Caterpillar larva on Apple leaves
These look like an infestation of yellownecked caterpillars. They tend to aggregate in large crowds when young. They eat the foliage of many shade trees and also fruit trees. On large trees, this is not a big issue, but on small or young trees, the damage of most or total leaf loss can impact the tree severely.
Happily, because yours is a small tree, the easiest thing is to manually remove them. Put on gardening gloves and scrape them into a container of soapy water, which will kill them. There is only one generation a year, so that should do it for this year. Keep an eye out next year.
The adult is a moth which is attracted to light at night. Avoid leaving on night lights as they attract a slew of unwanted insect pests.
Are yellownecked caterpillars good or bad? They are bad if they kill your tree. This is a native insect that no doubt supplies a food source for birds, but in your circumstance, you'll want to get rid of them.
Well, I looked up the yellow neck and it is possible. I agree with everything except the color of these catepillars (larva). It said the young ones were black and as they matured become cinnamon colored. Mine are cinnamon colored from the start. But boy do they eat! And fast. I am glad I noticed them or I would have no apple tree!
yellow neck or not, they are certainly a pest. I think I'll feed to my chickens.
They will make great chicken food for sure! Good luck and don't hesitate to contact us again if you have additional questions.