ll drop. Over the last few months the Whanganui Regional Museum has been doing that on field trips around Whanganui and the Manawatū, and we now have a half dozen stick insects of different species, sizes and colours in captivity.

Stick insects are easy to keep. They only need a regular supply of green leaves (pohutukawa seems to be a favourite) and an occasional spray with a plant mister. They’re happy to be handled, and are a great “gateway insect” for children who might be nervous about handling a creepy-crawly, as they’re completely harmless. They spend most of their time slowly munching on leaves and laying eggs.

2. stick insect cage

Stick insects live happily in a cage as long as it’s not too hot and dry, and there’s a constant supply of fresh leaves. Photograph: Whanganui Regional Museum.

It’s possible to breed stick insects even if you only have one, because some of the most common species, the spiky stick insects (Acanthoxyla), are parthenogenetic. This means that no males are needed, with mothers laying eggs from which hatch only daughters. In fact, until this year, no males had ever been seen. Then one was found, in England of all places. The species had been introduced to England in the 1920s and is doing well. Males seem to be very rare mutants, not required for reproduction.

Because some stick insect species have just one sex and others have both, their genetics are very interesting to entomologists. Studying their DNA has also revealed unknown species hiding in plain sight. One of the new species was recently given the scientific name rakauwhakanekeneke, te reo Māori for “the stick that walks”.

3. stick insect eggs

If kept in a damp dish, but not allowed to go mouldy, stick insect eggs will hatch after a few months into tiny versions of the adults. Photograph: Whanganui Reigonal Museum.

The stick insects in captivity in the Museum have been growing steadily, and we’ve collected dozens of eggs, which are currently incubating. The hatchlings will be released back into the bush. Unfortunately, stick insects have a short life expectancy. They hatch in spring, reach full size in a few months, and usually don’t survive the winter. When ours die, we’ll preserve the bodies and put them on display in a new insect exhibition ready for when the Museum re-opens in October. Visitors will be confronted by a case full of sticks and invited to work out how many of them are insects.

 

Dr Mike Dickison is the Curator of Natural History at Whanganui Regional Museum.

Advertisements

The Mysterious Adzebill

New Zealand was once home to many flightless birds. Some, like the moa, are well-known, but others, like our flightless ducks, geese, and owlet-nightjar, are familiar mostly to palaeontologists. One bird that deserves to be better known is the mysterious adzebill.

1. Adzebill Martinson

A North Island adzebill (Aptornis otidiformis) eyes up a tuatara in a 2005 painting by Paul Martinson.
Photo: Te Papa / CC-BY-NC-ND

There were two species of adzebills, Aptornis otidiformis in the North Island and Aptornis defossor in the South. Both were huge. When their bones were first discovered, they were mistaken for a small moa. Fully-grown birds would have weighed perhaps 20 kg, larger than a swan or pelican.

Adzebills had massive heads with heavy down-curved beaks. The beaks tapered to a point, and Dr Richard Holdaway, who coined the name “adzebill”, once confessed to me that “pick-bill” would have been more accurate. The robust vertebrae in their neck would have anchored strong muscles and allowed them to deliver a powerful blow.

These birds also had massive feet, with strong tendons, that would have made them good at digging. For some time biologists debated what they ate. Did they dig up roots, pluck leaves or break apart rotten logs? Their beak wasn’t hooked like a bird of prey.

A technique called stable isotope analysis which lets us analyse animals from the composition of bone – you are what you eat – revealed that adzebills were carnivores. We can imagine them tearing open trees for huhu grubs, plucking lizards or baby birds off the forest floor, digging up giant earthworms, and excavating tuatara, or even nesting seabirds, out of their burrows.

A second mystery was what adzebills were, exactly. They didn’t resemble rails like the weka or takahē, and for some time were put in their very own family. Some ornithologists thought their closest relative was the flightless kagu of New Caledonia. Others thought it belonged with chicken-like South American birds called trumpeters. The debate continued fruitlessly for decades.

Alex Boast is a PhD candidate at the University of Auckland, working on ancient DNA. Improved techniques now allow us to recover and examine fragments of DNA from bones and eggshell of extinct birds, not enough for Jurassic Park cloning, but enough to construct a family tree and determine their nearest relatives. Alex analysed adzebill DNA and compared them to numerous other birds, and the results suggest that adzebills are not kagus, or trumpeters. They are flufftails.

2. Flufftail Keugelmans

The white-spotted flufftail (Sarothrura pulchra), painted by John Keulemans in 1894. This delicate little bird seems to be the adzebill’s closest living relative.
Ref: Wikimedia Commons

Flufftails (nine species in the genus Sarothrura) are secretive ground-dwelling birds about the size of a starling, rusty brown and spotted. They do indeed have fluffy tails. What’s unusual is that flufftails are all found in Africa, and on the island of Madagascar, nowhere near New Zealand.

Africa and New Zealand were once connected as part of the supercontinent Gondwana of course, and fossils tell us that adzebills have been here for millions of years, plenty of time for their ancestors to get here and evolve into a giant flightless predator. Intriguingly, the kiwi seems to have done the same thing. Its closest relative is another African species, the elephant bird of Madagascar. The difference is, while one flightless bird survived the arrival of human beings and became the symbol of New Zealand, the other was wiped out. The not-so-mysterious adzebill is now mostly forgotten.

 

Dr Mike Dickison is curator of natural history at the Whanganui Regional Museum.