Caterpillars that eat alder leaves

Asked August 3, 2019, 11:48 AM EDT

Hello, we stayed up at the Susitna landing campground last week and there were a lot of caterpillars there eating the alder. Firestone time I’ve seen that around here. Are they an invasive species?

Matanuska-Susitna Borough Alaska pest identification

3 Responses

There are native caterpillars that feed on alder leaves. "Caterpillar" is a broad term that refers to an insect larva that will metamorphose into a butterfly or moth. There are other types of insects, some which in the larval stage of their life cycle resemble caterpillars, that feed on alder as well. Many are native to southcentral Alaska, and some are not.

In order to identify the insect you observed, I would need to see a picture, which can be sent through this form, or you could email it to me directly. If you don't have a picture, a detailed description (including size, shape, color, feeding damage description, general behavior, etc.) could help to narrow down the range of possibilities.

They were light green, no markings on the body. About 3/4” long or less. Were eating alder leaves so only the veins were left.

It sounds like you were seeing alder sawfly larvae. In the larval stage, they resemble caterpillars. There is a native species in Alaska. Two non-native species are also present. Learn more about about them from this Forest Service publication: https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5430500.pdf