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 (in the genus Eristalis), 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. I had originally thought that it was Eristalis tenax, which is a European import that BugGuide says is the most common one. However, it was pointed out down in the comments that Eristalis arbustorum looks like a better match, particularly the exact pattern of black on the abdomen, and what we can see of the pattern of hair growth on the eyes.

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. And, in fact, down in the comments Steve Sanford says he’s been raising these flies for 40 years, and does use them for orchard pollination whenever he has a surplus.

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.

27 Responses
  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


  11. Steve sanford permalink
    December 20, 2014

    been raising flower flies for 40 years weather related and difficult to raise , tenax are never used the die easily and are not to good to keep. I polinat apple orchars ever year if we have enough Steve

  12. December 22, 2014

    Thanks, Steve. Could you give some pointers on how you do it? Do you just create a good place for them to lay eggs and raise whatever the local flies are, or do you have a particular strain of flies that you maintain year-round?

  13. Jeremy permalink
    February 2, 2015

    Knutsons bait and tackle out of brooklyn michigan sells them and ships many other kinds of bait they usually have a lot of them in the winter because their normally used as an ice fishing bait.

  14. Randy Mcintyre permalink
    December 11, 2015

    How do you harvest the maggot from cow manure?

  15. December 11, 2015

    Well, I’ve seen them a lot in liquid manure, kind of floating around with their snorkels poking through the surface, and it would be easy enough to scoop them out with a coarse screen or net.

  16. G. G. permalink
    May 17, 2016

    I thought I would offer some input after reading some of the comments. I ordered a pack marketed as fishing bait from ebay. When they arrived I placed them in a plastic salad box (from Safeway) containing 1 cup of water and 2 tablespoons of bokashi compost. I put the salad tray on top of a larger tub containing moist, sterile coconut coir. Over the course of 2-3 days, several larvae climbed out of the water and into the coconut coir to pupate. About 70% of the larvae that came with the order were dead in 1-2 days after placing them in the water/bokashi solution. I removed the plastic tray and discarded the dead larvae after it was evident none were alive.

    6-9 days after removing the dead larvae, several adult flies started to emerge from the coconut coir. I am keeping them in a 5 gallon terrarium with a screen lid. For food, I have been feeding a mixture of 1:1 raw honey and water as a nectar substitute. I put the nectar/syrup in a used plastic (yogurt) container with the lid on and poked ~100 holes in the center with a insulin needle. I then invert the container and place on the screen to the terrarium. This creates little droplets of syrup, which the flies regularly visit for drinks. For a pollen substitute, I have been feeding ground Brassica napus (canola, rapeseed, etc.) pollen. Look for “Bee Pollen” on amazon or another marketplace, I got mine from a local apiary. After reading the Dolley et al. article posted above, I will try mixing the pollen 1:1 with sugar. It has been 5 days and all of the flies that hatched are still alive.

    I am still not sure the best medium for egg laying. I am avoiding human feces. I have a product called “Bug Burger” which is a for feeding crickets and other feeder insects. I made a batch of this and put just enough water to cover the food. I placed this in a small dish in the terrarium. I should know in a week or so if there are eggs.

  17. Derek permalink
    September 20, 2016

    I’m looking to raise my own “mousies”. I have some ordered. I raise red worms as well, so I’m going to prepare a container with composted moist peat moss as a substrate for the mousies, as far as the feeding goes, I know they like rotten, mushy apples, among other things. I will have a small tub of water in the container with them surrounded by the peat moss, so the larvae can choose which area they want to hang out in. For a nectar substitute, I will use honey and water. Do I need pollen to raise them, or could I put a few flowers in there for the flies to visit? I’m really hoping to get good results with this, any tips would be greatly appreciated!

  18. September 21, 2016


    I expect that you could use Bee-Pro pollen supplement for the adult flies:


    The 1-lb canister is not too expensive, and would be worth trying.

    Also, I would think that simple sugar water (sucrose) would be sufficient, since flowers produce sucrose in their nectar. When the bees convert it to honey, they split the sucrose into glucose and fructose. Since the flies are taking their food from flowers directly, they should be able to handle the regular sugar just fine.

  19. Derek permalink
    September 21, 2016

    Is the pollen absolutely essential for the flies or would the sugar water be sufficient? I’ve been told that they are impossible to raise and that has kind of discouraged me, but I want to attempt it.

  20. September 22, 2016

    They would need the pollen as a source of protein, which they won’t get from either sugar water or honey. They might survive a long time on just the sugar, but I expect their lifespans would be shorter and the wouldn’t be able to produce eggs.

  21. Derek permalink
    September 22, 2016

    Okay, I’ve prepared a 1 gallon container for the experiment. The bedding is moist peat moss/worm castings from my red worm composting. I put in some squished up apple pieces in there for them if they want to eat. Does this sound sufficient for the larval stage? I imagine they will eventually pupate below the surface of the peat moss. I have them at around 70 degrees or so. When the pupae form, I will move them to another larger container, with room for the flies to move around. I put a few flowers in there for the flies to get pollen from, sugar water, and a tub of the composted peat moss as a substrate for egg laying. Does it sound like I’m on the right track? Sorry for all the questions, but I really am hoping to be successful with this. Thanks again!

  22. September 23, 2016

    It might be enough, although every time I have seen the “mousies” in the wild, it has been in association with very wet manure (I’ve seen them in both cattle manure, and chicken manure). Rotting fruit is probably close enough to manure to work as well. I’ve generally seen the larvae right down in the wet and sloppy, but they haul up onto a surface to pupate.

    Anyway, what you are planning sounds reasonable for a start.

  23. Derek permalink
    September 28, 2016

    My original batch of pupae I put in the terrarium Friday afternoon, how long does it typically take for the drone flies to emerge? I’m not sure the larvae ate any of the apples I put in or the compost. They were in a moist, but not wet environment. Can they still be able to become flies if they did not eat while I had them? Next batch, I’m raising the larvae in an aquatic environment. So far, they are doing well in there, swimming around with their “snorkels” reaching up to the surface of the water, I’ll be watching for these to crawl up and pupate.

  24. September 29, 2016

    Derek: As far as I remember, it took around 10 days for the flies to emerge from the pupae. And, the ones I received in the mail were apparently pretty much mature, they pupated right away without eating much.

  25. Derek permalink
    October 2, 2016

    Great news! Two have emerged so far. I have not seen them really fly around or eat or drink yet, but I have everything in there, including fresh flowers for them to visit whenever they are ready.

  26. October 3, 2016

    Great! It sounds like you have a good start, hopefully they will have everything they need to mate and lay viable eggs.

  27. Derek permalink
    October 3, 2016

    I have the water and honey combo on the floor of the terrarium, that should be fine for them to feed, right? The flowers I picked are still all alive and one of the flies was on them today. Thanks again for all of the helpful tips, 2 out of the 6 emerged so far, hopefully a couple more will emerge any time.

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