The Collaborative International Dictionary of English v.0.48:

Sphex \Sphex\, n.[NL., fr. Gr. ???, ???, a wasp.] (Zool.)
   Any one of numerous species of sand wasps of the genus
   Sphex and allied genera. These wasps have the abdomen
   attached to the thorax by a slender pedicel. See Illust. of
   Sand wasp, under Sand.
   [1913 Webster]

   Sphex fly (Zool.), any one of numerous species of small
      dipterous flies of the genus Conops and allied genera.
      The form of the body is similar to that of a sphex.
      [1913 Webster]