Funny you should mention this, I just came in from picking those nasty things off my sqash, zucc, butternut & pumpkin plants. I may be wrong, but they were first in my garden this summer on my cucumbers and someone told me they were pickle worms or squash borers- and hard to get rid of once they bore inside the plant. They would do this to the cucumbers and basically live inside the veggie. So I have no cucmbers now, but they are still here and everywhere. I go out every morning and evening and I usually find them in the top leaves where the plant is growing from. I gently unroll the leaves and they are there. I then pick them and feed the lizards - my friendly garden pests, I have about 5 lizards hanging around and I set the worm down on the ground and the circle of life continues. I have tried BT and pepper sprays, my best defense is picking the plants as often as I can. They nest and have a white web (which it sounds like you found) sometimes they are so small you don't notice them till they eat half the plant and grow 3 times in size. Sometimes you can find a hole in the plant (I did tonight) and they bore inside, so I have to cut them out. I wish I could offer something better, but I live over on the Space Coast and they are horrible. I was hoping with the cooler spell they would go away, but not yet. I just applied BT tonight. Best of luck to you and again I could be wrong but I brought this up awhile ago and that seemed like the best info I got back.
I love this! - There can be no other occupation like gardening in which, if you were to creep up behind someone at their work, you would find them smiling.