Sorry, no wild silkworms
Hi - the silkworms we use as feeders for our herps are the same species that are primarily used in the silk industry. Their scientific name is
Bombyx mori and they are of the family Bombycidae (I am not doing this to give a lesson in Latin or Greek,

but to clarify.)
They have been cultivated for thousands of years for color and strength of the silk they produce. They are no longer able to live in the wild (again, for centuries+) and are strictly raised by humans. We do have wild silk moths in North America and elsewhere in the world; they are in the family Saturniidae. Most people know the luna moth and polyphemus from this family; they are very large (up to 6+" wingspan) and (most) fly at night. They make large cocoons and their silk is used too, but for different markets in the industry. They are not bred on a large scale for this purpose.
OK, now that you know they were definitely not
B. mori they might be on of the Saturniidae. The Saturniids do not congregate to spin as you have described. If I am understanding your description you mean there is one large silken structure (usually in the crotch of tree branches or at the tips) with many caterpillars inside? Or are they spinning individual cocoons (one caterpillar per structure)? Also, where do you live? It could help narrow it down. Any chance of a photo? Of the Saturniids, the cecropia and polyphemus are know to feed on elderberry (but there are a lot of other caterpillars that do, too). Unless you can make a positive i.d. I would not feed them to your cham. Many have urticating (stinging) hairs and spines, others are toxic. If they are of the Saturniidae family you will probably not want to raise them as the process from egg to adult can be a full year (species and location) and definitely not practical as a feeder (and again, some may be harmful to your cham).
If they are in the "communal" web then they would likely be fall webworms, gypsy moth or tent caterpillars, again, depending on where you live.
Rather then link you to a bunch of pics, a Google image search it will result in many photos
Hope this was helpful and not too boring

I have been raising the Saturniids for several years and know other moths, too.
lele