Pity the Poor Caterpillar

Pity the poor caterpillar. Here you are, minding your own business, and this tachinid fly comes along and lays eggs in your head.

Good day for the tachinid fly. Bad day for the caterpillar.

The tachinid fly, from the family Tachinidae, is frequently seen buzzing around flowers, like this one (below) in the Storer Gardens at the UC Davis Arboretum. The adults feed on nectar.

"They're parasites," said Lynn Kimsey, chair of the Department of Entomology and director of the Bohart Museum of Entomology. "They often parasitize Lepidoptera caterpillars by laying eggs in them."

They also lay their minute eggs on plants, which caterpillars ingest. The eggs hatch inside the caterpillar, killing it.

"Inside the victims, the larvae breathe free air by perforating the body wall of the host or by a connection to its tracheal system," write Jerry Powell and Charles Hogue in their book, California Insects.

It is not a pretty sight. But then again, tachinid flies aren't pretty--unless you're another tachinid fly.