With more than 3,000 species spread across the world, the mostly immobile slow-moving stick insect has puzzled scientists with just how it's been able to establish itself on every continent in the world, with the exception of Antarctica. Japanese researchers now believe they have the answer.
Disclaimer: If you’re eating at the moment then you might want to put your food down.
Stick insects employ a Trojan Horse method of sorts when birds eat females with viable eggs contained within their bodies. These eggs can then pass through the birds undigested, allowing the bugs to expand their habitat without having to travel long distances themselves. All conditions needed to achieve this mode of travel are met by the bugs: female stick insects are able to produce viable hard-shelled eggs without fertilization. After hatching, their offspring forage for food and are able to survive on their own.
It’s the same technique employed by plants who cannot move around themselves.
“If insect eggs can pass through birds unharmed, we could say that insects, just like plants, are using birds as a means of long-distance transport,” said the researchers in a statement.
To test their theory out, they fed eggs from three different species of stick insects (Phasmatodea) to their main predator, the brown-eared bulbul (Hypsipetes amaurotis). In all three species, between 5 and 20 percent of eggs pooped out were unscathed. The findings are published online in Ecology.
While plants employ eye-catching, nutritious fruit to get animals to eat them, stick insects are plain and hard to see. This consumption strategy could help the bugs expand their habitat, diversifying their dispersal around the world. The invertebrate herbivores live up to three years in the wild, reaching lengths of just barely half an inch up to more than a foot long. They spend their days mostly motionless, hiding under plants in grasslands and forests.
"Our next step is analyzing the genetic structure of stick insects" said Professor Suetsugu. "Based on this, we'd like to investigate whether similar genetic structure of stick insects can be found along birds' migration flight paths, and whether there are genetic similarities between stick insects and plants that rely on birds for seed distribution".
The team says their investigations will help to reveal how the dispersal of stick insect eggs by birds could affect the distribution and gene flow of stick insects.