death's-head : Idioms & Phrases

• noun European hawkmoth with markings on the back resembling a human skull
  Acherontia atropos.
  

WordNet

• (Zoöl.), a very large European moth (Acherontia atropos), so called from a figure resembling a human skull on the back of the thorax; called also death's-head sphinx.

Webster 1913