To escape late autumn’s chill, Bug of the Week heads to Ocala National Forest in Florida where it’s hot, hot, hot during mating season of the twostriped walkingstick. These giants of the insect world are among the largest insects in the continental United States. One gorgeous female I captured was almost four inches long. Twostriped walkingsticks enjoy a vegan lifestyle dining on leaves of crepe myrtle, roses, oaks, rosemary and, likely, several other trees and shrubs. While the details of the life of this curious insect are not fully known, autumn is the season when mating pairs are most abundant.
Male vs. Female walkingsticks
Walkingsticks discharge noxious secretions from this opening.
In addition to their notable markings, one striking feature of these beauties is a curious discrepancy between the size of the females and the size of their mates. In the world of mammals and birds, the general rule is that males of the species are larger than the gals. However, in the realm of insects and spiders, when it comes to size, females are sometimes larger. Does size really matter and, if so, what forces shape large females and smaller males? Several explanations have been proposed to help explain these size differences in insects and their kin. For many insects, there is often a direct and increasing relationship between the size of the body and the number of eggs a female can produce. Big mammas simply leave behind more offspring than small ones and thereby gain an advantage in the evolutionary game. This may be accomplished by molting an extra time relative to the male and spending slightly more time growing and becoming larger than their puny mates. The male walking stick has a slightly different situation on his many hands. His contribution to the mating game is rather small, just a deposit of tiny sperm to fertilize the female’s eggs. Rather than battle other males for a chance to mate, being at the right place at the right time may play an important role in the walkingstick’s mating game. By developing rapidly a male walkingstick may gain an evolutionary advantage by being the first of his cohort to reach maturity, find a mate, and win her affections before other suitors arrive at the scene. However, rapid development may come at the expense of body size. All things equal, a small walkingstick may reach maturity quicker than a large one and thereby win the dating game. How does an insect so large go unnoticed by scads of hungry predators that might like to make it a tasty meal? Like many other bugs we have visited such as Eleodes beetles and Nasutitermes termites, twostriped walkingsticks pack a potent chemical wallop. Just behind the creature’s head are small openings. When under attack the walkingstick can discharge a highly irritating secretion from these ports. One unfortunate human who was apparently eyeballing the walkingstick received a rather nasty surprise. A quote from a scholarly account of this incident was “The pain in his left eye was immediately excruciating; being reported to be as severe as if it had been caused by molten lead.” Although I suffered no misfortune by these beautiful creatures, caution should be observed and please don’t look them in the eye.
References:
Special thanks to brave Paula for spotting and capturing walking sticks used in this Bug of the Week. Resources used for this episode include: Behavioral causes and consequences of sexual size dimorphism by Wolf U. Blanckenhorn, Achieving high sexual size dimorphism in insects: females add instars by Toomas Esperk, Toomas Tammaru, Soren Nylin, and Tiit Teder, and Defensive spray of a phasmid insect by Thomas Eisner. To learn more about twostriped walking sticks please visit the following web site.