Location: Anvik, Alaska
June 24, 2016 3:32 am
Hello im from Alaska and we just noticed all these caterpillars everything eating up all the leaves off of willows and trees.. It’s very on common for these to be around here. There trillions of them everything I mean every where. Please let us know if u know what they are. This spring there were millions of Moths flying around that was very weird and wasn’t common at all.
Signature: Kelly Kruger
Alas, there is not enough detail in your images to tell for certain if these are Caterpillars, or as we suspect, Sawfly Larvae. According to Insects.About.com: “Caterpillars are the larvae of butterflies and moths, which belong to the order Lepidoptera. Sawfly larvae look similar to caterpillars, but are an entirely different kind of insect. Sawflies are related to bees and wasps, and belong to the order Hymenoptera. Like caterpillars, sawfly larvae usually feed on plant foliage. How can you tell the difference between a sawfly larva and a caterpillar? Count the prolegs. Caterpillars may have up to five pairs of abdominal prolegs (see parts of a caterpillar diagram), but never have more than five pairs. Sawfly larvae will have six or more pairs of abdominal prolegs*. Another notable difference, though it requires a closer look, is that caterpillars have tiny hooks called crochets, on the ends of their prolegs. Sawflies don’t. Another, less obvious difference between caterpillars and sawfly larvae is the number of eyes. Caterpillars almost always have 12 stemmata, 6 on each side of the head. Sawfly larvae usually have just a single pair of stemmata.” In two of your images, the camera is entirely too far away to see individual detail in these larvae. In the one close-up image, the largest larva is partially out of focus, and the only other larva that can be viewed clearly is half cut off at the top of the frame. We wish we could count the prolegs, though it really seems to us that there appears to be six pairs, which would make these Sawfly Larvae and not Caterpillars, but again, the image is too blurry at that critical part of the anatomy that we cannot be certain. Additionally, we can find no images online of either Caterpillars or Sawfly Larvae that have this particular coloration and markings. The jury is still out on your identification request. Can you return to the willows and get a higher resolution, sharper image? or can you count the prolegs and get back to us?
Update: December 3, 2016
Thanks to a new comment, we now know, thanks to DNA analysis, that this is a Speckled Green Fruitworm, Orthosia hibisci, a species of Cutworm that is profiled on BugGuide where hosts plants are listed as: “decidious trees and shrubs including: apple, crabapple, cherries, plums, poplar, maple, willow and white birch.” It seems to us that this would be a species eagerly eaten by insectivorous birds, and we can’t help but wonder if bird populations in the area are compromised.