In Defense of Caterpillars

A swallowtail caterpillar everting its osmeterium.

Here’s an immature form of the swallowtails we saw in the last post.  Late instar swallowtail caterpillars like the one above have aposematic coloring, warning of the toxic chemicals they have gradually sequestered from the plants they eat.  Swallowtail caterpillars also have another unique defense mechanism–an organ called the osmeterium, located in the head.  When threatened, caterpillars evert the osmeterium, which resembles two brightly colored fleshy ‘horns’ on the caterpillar’s head.  The osmeterium emits foul-smelling terpenes which, along with the startling appearance and the caterpillar’s thrashing movements, helps to ward off predators.

Swallowtails

Pipevine swallowtail feeding at flowers at Presidio la Bahia

Just got back from the ESA conference in San Diego!  It was fun.

Here’s some pictures I took last spring at the gorgeous flower field outside La Bahia (Goliad, Texas).  Two common varieties of Texas swallowtail butterflies, family Papilionidae, feeding in the flowers.  Swallowtails take their name from the long ‘tails’  common on the wings of butterfly species in this family.  Butterflies feed through siphoning mouthparts in the form of a long, coiled tube, called a proboscis.  As lepidopterans metamorphose from caterpillars to butterflies their mouthparts change drastically from leaf-chewing mandibles to a nectar-sipping tube.  This change is mirrored in their digestive tracts, which in caterpillars take the form of a fairly simple tube, and in butterflies becomes much more complex.

Giant swallowtail in the flowers at La Bahia, Texas.