Super-Mutant Fruit Flies on Steroids!

Scuttle Fly

I recently mentioned that I’ve been having a bit of a pesky fly situation in my indoor worm bins – which has led me to take a cautious approach with my new VB48. For the life of me I couldn’t figure out what type of fly I had – but I knew they were something I hadn’t encountered before. For one thing, I was finding them all over the place – including our kitty litter boxes! But, they also exhibited some weird behavior.

They reminded me of giant fruit flies (Drosophila sp., that is ) – yet they seemed to do more running around than flying. I also couldn’t seem to trap them in my cider traps. Finally, late last week I figured out what they are…

Scuttle Flies – A.K.A. “Humpback Flies”, “Coffin Flies” (Family Phoridae)

I’m even pretty sure I know what species I have – Megaselia scalaris. This seems to be one of the more common/widespread varieties of Phorid flies, and the image on the Wikipedia page is spot on.

Reading the various descriptions of scuttle flies I came across helped to strengthen the concerns I already had. For one thing, their complete lifecycle (time from eggs to adults) – while not nearly as fast as that of fruit flies – is only around 20 days or so. This seems to be on par with fungus gnats (and we know how much fun they can be! lol).

Probably more alarming, though, is the fact that the larvae are more opportunistic in their feeding preferences (than fruit flies) – being comfortable with consuming a wide range of decomposing organic matter. In other words, once these guys are established in composting systems, it’s likely going to be a lot more difficult to get rid of them.

Megaselia scalaris

These flies can apparently be pests in mushroom growing operations. I came across some articles mentioning attempts to control them with parasitic nematodes (Steinernema feltiae), but the consensus seemed to be that this approach was only moderately effective, at best.

Nevertheless, that does at least give me a place to start. I placed my order for more S. feltiae on Friday, and they are scheduled to arrive tomorrow!

I’ll admit – Megaselia flies do actually have a few things going for them.

1) Like I said, they tend to “scuttle” when disturbed, rather than fly off. This, combined with their larger (than fruit fly) size makes them an easy target for the “swat team” (yuk yuk). It also makes them FAR less annoying than fruit flies (no clouds of them in your face when you open your bin).

2) Their larvae and pupae are much larger, and thus easily found in your system. This makes it easier to physically remove them, and to just generally to determine how badly infested the system is.

3) The adults are active feeders, so my hunch is that I can come up with some sort of effective liquid trap for them. A lot of Phorid fly adults feed on sweet liquids – so I may try honey and/or maple syrup, molasses etc. Megaselia adults are reported to feed on various protein-rich liquids as well, so I may try something like a yeast suspension.

Scuttle Fly Larvae and Pupae

Scuttle Fly Larvae
Scuttle Fly Pupae

According to Wikipedia, there are about 4000 known species of Phorid flies, including the “world’s smallest fly” (0.4 mm), and the “ant-decapitating fly”, Pseudacteon – which offers some promise as a biological control agent for fire ants (I can almost hear the cheers of all you southern vermicomposters! lol)!

My primary focus right now is on making sure my VB48 doesn’t become overrun with these guys. I ended up stocking the bin with worms earlier than planned (will write more about that in my next VB48 update) largely due to the fact that I want my worm population to help keep the flies in check (by competing with the larvae). Ironically, by adding the worms I also added a culture of these flies, since they had invaded the two bins I dumped into the VB48!

Seems kinda counter-intuitive (or just plain DUMB! lol), I know, but I still think I can keep them from getting out of hand if I let the worms go crazy in their new home right away. One of the downsides of letting any system “age” is that it can be a prime opportunity for other critters, such as fruit flies, to become well-established.

Anyway, now that I KNOW what I am dealing with here, I feel a lot more mellow about the situation, and a lot more optimistic about my chances of keeping these pesky critters under control. Worse case scenario, the experience will at least help to educate my readership about these flies!

Stay tuned!

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    • Brett Sutherland
    • November 12, 2012


    I run a worm farm project at Rhodes University. I have been having major problems with these flies, which I thought were just normal fruit flies myself. I was wondering will fly paper help. It was previously suggested that i use vinegar in a suspended bottle which they would get attracted to, however this was a epic fail. If you find out how to get rid of them please let me know. Thanx for the rticle

    • Ben
    • November 12, 2012

    That’s a very interesting write up, and thank you for keeping us posted on this. I have fears of bugs in my house, as you well know, due to previous infestations. I don’t think my marriage would survive clouds of bugs this large. At least not with me still sleeping in the house!

