Hi Greg,

Thank you for reaching out to the UVM Extension Master Gardener Program with
your question. I am wondering if you noticed any egg masses on the Larch tree or neighboring trees, especially if there are any Oak trees nearby? I have included a link showing a possibility of what an egg mass might look like - scroll down a bit and look at the third picture on the right. Sometimes they lay on the side of the house. If so, can you share a picture of what yours look like? We are sharing your pictures with an Entomologist to see what they say, but I haven't heard back yet.

https://cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/whats-bugging-you/spongy-moth

I also suggest that you look at the caterpillars again to see if they are growing since it has been 2 days or do you think they are staying small. If the caterpillar is growing, it might be the Spongy Moth caterpillar. I think I've seen that most Caterpillars that like Larches are greenish not black. The first link below talks about the favorite trees that the Spongy Moth caterpiller likes in VT - you can find the list in the second link called Biology. The Larch is listed as a secondary tree that they like.

https://vtinvasives.org/invasive/spongy-moth-formally-gypsy-moth#:~:text=Spongy%20moth%20is%20known%20to,even%20occurs%20in%20white%20pine.

This link is a UVM link talking about the Spongy Moth, in general, in VT. I am not diagnosing that you have Spongy Moth, but you said they were black and on your house. Scroll down and look at the side of the house - you said they were on your porch.

https://www.uvm.edu/extension/spongy-moths#:~:text=The%20caterpillars%20are%20greyish%20with,your%20hair%20or%20plants%20below

Here is a link explaining some precautions you can take, if the caterpillars are indeed the Spongy Moth.

https://fyi.extension.wisc.edu/spongymothinwisconsin/pest-management-2/management-guide-for-homeowners/

I don't know how long it takes to hear from an Entomologist. In the meantime, my suggestion is to look around and observe more: are the caterpillars growing bigger; are they eating the tree; are they on other nearby trees that are on the list; how widespread are they; where might they have come from; do your neighbors have them; notice if birds are eating them; if not and there are a lot of them, can you knock the population down safely and strategically; and as the first article says, don't forget to make sure you water your (Larch) tree if it gets dry. You want to baby it, especially since it is a treasured tree. If you have any questions or concerns, or if anything changes, please email me back. Likewise, I will email you back if I find out anything. Best of luck,

Hello again Greg,

We heard back from Dr. Margaret Skinner, UVM Extension Entomologist, who said, "I can’t identify these based on the images and the fact that they don’t appear to be feeding on the larch tree. Given the number and size of the caterpillars, if larch was a host, there should be evidence of feeding. It appears to be some sort of tussock moth, related to spongy moth, but a different species. The images are a bit confusing. The individual larvae are blackish while the ones that are crawling on the webbing appear yellowish. A few possibilities might include:
White-marked tussock moth, Orgyia leucostigma https://en.wikipedia.org/wiki/Orgyia_leucostigma
Rusty Tussock moth Orgyia antiqua nova https://en.wikipedia.org/wiki/Orgyia_antiqua

Although we may not be able to IDd them to species, the homeowner could either spray them off with a strong stream of water to knock them off the tree and then sweep them up. If they are feeding on the larch, then they could apply Bacillus thuringiensis kurstaki (Btk)."

Dr. Skinner is willing to take a closer look if you would like to send in some caterpillars. If interested, please complete this form and bring the specimens directly to Dr. Skinner at the UVM Entomology Research Lab at 661 Spear Street (Margaret does say there is substantial construction there at this time) or to the UVM Plant Diagnostic Lab / Helpline office at 206 Jeffords Hall, 63 Carrigan Drive.

I hope the information from the entomologist is helpful. Best of luck,