n.
any one of several species of horsefly, usually very large and considered pests as females habitually inflict painful bites and suck blood from humans and livestock.
ENTRY IN PROGRESS
Type: 1. Origin — Early Canadian quotations (see 1792 quotation) liken the bulldog to the 'gad fly' in the UK. The OED-3 also mentions the gad-fly, and marks the term American. The first quotation in DARE is from 1893, so it is likely that the term originated in Canada and later was used in the US.
See also Gage-1, s.v. "bulldog2", which is marked "Canadian", ITP Nelson, s.v. "bulldog" (3), which is marked "Canadian", and OED-3, s.v. "bull-dog" (4a), which is described as American".