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.
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.
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”.
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.