Drone fly larvae – “mousies”

2013 November 20

Some time ago, Sandy mentioned to me that the bait shops sometimes sold something they called “mousies” for ice-fishing bait. After she described them, I suspected that they were actually drone fly maggots, but we wanted to confirm this. So, last January, we decided to get some and see what they really were. None of the local bait shops had any on hand at the time, so we ended up ordering some through the mail, which we received on January 12, 2013. They were mixed in with sawdust, mainly just to keep them from banging around in the tubes.

The dark ones had already started turning into pupae, but the pale-colored ones would crawl around dragging their long “tails”. You can get an idea of their size by comparing it to the tip of my finger that is also in the picture. My fingertip is about 3/4 inch wide.

At this point, I was pretty sure that these were, in fact, drone fly larvae (Eristalis tenax), because we used to have them around on our dairy farm when I was a kid. Any pocket of wet manure or manure runoff water that was allowed to stand for more than a couple of weeks would soon end up full of these, which we called “rat-tailed maggots”.

The “tail” is a breathing snorkel, allowing them to immerse themselves in the most noxious, festering masses of decomposing manure imaginable, while still being able to poke out the snorkel and breathe. Other flies specialized in the drier material, but these were right down there in the soup.

For final confirmation, I put some of the maggots into a jar with some water and some chicken manure, which they lived in for a couple of days before making their pupae. Putting them into the wet environment appeared to be important, as the ones that had already pupated in the dry shipping tube never came out, while the ones in the wet jar emerged on January 30, 2013.

The resemblance of the adults to honeybees is pretty good. It is easy enough to tell them apart once you are familiar with them, but to a casual observer the drone flies look an awful lot like honeybee drones.

There are a number of generally similar bee-mimic flies, but Eristalis tenax is the most common one. Particularly if there are manure piles around.

Not only do these flies look like bees, they behave a lot like bees, too. They travel from flower to flower, drinking nectar, and transporting pollen. Which means that they are important pollinators. They are also easy to raise. Which suggests to me that people who have crops that they want pollinated might have an alternative to paying to have beehives trucked in. Instead, they could place buckets of slop filled with drone fly larvae, timed to hatch out when the plant they want pollinated blooms.

Pollination with honeybees is a big business. They get hauled all over the country to pollinate various crops, particularly almonds in California. The problem is, these traveling pollinators also carry around every honeybee pest and disease in existence, and are partly responsible for the rapid spread of the Varroa mites that have made hobby beekeeping such a dicey proposition. Which is why I kind of think that an alternative pollinator, which shares no diseases with honeybees, might be a better choice for providing pollination services as it would make it possible for the honeybees to stay home.

At this point you might say, “Great! Let’s try this! Um, but how do you raise these flies in captivity, anyway?” Well, you could do it using this recipe from 1933:

The flies are kept in wire cages, 15x15x15 cm, containing watch glasses filled with cheese cloth moistened with tap water. In these cages are also small wooden feeding troughs filled with a mixture consisting of equal parts of dry poppy (Eschscholtzia californica) pollen and powdered cane sugar. On this food, the flies live perfectly and lay many fertile eggs.

The cages are kept before a laboratory window but are not exposed to the direct rays of the sun.

The eggs are collected and placed on human feces in a vessel also containing moist earth. Fresh feces are added daily. The larvae pupate in the soil.

At a temperature of between 20 and 25 degrees C, a typical female began laying eggs 10 days after emergence and laid about 3,000 eggs in about 60 days. The eggs hatch in about 36 hours after they are laid. The duration of the larval and pupal stages is about 2 weeks and 8 days, respectively, at about 22 degrees C. Oviposition has been observed at various temperatures between 20.5 and 30.5 degrees C.

The pollen can be purchased from the Knapp and Knapp Pollen Gardens, North Hollywood, California, or it can be raised. The poppy blossoms are collected each day. The anthers are clipped off with scissors and dried in the sun for 12 hours. The pollen separated from the dried anthers by means of a sieve with a fine mesh is kept in a dessicator over calcium chloride. Pollen rapidly deteriorates on exposure to moisture.

