The Collaborative International Dictionary of English v.0.48:

Thunderworm \Thun"der*worm`\, n. (Zool.)
   A small, footless, burrowing, snakelike lizard (Rhineura
   Floridana) allied to Amphisbaena, native of Florida; -- so
   called because it leaves its burrows after a thundershower.
   [1913 Webster] Thundery