Caterpillar Use of Frass
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Unusual Use for Fecal Pellets by Butterfly Caterpillars? |
Caterpillars of several species of butterflies attach frass (excrement, fecal pellets) to the midrib of the leaf they are eating. Hatchling caterpillars add these pellets to the tip of the leaf or, depending on species, from the side of the leaf.
 Red-Spotted Purple butterfly |
 Red-Spotted Purple butterfly fecal pellets on a leaf vein |
 Microscope view frass - excrement on a leaf vein |
Caterpillars will actually extend a leaf vein with frass or create a line of frass from the side of a leaf.
 Viceroy butterfly |
 Viceroy butterfly caterpillar on an extended leaf vein |
 Poor quality photo of Viceroy caterpillar on extended leaf vein |
Ruddy Daggerwing butterflies lay eggs on other parts of the leaf than Viceroys. As a result, the caterpillar starts eating where-ever it hatches and creates a line of frass off the side of the leaf.
 Ruddy Daggerwing butterfly |
 Ruddy Daggerwing caterpillar resting on a line of frass |
 Badly out of focus photo of Ruddy caterpillar on a fecal leaf extension |
Other species of butterfly caterpillars will also create leaf extensions with their frass. The Florida Purplewing and Goatweed Leafwing are two other species that exhibit the same habit.
Although it is theorized that this behavior is to discourage predators, some caterpillars exhibit the opposite action. Several are noted for thier 'frass-flinging' custom. These caterpillars create nests of leaves and literally pick up and fling their frass out of their nest of leaves. It is theorized that by doing so, predators will find it more difficult to locate the caterpillar. Some lepidoptera caterpillars attach frass and leaf bits to their bodies. Others will create a nest of frass and pupate inside the frass nest.
Although it is theorized that this behavior is to discourage predators, some caterpillars exhibit the opposite action. Several are noted for thier 'frass-flinging' custom. These caterpillars create nests of leaves and literally pick up and fling their frass out of their nest of leaves. It is theorized that by doing so, predators will find it more difficult to locate the caterpillar. Some lepidoptera caterpillars attach frass and leaf bits to their bodies. Others will create a nest of frass and pupate inside the frass nest.