Sunday, January 30, 2011

Scuttle Flies

Have you ever noticed how there are these little tiny flies that run, stop, and run in a seemingly random fashion around your kitchen or bathroom? Sorry, I sound like Andy Rooney. Well, they are not schizophrenic “fruit flies,” but a different kind of fly altogether. Scuttle flies belong to the family Phoridae, and are also known as humpbacked flies or coffin flies.

The most common species of phorid by far, at least in the urban environment, is Megaselia scalaris. Males are roughly two millimeters long, females about three, so if they didn’t move you might not even notice them. They are also very easily confused with vinegar flies (aka pomace flies) in the family Drosophilidae, which we call “fruit flies.” I’ll point out the differences shortly.

I habitually find Megaselia scalaris around the garbage disposal in the kitchen sink. This should not be surprising. The larval flies feed in a variety of decaying organic matter. These little maggots might drown in the drain trap, but they can swallow air to make themselves buoyant and avoid that fate.

Dr. Brian V. Brown, an entomology curator at the Natural History Museum of Los Angeles County, is one of the leading authorities on the family Phoridae. While 90% of the specimens he is asked to identify turn out to be Megaselia scalaris, there is an enormous number of undescribed species, even within the genus Megaselia, which accounts for about half the species in the family.

It is important to note that even the cleanest homes and businesses are bound to have scuttle flies at some point, and they rarely reach population levels that make them any more than a nuisance. They present no health threat to the average person, but they have been recorded as infesting wounds in hospital patients. This phenomenon is known as “myiasis,” and is exceedingly rare. Check out This abstract if you want the gory details of an example from overseas.

The vinegar flies in the Drosophilidae family are probably a little more common than phorids in the average house, but with a little practice you can easily tell the two apart. Above is an image of a Drosophila. Note the large head in proportion to the body, with bright red eyes. Scuttle flies, like the magnified specimen shown below, have smaller heads with dark eyes. The “thighs” on the hind legs are heavier than those of vinegar flies, too.

Still, behavior is the biggest clue. Scuttle flies run in a darting fashion, only flying if dodging you on foot doesn’t work. Vinegar flies perch, and while they may walk slowly, never seem to run. Their instinct is to fly to avoid a potential threat.

Sources: You will find this link from Bugguide.net to be helpful in learning more about these common yet fascinating flies. The chapter on Phoridae in the Manual of Nearctic Diptera is in volume 2, now available as a free PDF download. The Manual is the reference to North American flies, even though it is already somewhat out of date.

14 comments:

  1. This is great! I have seen these flies and always considered them to be Fruit flies!

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  2. These are great little guys. Thanks for sharing the photos and article.

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  3. Good blog post Eric. I think I may have seen these scuttle flies in my house just recently. They seemed a little different than the vinegar flies we usually get. Now I will have to investigate further.

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  4. Is the Scuttle fly likely to be the ones that like to crawl around on my computer and television screens at night?

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  5. Elliott: It could very well be these flies you speak of, but without seeing actual specimens I can't reach a concrete conclusion.

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  6. Thanks, I will certainly keep an eye out next time. Thanks for the great blog, so excited I found it!

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  7. Can You Help? I saw you offer a comment on someone post & was hoping I could pick-your-brain?
    At first I thought fruit fly, then some kind of knat, now I'm just fustrated & getting really tired of these little bugs. I have a piture of them (not sure how to upload to you), but they are "really tiny" (pencil-dot) , FAST (flying), seem to Jump, Love the light, and when flying sometimes seems neon (greenish-yellow) in color, but I don't see that color when they are dead.
    I am in college full-time and spend A LOT of time on my laptop with the lamp on; so they get in my face A Lot! I end up eating them (ICK) or getting them in my nose/eyes!
    I can't take it anymore, PLEASE Help Me!! :) Thanks, Anne T

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    1. Hi, Anne: I strongly suspect you are describing very small leafhoppers (family Cicadellidae) in the tribe Empoascini. They are simply overwhelmingly abundant for short periods of time, and yes, strongly attracted to lights at night. They are small enough they can squeeze through the mesh of window screens. I recommend closing windows, replacing worn weatherstripping around doors....and being tolerant. They'll disappear just as quickly.

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  8. how can i get rid of these scuttle flies? i don't have any potted plants, and I dont appear to have any water leaks, so I'm not sure of the source!

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    1. Most of the time, the problem resolves itself, with no intervention. Try cleaning the garbage disposal in the sink (run some orange peel through it, makes it smell better and the citric acid repels most insects). Take out the garbage frequently if you are disposing of food daily or nearly so. Not sure what else to recommend beyond that.

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  9. I have had little files similar in size to fruit flies, but brown and they don't have red eyes, that seem to appear every year. I find them in the bathroom and kitchen the most, but I see a few flying all over, but they bite, and I seem to have a reaction to them. What r they, and how do I get rid of them??? Plz help! Every other fly I've looked into do not bite humans.

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    1. Without seeing at least a clear image (preferably a specimen), and knowing where on the planet you are located, I cannot answer your questions. Scuttle flies do not bite.

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  10. This guy a scuttle fly? He's got long legs and little white marks on the back, but I was having trouble seeing his wings. (zoom in to see better) . Thanks!
    https://www.flickr.com/photos/159517907@N06/36937835870/in/dateposted-public/

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