Up here in Arkansas the first ones usually appear in late June and early July. Look for Catalpa trees in your area ahead of time and secure permission early. Watch them and the worms will eat the leaves . I wait till the worms are big , but don't wait too long as they leave to make cocoons. They are great baits for all kinds of fish. They are best live , kept in a cage with leaves from the Catalpa tree. If you get extra worms , they can be frozen. It's best to blanch them first. We boil a pan of water and then drop them in for just a few seconds to kill them. Drain on paper towels till cool. Place in small ziplock type bags in small quanities. Freeze these for later use. We use them for catfish mostly. I've caught crappie ,bream , saugeyes , bass , and catfish on these worms. But the fresh live worms are always best .
Good luck with finding the worms. Hope you catch a bunch of fish .:D