No, this Bug of the Week is not about Lesley Hornby, the skinny English super-model. Twiggy refers to a remarkable group of insects that bring a whole new meaning to the phrase “masters of disguise.” Walking sticks are also known as stick insects or leaf insects in various parts of the world. They make their living by eating the leaves of plants. In Appalachian forests, they sometimes become quite abundant and actually defoliate trees. Although lacking the tough armor of beetles and evasive flight of butterflies, they have perfected the art of crypsis, that is, to resemble features of the environment to avoid detection by animals wanting to eat them.
A northern walking stick busts a pose on a tree trunk.
In addition to having greatly elongated body regions and appendages matching the colors and textures of twigs, walking sticks move and pose in ways designed to fool sharp-eyed predators. As walking sticks search for leaves, they sway slowly back and forth mimicking the movement of a branch in the breeze. When not feeding or actively moving about, they assume a branch-like position with the front pair of legs extended directly forward. Their ability to hold an unflinching pose for hours is the envy of every mime. Unlike most adult insects, the northern walking stick never develops wings and the nymphs and adults are quite similar in appearance. Some species of stick insects lay eggs on plants while others simply deposit them on the ground. For our most common stick insect, the northern walking stick, winter is spent in the egg stage. A southern cousin of northern walking stick is the longest insect in the United States and measures about half a foot. Some tropical stick insects exceed 12 inches in length. When camouflage fails to fool a hungry predator, walking sticks may have another trick up their twig. Several species have evolved glands on their thorax that emit foul smelling and irritating chemicals to foil attacks by their enemies.
References:
“An Introduction to the Study of Insects” by Borer, DeLong, and Triplehorn and “Defensive Production of Quinoline by a Phasmid Insect (Oreophoeres peruana)” by Eisner et al. were used as references for this Bug of the Week. We thank Jo Ann, Tamma, and Eileen for sharing their walking sticks and providing the inspiration for this episode. To learn more about the northern walking stick, please visit the following web sites.
http://www.fcps.edu/islandcreekes/ecology/northern_walkingstick.htm
http://bugguide.net/node/view/34736