Bt will kill most any caterpillar (except maybe army worms) but there are many good caterpillars around this time of year too so great care is needed.

For example a "striped black and yellow" one can be a swallowtail butterfly. Without a photo of the caterpillar in question it would be impossible to ID it but there are plenty of photos on the web available for comparison.

Linked photos of bagworms below.

Dave

Here is a link that might be useful: Bagworm pics

Thanks, Dave. I'm pretty sure they are Eastern Tent Caterpillars. Still haven't identified the cocoons that were under my nylon net. They look nothing at all like the ETC's cocoons. I will continue searching pictures of cocoons on the 'net.

Madonna

Tent caterpillars that are striped yellow and black? It doesn't sound like tent caterpillars. But presumably you've looked at photos. To answer the other part of your question, no they aren't all related. At least not any more than all birds are the same. Various caterpillars favor different foods and have different degrees of "pest-ness", and plenty turn into wonderful butterflies and moths. Your cottony coccons could maybe be the work of the cabbage moth, especially if the corn is handy to the brassicas. Or it could be one of the untold hundreds of small moths and butterflies that go unidentified by most since they don't get up to anything bad in the garden.

Found out that the unidentified cocoon in my previous post is from the gypsy moth. Got my Purdue Extension newsletter today which had a picture of it as well as the history of the gypsy moth. Seems that our state has been hit with infestations of them this year.
Madonna