Stick insects lure ants with fatty knobs
Piotr Naskrecki/Minden Pictures/Corbis

Stick insects lure ants with fatty knobs

Stick insects are masters of camouflage, fooling predators, prey, and even rivals into thinking they’re nothing more than harmless twigs. But according to new research published in the Journal of Chemical Ecology, their unborn children may be just as cunning: Their eggs have “knobs” coated in a special kind of fatty acid that also covers the surface of seeds that are irresistible to ants. The ants drag the eggs to their nests, where they remain protected until they hatch several months later. But just how do the knobscalled capitula—attract ants? Previously, researchers knew only that some species of stick insects were dropping eggs on the ground in the same way that some trees dropped their seedsa method of dispersal that relies on ants and other creatures to ferry the seeds to far-flung places. To test what was happening to the stick insect eggs, scientists scattered a batchhalf with capitula, half withoutfrom Goliath stick insects (Eurycnema goliath) around wild nests of green-headed ants (Rhytidoponera metallica). The ants ignored eggs without capitula but collected almost 40% of those covered in the fatty acid knobs. In a further experiment, scientists enticed the ants to retrieve plain plastic balls by gluing capitula on the otherwise inert spheres. The new research suggests that fatty acids may underlie many interactions between plants and insects, and adds to a growing body of evidence that fatty acids are a key signal in plant and animal communication.