Well over 1,000 species in North America
Typical adult Muscoidea are yellow, gray, brown, or black, with 1-2 presutural and 3-4 postsutural dorsocentral bristles, wing vein Sc separate from R1 and ending in wing margin, wing vein M nearly straight or gradually curved at tip, abdomen with short bristles, and some to many bristles on tibiae. There are exceptions, including the common house fly which has a sharp bend in vein M. Most larvae are typical maggots. Fanniidae are flattened with long spines.
Larvae may be predatory, saprophagous, coprophagous, or occasionally leaf miners.
As treated here, this taxon is artificial: the monophyletic Fanniidae are sister group to the rest of the muscoids plus the Oestroidea. The Muscidae are monophyletic and sister to the Scathophagidae+Anthomyiidae+Oestroidea clade.(1)