Stick insects: Three females remain

Australian biologists have discovered live specimens of a dramatic insect species given up as extinct decades ago.

Big, flightless stick insects. Carlile

A special expedition in February sponsored by the New South Wales National Parks and Wildlife Service located three female Dryococelus australis on a ledge of a small, rocky island called Balls Pyramid off the eastern coast of Australia. “We couldn’t jump for joy or we’d have fallen off the ledge,” says codiscoverer Nicholas Carlile.

Stick insects, or phasmids, look like twigs that have learned to walk. D. australis intrigued naturalists because it was big–the length of a human hand–but didn’t fly. Most insects big enough to be a good snack for predators can fly away, but this phasmid had evolved on islands without such predators.

Early in the past century, people found the phasmids on Lord Howe Island, near Balls Pyramid. Then rats arrived, and the phasmids vanished. During the 1960s, two dead females turned up on Balls Pyramid, but Carlile says he joined the latest expedition without much hope of finding more.

Phasmids hide by day, so the researchers scoured crags and ledges for eggs and any droppings large enough to have come from big insects. One bush had promising droppings underneath. When Carlile and a colleague climbed to the ledge at night, they noticed some crickets that seemed like a plausible source. Just as Carlile was reconciling himself to failure, the climbers saw the live female phasmids.

Early records show that D. australis males did exist, but Carlile speculates that the species can survive without them. In related phasmids, unfertilized eggs eventually develop anyway, into daughters. Carlile says, “It’s possible we’re dealing with an all-female species now.”

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.