Transcript:

ambience: dawn at desert

This time of year, heavy monsoon rains saturate the dry soil of Arizona’s Sonoran Desert. The acacia shrubs are in bloom, and their nectar attracts colonies of ants to nest at their base. The acacia flowers also attract butterflies, and the ants and butterflies have evolved a remarkable interdependent relationship. I'm Jim Metzner, and this is the Pulse of the Planet. Diane Wagner is an assistant professor in the Department of Biological Sciences at the University of Nevada.

“After the monsoon rains the butterflies arrive. And the butterfly I’m talking about is the Reichert’s Blue, and this is a small, dime-sized butterfly. And the juvenile stages of the butterfly are tended by ants, the way you might’ve seen ants tending aphids or treehoppers.”

Well, some species of ants are known to tend herds of aphids like cattle, feeding on the aphids’ secretions and in return, protecting them from predators. Well, in the same way, these Sonoran Desert ants tend the caterpillars - the larvae of the Reakirt’s blue butterflies.

“The ant stands on the caterpillar, and it touches it with its antennae, and it touches it in ways that tell the caterpillar to secrete a droplet of food. So the ant can feed from the caterpillar, from a gland on the caterpillar’s back and in return, if a predator approaches the caterpillar, the ant will chase it off. So the ants provide protection to the caterpillars and the caterpillars feed the ants in return.”

This relationship only lasts during the juvenile stage of the caterpillar’s life. Once it’s transformed into a butterfly, it has but a few moments to fly away, otherwise the ants will kill it.

Pulse of the Planet is presented with support provided by the National Science Foundation.

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