mule killer

from The Collaborative International Dictionary of English v.0.48

Mule killer \Mule killer\
   Any of several arthropods erroneously supposed to kill live
   stock, in the southern United States, by stinging or by being
   swallowed; as:
   (a) A whip scorpion. [Florida]
   (b) A walking-stick insect. [Texas]
   (c) A mantis.
   (d) A wheel bug.
       [Webster 1913 Suppl.]