Scientists recently announced they had found an enormous new stick insect in Australia. At 41cm in length and weighing 44g, the main question I heard was: “Why didn’t scientists notice something that big before now?”
The short answer is: it’s a stick. Stick insects spent over 100m years perfecting their cosplay as leaves, branches and moss. They are diabolically difficult to spot, even with fairly acute human vision. If you disturb a stick insect, its usual response is to fall to the ground and lay still. So now you are looking for a stick lying on the ground … among all the other sticks.
Scientists were alerted to the presence of this new insect, Acrophylla alta, by a photo posted on iNaturalist, the community science sharing site. Based on that image, they spent several nights tramping through a rainforest with headlamps and flashlights, hoping for a glimpse of this rare new beast. They eventually located and knocked the stick insect off of its perch, which can be 30 metres up in the tree canopy, with a long (actual) stick.
Phasmids (stick and leaf insects) are an incredible example of natural selection at work. As herbivores quietly munching leaves, stick insects are a delicious snack for many other animals. Evolution shaped the 3,500-plus described species of phasmids into stunning examples of camouflage, usually by pretending to be objects that are irrelevant to predators: sticks, bark and leaves. They solved the problem of hiding in plain sight through a variety of forms most beautiful and wonderful; their bodies range from long skinny tubes to wide and flattened leaf shapes.
Stick insects are grouped into delightful categories with names like broad prickly sticks, winged bark huggers, stout crawlers, narrow leaf mimics and tree lobsters. The last is a group best described as insects that gave up on the whole delicate leaf and twig act to become heavily armoured, spiny tanks – determined to make a predator profoundly regret ever trying to eat them.
As a former keeper of stick and leaf insects in a bug zoo, I can attest to just how good these animals are at being invisible. Even when you knew there were exactly 10 leaf insects in a cage, finding numbers 9 and 10 always involved a long manual search of every single branch and leaf, sometimes requiring multiple people. Jungle nymphs (Heteropteryx dilatata) are 17cm lime-green spiky monsters that somehow manage to disappear into foliage despite their size. Often you only discovered one by getting a painful kick from a spiny leg.
The recently described Australian stick insect also lives in a rainforest tree canopy, so it’s not surprising it remained hidden for so long. Insects and their relatives are the animals science knows the least about, despite being some of the most abundant organisms on Earth. After almost three centuries of taxonomic research, scientists have only described and named about 1m insect species; thousands of new species are added to that total yearly.
This Acrophylla alta is 41cm long and weighs 44g. Photograph: Professor Angus Emmott, James Cook University/Reuters
The question is not why weird new insects keep getting described by science, but why there aren’t more strange insects, spiders and other relatives with extra legs being discovered daily. Research suggests that at least 5m insect species exist, and insects and their relatives (arthropods) make up 85% of all known animal species. To put that in context, there are as many species of just ladybirds as there are of all mammals combined.
The International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species is a good benchmark to get a sense of how little we know. IUCN is the primary information source on the global conservation status of animal species, but its database lists only 1.3% of known insect species for evaluation. For the entire category of insects, the most species-rich animals on our planet, IUCN’s data table simply says “insufficient coverage”. It simply doesn’t have enough data to estimate the percentage of threatened insect species.
Naming and describing is just the first step of understanding and preserving our biological diversity. For many species, we have no idea where they live, what they eat, or what their lives are like. Of the insects listed in the IUCN database, 26% are listed as “data deficient”. This adorable little willowherb leafcutter bee is extinct in the UK, and we don’t know enough about it to say much more than that.
By focusing on large, charismatic animals, we miss understanding the little animals that run our world and provide essential ecosystem services. It’s little invertebrates that pollinate plants, feed birds and other animals, and keep soils healthy. They deserve to be studied as much, or more, than their bigger vertebrate kin. Concentrating on common threats to animals, big and small, can help us make better choices about prioritising research and conservation.
