Name that Caterpillar
Hello Cooperative Extension Expert, Please identify for me the caterpillar in the attached photo. My neighbor has a deck under an oak tree and these caterpillars are falling out of the tree as well as raining down their frass on her deck, which she recently had powerwashed. The oak tree is a very tall one. She has never had this problem before and I have never seen such an intense and extensive caterpillar problem as this in this area in Maryland, northeast of Washington, DC. Spraying a tree of this size would be costly as would be pruning it because the limbs are high up. Is there any other remedy? Can the stains be safely washed from her deck without resorting to powerwashing it again? Thank you for your help with this problem. Please
The caterpillar in your photo is called a Yellow-necked Caterpillar.
You can compare to here:
This has been a big year for caterpillars, which also makes it a banner year for butterflies, songbirds and other insects and wildlife that eat them. Unfortunately it also makes for a lot of droppings on underlying patios, driveways and decks.
When dry, your neighbor should be able to simply sweep them off, or even just hose them off if they are wet. They aren't usually sticky or problematic, though she may need to do it multiple times.
It is important to know that the caterpillars as well as the trees are native and have evolved together for eons, along with the other flora and fauna. Every few years we will have a bumper crop of them that makes them noticeable to homeowners but is natural and actually a good sign of an ecosystem working well. It won't likely happen in large numbers again for a while.
Thank you for the quick response, Christine. Could you also let me know if this is a beneficial or harmful caterpillar (or neutral) and if a mild detergent or soda water would be sufficient to clean the stains off my neighbor's deck?
The last paragraph of my answer above perhaps should have been more clear.
The fact that these are native caterpillars and native trees means that they are beneficial and an integral part of the web of life in nature and have been since before we were here.
We don't have any info or research on cleaning.