For what it's worth, earthworms are often on peoples 'safe' wild caught food lists so I've always assumed they're low on parasites that can affect amphibians but don't know for sure. For example http://www.frogforum.net/tree-frogs/...ght-foods.html and FEEDERS: Collecting Earthworms - Â*BambooZoo. I've also used wild caught night crawlers for years with no issues (with treefrogs, I've no experience with horned frogs). Make sure you're collecting from a chemical free area though if you go this route.

These people are located in Alaska and sell Red Wrigglers (though they don't give the scientific name but Eisenia fetida are the usual suspects for composting): Buy Worms And Bins » Worms And Stuff so shipping would likely be cheaper than ordering some version of night crawler from the lower states. But do take Carlos' post into consideration if you opt to try Red Wrigglers.