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Caterpillar Nest #876051

Asked July 05, 2024, 6:37 PM EDT

We live in Ann Arbor and found this nest on one of the trees in our yard. Are you able to identify this? We think it may be a colony of spongy moth caterpillars. If so, should we remove them or take any other action?

Washtenaw County Michigan

Expert Response

Hi Annie,

I think those are walnut caterpillars - Latin name isDatana integerrima. Based on the bark, I'm guessing these are on a black walnut tree?  They can feed on hickory too but I've only seen them on walnuts.  They are defoliators - but even walnut growers dont worry much about these insects - the defoliation is rarely serious and rarely occurs more than 1-2 years in a row.  And even then, if the trees are severely defoliated, they will put out a second set of buds and should be OK. 

While I've read about them becoming gregarious and clumping up when they are ready to molt or pupate, I've never actually seen that until your photo.  Kind of creepy but also kind of cool - they must really like hanging out together, eh?  They have lots of natural enemies (larval parasitoids, predators) and you'd think a big blob of larvae like that would be very vulnerable - but maybe not in this case!  It looks like the larvae are large and I would bet they are getting ready to pupate.  You can probably knock them into a bucket with soapy water and let them soak a day or two if you want to kill them.  Squirting them with an insecticide will kill them but would also kill any beneficial parasitoids developing inside the caterpillars.  

Personally, I'd let them be - they are native, they've likely finished or nearly finished their feeding for the year and they are just pretty cool little leaf feeders.  I found a good bulletin about this species from NC state - link is below.  Note that we should only have 1 generation here - vs 2 generations in NC.  

Walnut Caterpillar | NC State Extension Publications (ncsu.edu)

Deb

An Ask Extension Expert Replied July 08, 2024, 12:46 PM EDT

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