Some of the largest flies in the world belong to a family called (believe it or not) Pantophthalmidae. The tongue twisting nature of this name aside, the English name “giant wood-boring flies” seems less impressive. They are found only in the Neotropical Region (South and Central America), where they are uncommonly collected, usually at light or on freshly cut wood. Although frighteningly large, these flies are utterly harmless. Their larvae, however, bore into dying or dead trees eventually growing to a large enough size to produce the iconic adults.
I have seen exactly two living adults of these flies, but recently in Costa Rica, we came across evidence of many more. We were staying at a resort oriented towards birders called “Hacienda Baru” that is situated close to sea level on the Pacific coast near Playa Dominical. It was hot and humid there, and the biting midges were fierce, but we made it through a few days before fleeing to the highlands.
Along the trails were logs cut from tree falls, and in some of them were living and freshly abandoned pupae of pantophthalmids. In the log photographed here, I counted 65 exit holes alone, and some other trees in the vicinity had hundreds of holes drilled by the larvae of these flies.
For those interested in encountering large numbers of giant wood-boring flies, Hacienda Baru should be the first place on your list!
(I thank Kirk Fitzhugh for the first image).