Stick insects are very good at camouflage. It's sort of in their job description to hide from predators, so entomologists are puzzled by two new species where the adult males do the exact opposite, standing out as much as possible. The explanation for this behavior might be a life lesson for us all.
Stick insects' hiding skills have seen them thrive in many parts of the world, but the biodiversity hotspot of Madagascar has produced some particularly impressive individuals, such as Achrioptera maroloko, whose females grow to 24 centimeters (10 inches).
While leading the first team to scientifically describe A. maroloko, and another species A. manga, Dr Sven Bradler of the University of Göttingen was struck by the bright colors. “Nearly all of the 3000+ known species of stick insects try to be inconspicuous and just look like twigs,” Bradler said in a statement. “There are a very few, very large exceptions – and we have just discovered a couple more of them.”
The adult males Bradler described are colored to stand out, not blend in. Maroloko has bright blue spots on a black body, while manga is bright all over. Both are hard to miss among forest greens and browns.
There is little doubt the colors are a form of sexual signaling. In captivity, the timing of the males' first mating attempts matches the arrival of their new colors. Younger males, like the females, look twig-like. Presumably, the females have a taste for blue, but Bradler, and Dr Frank Glaw of the Bavarian State Collection of Zoology, with whom Bradler wrote the paper in Frontiers in Ecology and Evolution on the species, didn't think that was enough. In the wild, something so visible is likely to be seen by one of the abundant ravenous predators before he can catch a mate's eye.
So here's where the life lesson on comes in. Bradler and Glaw think the males have turned lemons to lemonade. “Males searching for a mate have to move about more, so pretending to be a stick becomes tricky. Better perhaps to plump for the opposite: a brightly colored warning,” Glaw said.
It's common enough for creatures to use distinctive colors that tell the world they taste bad, and the authors think the stick insects may not be lying. These males have particularly well-developed neck-glands that produce unpleasant substances. By evolving extra repellant and bright colors together, the males may have made themselves less vulnerable to predators and more likely to get laid at the same time.
Unfortunately, these stick insects face a danger evolution did not prepare them for – their habitat is very threatened by logging, and without sticks, there are no stick insects.