What's That Bug? does not endorse extermination

Subject: Caterpillars
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

Sawfly Larvae or Caterpillars???

Speckled Green Fruitworm

Dear Kelly,
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?

Sawfly Larvae or Caterpillars???

Speckled Green Fruitworm

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.

What's That Bug? does not endorse extermination
Location: Anvik, Alaska

4 Responses to Speckled Green Fruitworm on Willow in Alaska

  1. Gddubois says:

    I work with forest insects and that caterpillar has become a focus of much of my time the past 2 summers, it’s a Lepidopteran. It’s a moth larvae from the family Noctuidae. The species is probably Sunira verberata. It’s been doing a lot of defoliating along the east and west sides of the Alaska range, in the wood tic-chiks around Holy Cross and up by Anvik. They have been pretty active for the past 3 years and numbers have been increasing. They don’t become adult moths until the fall. The moths you saw earlier this year were a different species , the name slipped my mind.

    • bugman says:

      Thanks so much for providing your comment. We are changing the category, but BugGuide has no images of the Battered Sallow, Sunira verberata, Caterpillars. This is a native species. Do you have any information on why populations are growing or why they have suddenly become a concern?

      • Gddubois says:

        Sorry for the long delay in the followup. After some rearing and DNA analysis, our samples have been confirmed as the native Orthosi hibisci, The speckled green fruitworm. We have confirmed samples from Bethel and areas around Lake Clark, Telaquana Lake and Chakachamna Lake. We also had numerous images of damage and larvae sent to us from the Anvik area as well as a number of other areas in Western Alaska. It’s likely but not I cannot say 100% that it’s Orthosia hibisci doing the damage.

        We don’t know why populations have been growing in the last few years, that is hard to say. We have seen the damage in a number of inaccessible areas that we get to by float plane and I imagine that it has become a concern because there is also significant amounts of visible damage and large caterpillar and moth populations in areas where there are people.

        There is quite a bit of information out there on this critter as its range is transcontinental, it has a very wide host range and has been a fruit orchard pest for some time.

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