During the Eocene Epoch (57.8 to 36.6 million years ago), gars lived in Europe as well as in North America. One reason for their survival is thought to be that their relatively large, yolk-filled, greenish eggs are highly toxic to prospective predators. The eggs are laid in shallows in the spring; the hatchlings grow remarkably fast, feeding from the start on the hatchlings of other fish and even minnows, and soon become such voracious predators that measures are often applied to reduce their numbers. The long rows of needlelike teeth are very effective in capturing prey. The beak is very long and forcepslike in the longnose gar, or billfish (Lepisosteus osseus), but broad and relatively short in the alligator gar (L. spatula) of the southern United States. The alligator gar, reaching a length of about 3 m (10 feet), is one of the largest of all freshwater fishes. Gars are edible but are almost never eaten in the central and northern United States. They are sometimes baked in their own armour. Some artisans fabricate the enameled scales into novelty jewelry.

Especially in Europe, the name gar, or garfish, or gar pike, is applied to the needlefish (q.v.) of the family Belonidae. In Australia the term is used for the halfbeak (q.v.), a relative of the needlefish.