Representing one species of the more than 2500 known walkingsticks, Anisomorpha buprestoides are notorious for their ability to produce and dispense noxious and irritating chemicals. Used as a defensive mechanism, the harsh organic isomers (different compounds with the same molecular formula; i.e. they’re bonded differently) produced by the walkingstick are sprayed from the thorax into the face of would be predators - and the occasional annoying human.
Recent work published to the Journal of Chemical Ecology has shown that the isomers produced by A. buprestoides can be found as one of three diastereomers: anisomorphal, dolichodial, and peruphasmal. Furthermore, the relative proportions of the stereoisomers produced are unique to the age and geographic location of the walkingstick.
NOTE: To avoid painful besiegement by “chem-talk,” linked here is a quick refresher video on isomers; for those long removed from an organic chemistry class (Courtesy of YouTube’s “ValChemistry”).
The correlation that has been found to exist between the insect’s chemical defenses and its location and maturity seem to suggest a genetic based mechanism of development as opposed to a plant (food) or environmental based means of acquisition.
Incidentally, the photographing of a male and female together is by no means a rare occurrence. The male of the species typically attaches himself to the female when she reaches sexual maturity. He does this by locking his cerci (claspers located at the end of his abdomen) to her abdomen. There he remains – indefinitely. He’ll remain attached through her repeated molting cycles, frequently even observed being dragged behind her as dead weight…
Dossey, A., Walse, S., & Edison, A. (2008). Developmental and Geographical Variation in the Chemical Defense of the Walkingstick Insect Anisomorpha buprestoides Journal of Chemical Ecology, 34 (5), 584-590 DOI: 10.1007/s10886-008-9457-8
UPDATE: Steve (a chemist) has posted an addendum to this article at Bridgehead Carbons with additional info on walkingsticks and the chemistry described in the cited article. Check it out!