FORTUNE -- To catch a bloodworm, you have to wade knee-deep in Maine mudflats and dig in the muck. Now, you have to be careful handling these creatures, which have alien-looking mouths and four black teeth that sting like a bee if they find their way into your skin. It may sound like an episode of "Fear Factor," but catching bloodworms is another day at the office for some Americans, and it's surprisingly lucrative. The worms are sold for bait, and 175 or so of them will bring in roughly $50. Bloodworm hunting is just one of the 300 dirty jobs that