Length: fly in photo 4.5 mm
In the family Acroceridae, the calypters are notably large. As the common name says, the head is small (consisting of little more than the eyes), and it is low compared to the thorax. The antennae are three-segmented.
The pattern of wing venation is often simple. The body is essentially without bristles.
In profile, most Acrocerids look hump-backed.
Larval Acrocerids are internal parasites of spiders in the order Araneae. Some authors have used the common name Spider Flies to refer to Acroceridae.
A female Acrocerid lays up to 4,000 eggs; the location and manner of oviposition varies by genus and species. Members of the genus Acrocera oviposit on green grass stems, placing the eggs in "a linear spiral" (McAlpine et al., 1981).
Evert I. Schlinger, writing in Brown et al. (2009), states that the only exception to the internal parasitism is in an undescribed genus from Chile. In that genus, the larvae feed on a living spider while externally attached.
Genus Acrocera is found nearly worldwide, missing from only Madagascar and the region of Australia. There are a total of fifty-six described species. Sixteen species live in America north of Mexico. Thus far only four species of Acrocera have been described from the Neotropical region.
Note that this is both the family page for Acroceridae and the species page for Acrocera bimaculata.