(reference: Dolley, W. L., Hassett, C. C., Bowen, W. B., and Phillies, G. (1933), “Culture of the Drone Fly, Eristalis Tenax”, Science, Vol. 78, no. 2023, pp. 313-314)

The pollen might be problematic, although there is a good chance that the pollen replacement sold by beekeeping suppliers might work just as well.

10 Responses leave one →
  1. Menno Reemer permalink
    November 20, 2013

    Nice to hear about this vernacular name ‘mousies’, which somehow sounds more friendly than the usual ‘rat-tailed maggots’. I did not know these were commercially sold as fish bait.
    Please note that the adult fly on your pictures does not belong to Eristalis tenax, a species I know very well from Europe. Instead, I think it belongs to Eristalis arbustorum (a species occurring both in Europe and North America). However, I am not too familiar with the North American species of Eristalis. I think there is another species very similar to E. arbustorum occurring there, the name of which I cannot remember right now.

  2. November 20, 2013

    Menno: Thanks. I was basing my ID on two things: (1) BugGuide says that E. tenax was introduced to the US some time ago, and that it has since become the most common species of drone fly here, and (2) I thought that E. tenax was the preferred species for people who wanted to cultivate drone flies. Looking at the pictures, I see that it could easily be E. arbustorium, although to be honest I don’t think I could tell the two species apart if my life depended on it. Could you let me know what ID feature you used to determine that it wasn’t E. tenax?

  3. November 20, 2013

    “For final confirmation, I put some of the maggots into a jar with some water and some chicken manure…”

    That sentence, I expect, is very rarely used: I admire your dedication to scientific pursuit!

  4. Carole permalink
    November 20, 2013

    Most interesting post. I think a problem with replacing flies with honey bees is they aren’t considered very efficient pollinators. Would be a good subject for a science fair project.

  5. November 21, 2013

    Andy: Speaking of dedication to scientific pursuit, I just added some instructions for cultivating drone flies in the lab to the post. And I’d like to call attention to one particular quote from it (emphasis mine):

    “The eggs are collected and placed on human feces in a vessel also containing moist earth. Fresh feces are added daily. The larvae pupate in the soil.”

    While I’m sure that any number of other kinds of manure would do as well, the human feces have the advantage that any lab staffed by humans will always be able to get some, provided they can overcome their squeamishness. And don’t mind the smell.

  6. November 21, 2013

    Carole: That’s a good point, but sometimes I wonder if it isn’t so much that flies are less efficient, as that the bees have an entire industry producing better propaganda for them.

    It would be a good science fair project, if one could work out a way to test it on a shoestring budget. For that matter, it might be a good project to submit to the NSF or Department of Agriculture.

  7. Jason Sauve permalink
    November 26, 2013

    So just to be clear, what kind of substitutes could be used for the pollen to raise these? Also, I’m quite sure these can be raised in moist grain.

  8. james hobencamp permalink
    January 20, 2014

    hi i would like to purchase about 5000 of the larvae a year . starting around november . does any one have them to sell or does anyone know where i can by them . thanks jim

  9. January 20, 2014

    Well, I’ve never bought them in bulk, but I’ve seen these two wholesalers recommended:

    http://www.wholesalebait.com/ (seem to be sold out for this year, but might be able to get you something in November if you order them now)

    http://www.vadosbait.com/ (not sure they have drone fly larvae, they just list “maggots)

    I also found this article about mousie availability, there’s aparently been an ongoing shortage since last year:


    It seems that most mousies aren’t actually purpose-cultivated under controlled conditions. Instead, they are harvested from “wild” populations in places like vegetable cannery waste ponds and manure pile runoff. And for the last few years, the commercial cannery waste ponds have been being cleaned up due to environmental regulations, while the farm runoff ponds have been drying up due to ongoing drought conditions in most of the country. So, no mousies.

    This could be a good business opportunity for someone to go into the mousie cultivation business. It’s easy enough – last summer we had a tub of stagnant water filled with chicken manure, and by about August it was loaded with them. You could probably get a few thousand breeding in a cheap wading pool filled with manure-saturated water.

  10. james hobencamp permalink
    January 27, 2014


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