Numbers
Nearctica lists 3 species.
Remarks
From
Gerard Pennards: "they belong to the family Chloropidae, so the Frit flies! One of the characteristics of this family is the big ocellair plate on top of the head, which is very good visible on the fly in the middle of the picture.
This is very interesting, because most species in this family are phytophagous. There are some that feed on other stuff, and even some that are predacious and feed on eggs in a wide variety of egg sacs (spiders, Lymantrid moths and mantids), just as this one.
So this one belongs to the genus Pseudogaurax, of which there are 3 species in Southern USA!"
From
R.L. Smith, 1982: "These include a mud-daubing wasp (Chalybion californicum) that hunts adult spiders to feed its young, and a tiny fly (Pseudogaurax signatus) that lays its eggs in a partially completed spider egg sac. When the egg sac is finished, the fly larvae hatch and feed on the spider's eggs, but not all of them. The flies need some of the spiderlings alive to dissolve an exit hole in the sac so they can escape."
Terry Wheeler: Diversity and Host Associations of Pseudogaurax, Predators of Arachnids
Abstract 11/2003
Larvae of Pseudogaurax are predators of spider egg masses, with records from several host species. There are also records from eggs or cocoons of three insect orders and this talk documents the first record from an adult amblypygid (tailess whip scorpion) in Costa Rica. Adults were collected in the past, but ongoing inventory work has revealed several new Neotropical speicies and Pseudogaurax is clearly more diverse than realized.