    I’ll be looking forward to your future updates on types of traps you use and how effective they are. Who knows, maybe the mushroom industry will be looking to you to solve their problems soon. 🙂

    • Bentley
    • November 12, 2012

    BRETT – Good question about fly paper. I haven’t noticed any attraction to light with these flies (unlike fungus gnats) so it might be challenging to lure them towards the paper. Also, the fact that they like to run around a lot rather than fly might make it more challenging! BUT this has me thinking of something else! What about something like “tanglefoot”?
    People have told me it’s pretty effective for gnats and fruit flies, so it might be something especially helpful with these guys.

    • Bentley
    • November 12, 2012

    BEN – Keep in mind that these shots were taken using the macro setting on my digital camera. These guys are basically just like fat fruit flies. Of course – given the fact that fruit flies are super annoying and noticeable – that’s still big enough! lol
    I think it’s basically taken me (almost) 13 years to get these flies – and I’ve likely had at least one or two fruit fly infestations each of those years (lol) – so hopefully that means your chances of ending up with these guys is a lot lower.

    Anyway – I’ll see what I can figure out!

  1. I contacted you back in August, having a problem with “Giant Vegetable Flies” – they seemed to be focused heavily on decaying squash and potatoes, not at all interested in wine or vinegar traps. I am pretty sure these are the same thing.

    The most effective treatment I found (aside from locating the potatoes that had gotten shoved back behind the cereal in the counter, and eliminating Ground Zero) was a small vacuum – they don’t fly fast, and I could usually suck them up with the hose before they even took off.

    • John Duffy
    • November 12, 2012

    Swat team…. Good one!
    Larry Duke will be your bestest friend if you can get him a few thousand ant decapitating flies…I wonder if they like spiders too?

    • John Sliwinski
    • November 14, 2012

    I have been using a layer of screened compost over top of every tray I add to a WF360. This seems to be very effective with fly problems. In the past I used a bug whacker above the bin that did a nice job with fly’s that are attracted to light. Another idea I had would be to build a simple screened box to enclose the bin till the problem dissipated.

    • The Garbage Guru
    • November 15, 2012

    John supposedly we got the decapitators here.Lol! But they are identified by the same skipping like motion as the ones Bentley has.Guess i’m gonna need a bigger magnifying glass.Or look for fire ants walking around without a head.Lol!

  2. Ive been hanging sticky fly traps above the sinks in my bathroom and kitchen. I also have one hanging above my worm inn in my “worm room” (a bathroom I gave to the worms) and this particular sticky trap is covered in these flies. They are attracted to the color yellow and I found them drowning in urine after my kids forgot to flush. Cutting the lid off of a water bottle then turning the lid upside down so that the neck pours back into the bottle is an easy DIY trap, you can put some honey water in the bottle and the flies will get trapped easily inside. You can hang these little 1 or 2 lit traps anywhere you need them 🙂

    • Bee
    • June 21, 2013

    I have a worm bin in my kitchen and have been fighting with an outbreak of flies (I assumed fruit flies) for the last 2-3 months. They don’t really seem to be attracted to apple cider vinegar or commercial fruit fly traps, though they do hang out in my skylights in droves. I haven’t seen much evidence of them around the worm bin, and I’ve cleaned up every source of food I can find, and stir up the bin often.

    Any hints on getting rid of these pests, other than vacuum up the adults and hit any I can reach?

    Thanks! Your blog has been a great help with my bin and a project for work!

    • Bill
    • December 7, 2013

    Thanks so much for the detailed info. I had these flies in the house this summer/fall and was curious what kind of fly they were. I noticed their running habit and that they didn’t go to the vinegar fruit fly traps. They were never problematic, but interesting.

    • Owen
    • March 16, 2014

    I’ve been running a small DIY flowthrough system for over a year now, and just started seeing these guys this week after a bit of warm weather. I’ve had a few different fly invasions before (vinegar flies, white flies, and fungus gnats) and I’m dealing with this one much as before, by beefing up my surface bedding and laying down some layers of newspaper on top to try to exclude adults from the underlying bedding.

    As with all fly invasions I also try to reduce the adult population by getting them out of the bin by taking off the lid and shooing them off the top, and then closing it up before they can fly back in (my unit is outside). With these ones I’ve noticed that this strategy doesn’t work as well, because they like to run instead of flying. However, since they like to congregate on the lid, I’ve found that if I just bang the lid on the ground a few times, I can knock them off without them taking flight. It’s easy work to finish them off with a sneakered or sandaled foot. This might work better in cooler weather, as I can imagine they are slower and less likely to fly.

    Anyway, thought I’d pass on this simple method in case anyone else has a similar issue.

    • Anthony
    • September 15, 2014

    These fly’s are attracted to carrion where they feed and lay their eggs.

    A few dead worms in a small punned buried in the bedding slightly higher than the surface will draw them in. They will lay their eggs close to the dead worms. The fact that they rather run than fly makes them suckers for these types of traps! You get the adults and the larvae in one swoop. Quickly put the lid on the punnet and you’ve “Got Em”.

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