Medo, hard to tell from the picture-can't enlarge it..are the caterpillars striped black/gold-green and white? If so, they are to turn into Monarch Butterfly, milkweed being their favorite host plant, also Passion vine-in here anyway. I think you'd already know it, but never can be sure, took me years to realize what was eating my parsley weren't just any caterpillars, I was geting rid of future butterflies, oh well, garden and learn.----Bea

Hey!! Is it aphids? Aphids come in many different colors, and they like many different plants. They will totally stress out your plants. You can spray them off with soapy water. Sometimes I squish em with my fingers! gross I know, but I hate chemicals, cuz they kill good bugs too - Sha

I was thinking the same as Sharon medo,looks like a clump of green aphids to me. I do it just like Sharon....squish!

On second look they don't resemble caterpillars at all...you might be right, could be aphids, I just never seen them anywhere on milkweed except the tips , among the buds. Nothing wrong squishing them with gloved hands and spraying with soapy water.