If someone asked you to describe a stick insect in general terms, you would probably talk about a creature disguised by nature to look like a stick. After all, that’s where the name comes from. You wouldn’t expect an insect of unusually large size or one that sports a bright blue colour. And yet that is exactly what a team of scientists has found on Madagascar.
Madagascar has long been known as one of the world’s most bio-diverse islands. So few are surprised when new species are found there. But ‘surprise’ was the key word for German scientists who recently discovered two new species of stick insects. Both are exceptionally large, and both feature males who change colour when they reach sexual maturity.
Their different colours are not just different shades of green and brown. The males of one species turns a bright blue that easily sticks out to predators. The male of the other species turns a variety of different colours. Neither one can easily protect itself through camouflage once sexual maturity has been reached.
Survival by Camouflage
If you keep stick insects as pets, you know how effective their natural camouflage is. You could stare at your enclosure for hours and never see your stick insects because they blend in so well. This natural camouflage is key to their survival. So why would nature produce two species of stick insects that seem so easy to spot?
There is no way to answer that question for certain, but the same German scientists who discovered the two new Madagascan species have surmised that their lack of natural camouflage may not be all that bad. There could be some benefits to being bright blue, for example.
Survival by Toxins
It is clear that stick insects are not aggressive creatures looking for a fight. They prefer to run and hide rather than stand their ground. In the case of predation, there is not much a stick insect can do once discovered by a predator. But perhaps the newly discovered stick insects have another weapon up their proverbial sleeves.
Researchers surmise that the bright colours the males sport in maturity are the result of an accumulation of certain toxins in their bodies. The substances are not toxic to the insects themselves, but they are to predators. If this is truly the case, it would not be the first time such a natural defence was observed in the wild.
Almost all species of stick insects have glands in the neck that produce toxins. Some species even display those glands in bright colours when threatened. It could be that a build-up of toxins in the new species creates the bright colours as a warning sign to predators to stay away.
The researchers say this sort of thing has already been observed in several different species of Madagascan frogs. The frogs in question are naturally camouflaged under normal circumstances. When threatened however, they can plump themselves to reveal the bright colours that act as proof of the toxins in their bodies.
Right now, researchers do not know if the toxin theory is correct. But they are committed to continuing their research in order to find that out. If what they surmise is correct, it could explain why these brightly coloured males are not afraid to move around while searching for a mate.
Attracting a Mate
Another thing that researchers are curious about is the actual biological function of the bright colours. It doesn’t seem reasonable that the colouring would be purely a defensive mechanism. Otherwise, there would be no need for it. Natural camouflage would do fine on its own.
It could be that in these two particular species, the bright colours also double as a way of attracting mates. We already know that most species of stick insects have the ability to reproduce with or without participation from males. In other words, females can lay unfertilized eggs that essentially become clones at full maturity. Eggs fertilized by males end up creating entirely new insects with separate genetic makeups.
Perhaps the bright colouring observed in these two species is a way to help females find males whenever they’re ready to fertilize their eggs. This could be a way to more equally balance out the clones versus the genetically new insects by encouraging females to fertilize more eggs than they otherwise would.
Researchers bred the newly discovered insects in captivity in order to study mating behaviour. Unfortunately, they weren’t able to draw any conclusions about the male colour schemes. However, research is ongoing so they may figure it out at some point.
And Then There’s the Size
Male stick insects maturing to sport bright colours is fascinating enough. However, there is one more aspect to these two new species that have researchers excited: their size. Apparently, one of the females that researchers observed was 24 cm (9.4 inches) long. That is extremely large for stick insect.
Among the 3000+ known species of stick insects, few species even approach that size. But for some unknown reason, the ones that are big get really big. This may be yet another one of nature’s methods for keeping these particular creatures safe. Maybe their extremely large size makes them off-limits to certain kinds of predators.
At any rate, Madagascar is a place that researchers love because of its incredible biodiversity. They now have two new species of stick insects to study thanks to the discoveries of a group of German researchers. Who knows what they’ll find in the future? Maybe the next species of stick insect they uncover will look more like a lizard than a praying mantis.
Tunis Daily News – http://www.tunisiesoir.com/science/research-in-two-new-species-of-rare-giant-stick-insects-males-turn-livid-blue-or-multicolored-at-sexual-maturity-but-why-14904-2019/