While a number of techniques exist for finding caterpillars, we have found the following three best suit our needs.

1. UV Flashlights

Our main method is to go out after sunset, ultraviolet (UV) flashlights in hand, in search of caterpillars that fluoresce. Many caterpillar species fluoresce when UV light is shined on them and this fluorescence is much easier to see in the dark.

Tobacco Hornworm with camera flash. Photo by Sourav Ghosh.

Tobacco Hornworm fluorescing under UV light. Photo by Sourav Ghosh.

2. Visual Searches

On occasion, we do daytime sessions to search for caterpillars that feed on or within leaves (the latter are called leafminers) or other plant parts, or that manipulate leaves in various ways to create shelters (leaf rollers/folders/tiers). On rare occasion, we have found caterpillars that feed on substrates such as fungi.

Leafmines

Leafmine of Coptodisca splendoriferella (no common name). The hole on the bottom left is created by the larva, which sews the two surfaces of the cut-out section together with silk before dropping into the leaf litter to pupate.

Leafmine of Coptodisca splendoriferella with backlighting. Here you can see the structure of the “mine” created by the larva, as well as its frass.

Leaf constructions

Leaf construction of Oak Leaftier Moth. The leaves are tied together with silk, to shelter the larvae while they feed from the inside of the construction. The brown sections of the leaves are where the caterpillar has eaten the inner layer of the leaf tissue.

Larva of Oak Leaftier Moth that was residing in the above construction. Notice the leaf tissue missing between the veins of the leaf.

3. Beating Sheet

From time to time we sample vegetation using a beating sheet, either during the daytime or after sunset.