Flies come in a lot of sizes, which makes some people think that they grow.  If it has wings, it is fully grown.  Small ones are just different varieties.  The large ones usually get identified by the patterns on their back, while the small ones are identified by the vein patterns on their wings.  None of them are cute.

Cluster flies are large flesh flies that breed in earthworms and swarm houses in the fall looking for a warm place to overwinter.

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If they find their way in, they will appear inside during sunny days when the warmth of the sun gets them moving, but it’s still too cold outside.

Once they get into a breeding mood, the next step is laying eggs.  In this case the female didn’t find a suitable place to lay them, so she wound up laying them on a window sill (after I sprayed her).

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When laid on meat, it looks more like this.

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Yeah, that’s a lot of maggots working over a dead possum.

When they are done eating, the maggots pupate, which looks like this.  These bred in trash cans in a garage, climbed out and crawled on the garage floor until they made it under the wall and fell into the basement, where they pupated on this sump pump cover.  Yes, we are detectives.

Smaller flies require a microscope for identification.

fungusgnat  Julie Smith fly

These are fungus gnats.

Care to guess what these are?

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They were breeding in standing water in a crawl space.  Larvae are in the water, adults are on the wall.  It’s tough to see, but some larvae have worked their way up onto the dirt and are pupating.  These people had a lot of drain (moth) flies, although this isn’t what we mean by “drain.”