Chemical Defense

Anisomorpha buprestoides is most commonly known for its unique chemical defensive spray that it produces to ward off predators.  This irritating and odiferous substance is a milky-white, acidic chemical that is secreted as a defensive response from its prothoracic glands (Conle et al. 2009).  Its main components include varying combinations of three different diastereomers: anisomorphal, dolichodial, and peruphasmal (Dossey 2008). The fluid is created and held in long compartments inside the thorax (Eisner 1965), while it is released from notches just behind the head at an anterolateral angle (Littig 1942).  Even in its nymph stage, A. buprestoides’ glands are fully functional and can successfully repel an ant attack (Sondheimer 1970).  A pair of striped walking sticks equipped with their unique chemical defense. Photo used courtesy of Crystal Ernst.

When sprayed, the substance is extremely foul smelling and can cause intense but only temporary irritation in its victim’s eyes and soft tissues (Sondheimer 1970).  In some cases, short-term blindness has been reported (Sondheimer 1970).  The two-striped walking stick will always shoot its venom when triggered by a stimulus resembling a predator (Sondheimer 1970).  The attacker does not have make contact with the walking stick, but merely approach it threateningly to initiate this reaction.  The discharge can be an effective defense against predators such as ants, beetles, birds, and mice (Sondheimer 1970).  That does not mean humans are immune; take caution if approaching one of these bugs.  The two-striped walking stick has sprayed plenty of humans that came too close.  Keep your pets safe too, because dogs have been a frequent victim of these attacks as well.  In fact, A. buprestoides can accurately hit an attacker's eyes within a 30 to 40 centimeter range (Eisner 1965; Sondheimer 1970).  Then, once the compartments of the chemical substance has been depleted, it can take one to two weeks to completely restock the fluid (Eisner 1965). A male two-striped walking stick carries less spray than a female. Photo used courtesy of 

Just as in many other aspects of the two-striped walking stick's behavior, the three different color forms exhibit signficant differences with their chemical defense too.  The white, orange, and brown forms live in varying habitats and thus eat different forms of fauna, which affects the chemical compositions of their secretion (Conle et al. 2009).  Therefore, we see different combinations of the three diastereomers present among the color forms. In addition, the composition also depends on their developmental stage; nymphs generally produce a different combination of diastereomers than the mature adult does (Dossey 2008).   Furthermore, the three color forms behave differently when threatened by an animal.  After they release their chemical defense spray, the brown form of A. buprestoides will stay still until the threat is gone, while the white and orange forms will walk away quickly or drop to the ground if perched on a plant (Conle et al. 2009). 

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