What is "blister fly"

Blister \Blis"ter\, n. [OE.; akin to OD. bluyster, fr. the same root as blast, bladder, blow. See Blow to eject wind.]

1. A vesicle of the skin, containing watery matter or serum, whether occasioned by a burn or other injury, or by a vesicatory; a collection of serous fluid causing a bladderlike elevation of the cuticle.

   And painful blisters swelled my tender hands.
   --Grainger.

2. Any elevation made by the separation of the film or skin, as on plants; or by the swelling of the substance at the surface, as on steel.

3. A vesicatory; a plaster of Spanish flies, or other matter, applied to raise a blister.
   --Dunglison.

   Blister beetle, a beetle used to raise blisters, esp. the Lytta vesicatoria (or Cantharis vesicatoria), called Cantharis or Spanish fly by druggists. See Cantharis.

   Blister fly, a blister beetle.

   Blister plaster, a plaster designed to raise a blister; -- usually made of Spanish flies.

   Blister steel, crude steel formed from wrought iron by cementation; -- so called because of its blistered surface. Called also blistered steel.

   Blood blister. See under Blood.