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How Predators Avoid Getting Eaten by Herbivores

By Ross Pomeroy

It's a bright summer day, and a predatory coccinellid beetle is lazily resting on the leaf of an alfalfa plant, its stomach brimming after a veritable feast of tiny aphids. Suddenly the ground quakes, a result of cloven hooves impacting the ground. A dark shadow blocks out the sun, shading the beetle and the plant. The shadow's owner is a humongous beast: a black and white splotched Holstein cow. As its mouth dips closer and closer to the alfalfa, watering in masticatory anticipation, the beetle feels the bovine's hot, humid breath. If the beetle doesn't act quickly, it will become an appetizer for an herbivore!

Luckily for the beetle, it has a mechanism for dealing with such an occasion. As just discovered by researchers at the University of Haifa in Israel, in order to avoid incidental ingestion by mammalian herbivores, coccinellids quickly release their hold on plants and roll off to fall down to the ground below.

According to the researchers, the action is initiated when the beetles feel the mammal's breath. In the lab, the researchers lightly blew beetles resting on a plant with air that had different qualities. One air treatment was heated to 96.8 degrees F (mimicking the temperature of breath); one treatment was at 80-90% relative humidity (again, mimicking breath); one used both heat and humidity; and in the final treatment, one of the researchers simply breathed on the beetles from an intimate distance (without accidentally swallowing them).

As indicated in the table, breathing on three different beetle species caused them to drop off the plant between 80 and 90 percent of the time. In another experiment, beetle larvae reacted in a similar fashion.

"The fact that coccinellids have adapted to sensing mammalian breath and evolved a behavioral mechanism for avoiding incidental ingestion points to the centrality of the direct threat that grazing mammalian herbivores impose on these beetles," the researchers say.

It appears that this is one example where predators have evolved a mechanism to avoid -- ironically -- being eaten by herbivores.

Source: Ben-Ari M, Inbar M (2013) When Herbivores Eat Predators: Predatory Insects Effectively Avoid Incidental Ingestion by Mammalian Herbivores. PLoS ONE 8(2): e56748. doi:10.1371/journal.pone.0056748

Steven Ross Pomeroy is the assistant editor for Real Clear Science. Follow him on Twitter @SteRoPo.

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