Excerpts from a fascinating article in The New York Times:
Naturalists recently witnessed several species of milkweed butterfly harassing, subduing and subsequently feeding on milkweed caterpillars, presumably to get their fill of toxic alkaloids inside the larvae.This behavior was described in an article published Wednesday in the journal Ecology. The authors of the paper say they are unaware of similar behavior being documented among other butterflies, or any insects for that matter, that are so closely related. Although butterflies had previously been observed feeding on grasshoppers that harbor toxic alkaloids, no one had ever documented adult butterflies stealing such compounds from their own kin.Scientists did not have a word to describe this toxic behavior, so the study’s authors came up with one: kleptopharmacophagy... [steal-drug-eat]Mr. Soong and Mr. Tea spent hours watching seven different species of milkweed butterfly, including Blanchard’s ghost and the ismare tiger butterfly, scratching caterpillars, both dead and alive, so violently with mighty claws on their feet that the caterpillars’ internal juices oozed out... They also observed butterflies doing the same thing to the leaves of plants known to contain toxic alkaloids...Having a steady supply of pyrrolizidine alkaloids is also important for male milkweed butterflies. These alkaloids are an ingredient in mating pheromones and also in nuptial gifts...“Butterflies have a whole repertoire of really gross and nasty behaviors,” Mr. Tea said. One example is pupal rape, a phenomenon in which male butterflies force their way into the chrysalises of female butterflies that haven’t finished metamorphosing and force them to mate, he said.
All of this is new to me. You learn something every day.