Caterpillars eating leaves of tree

Question: Any idea what these little caterpillars eating the leaves of our tree are? We hadn't noticed anything until getting home today and the whole tree has lacy, eaten leaves with little black caterpillars and dots (I assume eggs). No webs that I see to indicate the tent caterpillar I'm seeing on Google.

responder: An Ask Extension Expert Replied July 06, 2023, 12:06 PM EDT
response: Thank you for your question, Christy.  Since insects are specific about the species of tree they consume, we first need to identify the tree.  It would appear to be an alder, but there is no photo of the bark on the tree's trunk.  Is this what you understand it to be?  Thanks!

responder: The Question Asker Replied July 06, 2023, 12:11 PM EDT
response: Yes, it is an Alder tree. Thanks for responding!ChristyOn Thu, Jul 6, 2023 at 9:06 AM Ask Extension <<personal data hidden>> wrote:

responder: An Ask Extension Expert Replied July 06, 2023, 12:48 PM EDT
response: There are several pests which feed on alder leaves.  If the caterpillars are about .25 inches in length, this is probably the flea beetle.  https://pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/altica-alnus-flea-beetle#:~:text=Larvae%20are%20black%20and%20about,trees%2C%20but%20only%20rarely%20do and https://agsci.oregonstate.edu/nurspest/insects/alder-flea-beetle Finding an adult to photograph would be helpful.  They should be morphing into adults in August.   Although their "work" is unsightly, they will rarely harm the tree over the long term.  You can read about control strategies here (most of which apply to all beetle pests):  https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5186816.pdf Good luck!

responder: The Question Asker Replied July 06, 2023, 1:36 PM EDT
response: That looks exactly right. Thank you! I’ll look into strategies. On Thu, Jul 6, 2023 at 9:48 AM Ask Extension <<personal data hidden>> wrote:

responder: An Ask Extension Expert Replied July 06, 2023, 6:33 PM EDT
response: Good!

responder: The Question Asker Replied July 06, 2023, 6:42 PM EDT
response: Last question! I see online that pest control is usually not needed, and maybe just fertilizer for the plant for support.  This alder is taller than our 2 story roof and every single leaf I can see is lacy.  Do you think further steps are needed to save the tree or stop the infestation?  I don't want to use pesticides if unnecessary.  Thank you so much for your help. On Thu, Jul 6, 2023 at 3:33 PM Ask Extension <<personal data hidden>> wrote:

responder: An Ask Extension Expert Replied July 06, 2023, 6:54 PM EDT
response: While providing water and fertilizer (in early spring) will help keep the tree healthy, cleaning up fallen leaves in the fall will be far more effective, by removing next year's pests.  Although I can find no specific references to its use, application of a tape around the tree trunk (Tanglefoot) in the spring might stop the movement of insects up to lay eggs which become larvae.   You might also try some of the flea beetle control techniques in this article:  https://extension.umn.edu/yard-and-garden-insects/flea-beetles#chemical-controls-3089563

responder: The Question Asker Replied July 06, 2023, 7:03 PM EDT
response: Thank you so much for the info. So helpful! On Thu, Jul 6, 2023 at 3:54 PM Ask Extension <<personal data hidden>> wrote:

responder: An Ask Extension Expert Replied July 06, 2023, 7:12 PM EDT
response: My pleasure!