Georgetown College. Georgetown University.

“Defecation ecology (‘faecology’) is another area that I’m working in,” says Dr. Martha Weiss, who has recently written a lengthy article on insect defecation behavior and ecology, published in last year’s Annual Review of Entomology.

In their laboratory, Weiss and her students have also been observing the intriguing shelter-building behaviors of caterpillars (larvae of the silver-spotted skipper) who build shelters on leaves for the duration of their larval (or caterpillar) phase, and leave their shelters only for brief periods during which they either feed or build themselves a new, larger shelter to accommodate their growth. Weiss and her students have been investigating the process through which these caterpillars are able to build shelters that are consistent in shape and proportion.

They are also studying the interaction between these caterpillars and predatory wasps (paper wasps), discovering sight-smell associations are learning mechanisms for the wasps. Weiss’ lab has found that wasps do not associate the presence of a shelter with the caterpillar that resides in it until the wasp has had the experience of killing and tasting a caterpillar in the presence of their shelter. Their research indicates that the smell released by the leaf as a result of the shelter’s presence becomes associated in the wasp’s mind with the taste of the caterpillar. After this association is made, wasps are then motivated to invade shelters and to prey on the caterpillars.

During their observations, Weiss and her students noticed that the caterpillars would project their frass (excrement) impressive distances away from their shelters and would not tolerate the presence of frass in the shelters, reacting by throwing or pushing it out if Weiss or her students would carefully place a piece of frass inside a caterpillar shelter. After testing out a number of hypotheses, including that the frass posed a health hazard or simply filled up valuable space, Weiss and her students learned that the smell of the frass was actually very attractive to their predatory wasps, and that this was the reason for the caterpillars’ peculiar “housekeeping” behavior. Importantly, these results may contribute to the development of biological controls (a method of controlling agricultural pests using predatory or parasitic insects, rather than harmful chemicals) for insect pests.

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