Stick insects travel long distances—by being eaten by birds

Stick insects can’t travel long distances by themselves, but they’ve somehow managed to spread far and wide, even dispersing across unconnected islands. Now, scientists have discovered one way they may have achieved this: being eaten by birds.

Many plants use birds to disperse their seeds. Birds eat the fruits, move away from the plant, and then poop, depositing the plant’s seeds in a new location. When insects are eaten it is assumed that they and their unborn young don’t survive, but a team of researchers wondered whether a similar mechanism helps insects transport their offspring long distances. Stick insects make eggs that have a very hard shell, which can survive acidic environments, such as those in bird guts.

The team fed eggs from three species of stick insect to brown-eared bulbuls (Hypsipetes amaurotis, pictured), a medium-size bird that is common in eastern Asia and one of the main avian predators of stick insects in Japan. A few hours later the birds passed the eggs, and the researchers found that for each species, between 5% and 20% of the eggs had survived unharmed. A couple of eggs from one species, Ramulus irregulariterdentatus, even hatched, the team reports today in Ecology .

If the strategy is one the insects have used in the past, there should be a correlation between the genetics of various stick insect species and bird flight paths. That’s something the team plans to investigate next.