Chemical and Physical Fecal Defense Mechanisms in Insects
Biology 342 Fall 08
Chemical and physical use of feces in insect defense mechanisms
Use of feces in defense has been observed in a variety of insect species. Feces can have a role as a physical barrier, chemical deterrent, or as a combination. The chemical composition of feces is directly related to the insect's food sources, making it an interesting way to study the role of the environment in the defense mechanisms of an insect species. The examples of frass chains and fecal shields show the physical and chemical roles of feces in defensive behaviors. By choosing these specific behaviors, we are not attempting to encompass the full diversity of uses of feces in defensive behaviors, but rather we hope to demonstrate two primary classes (physical defense and chemical defense) in which feces can be used.
Fig 1. Eunica bechina larvae on frass chain (Photo by Freitas and Oliveira 1992).
Frass chains in nymphalid butterfly larvae are an example of the use of feces as a physical barrier. These stick like structures are constructed from feces and silk. They are attached to a leaf and provide a resting place for larvae when not feeding. This provides a defense against predators that walk along leaves in search of prey.
Fig. 2 Plagiometriona clavata larva with fecal shield. Copyright © 2005 Tam Stuart.
Chrysomelidae beetle larvae save feces in a "fecal shield" suspended above their backs. These shields contain chemicals obtained from a plant the larvae preferentially feeds on. These chemicals are a deterrent to many predator species. Although they are termed "shields," this is primarily a chemical, rather than physical, defense.