Worms don't got legs, that's one of the distinguishing characteristics when classifying critters. Now lots of folks call any long squirmy things worms, the inch worm is a caterpillar for example, so no problem. Sounds like a Water Tiger, the larva of theGiant Diving Beetle. Is this it? http://www.royalalbertamuseum.ca/natural/insects/bugsfaq/diving.htm http://www.whatsthatbug.com/2007/10/29/water-tiger-predaceous-diving-beetle-larva-and-you-can-eat-it/ A truly viscious beast that can eat things way bigger than itself, other invertebrates and even fish, so watch where you keep it. They can wipe out an aquarium B4 you know what is happening. I speak from experience. It was small when I put it in there, I thot the fish would eat IT, there were some 6 inch fish in there. Then smaller fish started dissapearing, then larger ones, then I saw this huge ugly thing hanging onto one of the big fish. The tiger larva does have 'mandibles' (chewing jaws) but two curved fangs, it pierces its prey, injects some digestive juices and drinks the blood and liquified parts. Tiger? Its a water vampire! I'll try to post pics, but I haven't had much luck with that lately.