Monday, September 21, 2009

Organic Chemistry and a Walkingstick Insect

The “two-striped” walkingstick (Anisomorpha buprestoides) is a familiar species in the southeastern United States. Here in Florida, there are a few varieties, each of which can be distinguished in field by the color of the parallel stripes that run down the length of their back. For example, the male and female pictured below (snapshots taken last week) are commonly referred to as the “brown two-striped” walkingstick. Other colormorphs include the “white two-striped” and the “orange two-striped”.

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!


  1. Interesting article and nice pics. I have seen Walkingsticks on occasion, but they always seem exotic to me - maybe I just don't know where to look. Thanks for the link!

  2. Hi
    I saw one this week in North Florida, very similar to the bron two stripped but was not black on the flanks/ you know anythiing aabout that? By the way, what did you study (just curious)? merci, Annie

  3. I have seen the two striped in Thonotosassa, FL. I was scared of them because I never knew what they were, lol. They looked like some alien bug to me. Thank you for this informative article about them, I am now fascinated to know more.

  4. I just found a batch of them under some barn tin in Texas! I thought the males were their babies lol