Parasitic Wasps for Controlling Flies.


I’ve been struggling with vats of flying, stinking, green bottle flies since the day I got chickens.  They swarm and annoy and worst of all they’re G R O S S.  Way worse than house flies.  A house fly is like an annoying teenage girl who says “like” every second word.  Bottle flies are like an ever growing gang of 15  year old boys with a pack mentality, screaming f*ck at the top of their lungs at 2 in the morning and peeing into mailboxes.  In other words, WAY more annoying.

Plus of course, bottle flies are dirty (they breed on poop, then fly over to your cob of corn and walk all over it) and they have the potential to kill your livestock through flystrike.

For years I’ve made and used these DIY fly traps which actually work GREAT but are a bit gross.

I’ve decided that instead of trying to fight these flies with traps and sticky tape I’m going to just let nature take its course.  If you can’t beat ’em, join ’em.  Live and let live and all that.  In fact, as an apology for all the trapping and sticking I’ve tried to do,  I even got the bottle flies some friends to play with!  I ordered them special.  Bug buddies!


The fly parasite is actually a parasitic wasp.  I was so sure they’d get along with my bottle flies, but as it turns out … fly parasites actually attack and kill bottle flies.

Who knew?  I did.  Because reader Shauna Henry told me so last year. She uses them in her chicken coop.

I ordered 10,000 of them.


You can get delivery of 10,000 parasitic flies for about $20.  How they work is they attack bottle flies when they’re in their pupa stage.  The parasitic wasp burrows into the bottle fly pupa, kills it, then moves on.  Over and over again. So the bottle flies are killed even before they become flies. So tragic.

Gosh.  And I thought I was just inviting over a few friends for my bottle flies.  Instead they were all killed in a homicidal frenzy.  Such a shame.

Depending on how many flies you have, you need to get delivery of new fly parasites every 2-4 weeks through the summer.


There are a lot of companies online you can order them from. Here in Southern Ontario I got them from Bugs for Bugs, Natural Pest Management.



The fly parasites are gnat size parasitic wasps that are nocturnal and don’t bother with humans at all.  All they want to do is attack and kill fly pupa.  They’re good like that.


The fly parasites arrive at your house in a small bag, in small box a couple of days before they’ve hatched.  You just sprinkle them around the bottle fly gangland and wait.


Because I have chickens who are notoriously curious and hungry (Norma the chicken once proved this when she lunged at me and ripped a half carat diamond earring out of my earlobe), I did my best to hide the fly parasites when I sprinkled them. I put them under the poop board and behind boxes in the run and anywhere I could find that they’d be protected until they emerged.  Fly parasites are incredibly effective killing machines, but they can’t do much of anything if they’re in your chicken’s gizzard.


I sprinkled them around the edge of the coop …


… on their ladder steps …


… under their poop board.


Just days after I added the fly parasites to my coop area it got REALLY hot here in Southern Ontario.  Crazy hot.  Idris Elba hot.  Which happens to be the preferred weather condition of bottle flies.  Normally when it heats up bottle flies seem to multiply within minutes, covering everything in sight with their bottle fly rave dance party.  I hate them.

But this year when the weather heated up there wasn’t a fly to be found.  Well, there were a couple but not many.

Conclusion?  Fly Parasites seem like something out of science fiction.  And they are. And that’s probably why they work.  It’s nature versus nature just like on an episode of Mutual of Omaha’s Wild Kingdom.  And like that tv show I gave nature a little bit of a hand, by bringing the fly parasites in myself. I basically let nature take it’s course, I just made sure there was a fair fight.

I’m still going to make my old fashioned fly trap, because I still want to trap the few flies that escape the fly parasites.  It’s always good to use at least 2 methods when you want to protect yourself.  Any well seasoned lady of the evening will tell you the same thing.

I’ll keep getting delivery of these fly parasites every 3 weeks throughout the summer and that should keep the bottle fly population quieted down quite a bit.  I’m encouraging my supplier to come up with a 15 year old boy parasite to quieten them down but so far no luck.

Like, I’m not even, like, sure a, like, 15 year old girl would, like, do the trick.







  1. Amy W. says:

    We have regular flies (not sure they’re green bottle flies) on our farm. Pretty sure a lot of those flies are coming from the farm down the way. And the they come and multiple on our property. Do you think you method with the fly parasites would work? Just curious and also wondering if a green bottle fly is the same as a regular fly

  2. cary says:

    I don’t know how I missed this post. Must’ve been on vacation. Next summer, definitely. Thank you, Karen.

  3. Jessica says:

    Karen – I shared a link to this post on a local Facebook page (Orangevale, CA) to help someone out with the pesky fly problem they have due to their neighbors chickens.

    Thanks for sharing this tip. I hope it works as well for her as it did/does for you!

  4. Melissa Keyser says:

    Interesting, I’ve never heard of fly parasites.

    We have tons of flies in our coop, but I think they are just normal garbage flies (not that they are less gross….)

  5. Cheryl says:

    I thought I wanted to have a few chickens, but your posts scare me.:)

    Are they worth all of your efforts??

    • Karen says:

      Well, that’s part of the reason I do these posts Cheryl. :) So people can see what it’s really like to own chickens. Not just the “Pinterest version” of owning chickens where they romp through pea gravel and look beautiful. For me, yes they’re worth the effort. I love them. But they’re a responsibility for sure. They’re livestock that needs to be taken care of. Generally they’re easy but issues do come up. But if you want the Pinterest version of chickens … stick to Pinterest. :) ~ karen!

  6. Renee says:

    Penny – I understand your concern. Please don’t worry – they are a sponsored colony, this is allowed in my county, and I am their registered caretaker – they are a TNR colony (trap, neuiter, release) shots, and microchipped. The hang out mostly in my fenced back yard. I got involved in TNR because the cats WERE breeding around here like crazy, and I wanted to do something about it. population has dropped by more than half, and there are NO wandering male cats anymore. So, I am doing a good thing….. I just wondered about using the pwasp for keeping flies out of the food station.

  7. Renee says:

    This sounds great. I feed a small feral cat colony, and I no sooner put their dry food out, in the morning and the flies are all over. Starts again, (if they even leave) when I feed wet food early evening. Would I just sprinkle them in the same area? There is no poop around for them to lay eggs on.

    • Penny says:

      Why (and where) in the world are you feeding feral cats?? Unless they’re all neutered you should know that they WILL breed to take care of all the available food in their territory; including nesting and fledgling birds and small rodents such as voles.

  8. Marti says:

    You had me with that first paragraph. Such lovely descriptive writing.
    Does your mother know you’re using those words?
    Ha. Betty taught you how to spell them, didn’t she?

    Fun blog. Just what I needed today, as it happens!

  9. robert says:

    And just by mentioning Norma watching a diamond you’re suddenly in the same category as 2 other certain very famous blondes, Marie Antoinette as a faux pheasant at the Petit Trianon and Catherine Deneuve talking about her chickens during a fitting at Yves Saint Laurent at the beginning of a documentary about Yves. How in heavens name do you manage such things while talking about poop?!!!!

  10. Cynthia Wehrwein says:

    Hey Karen – I used to get updates and then for some reason stopped getting them and so I signed up again, and I’ve done it a couple of times, but I don’t get signed up.

    • Karen says:

      Hi Cynthia! Hmm. Well I’ve just checked and you’ve successfully signed up this time. Keep an eye on it. You should get an email for my next post Friday! From the look of it you hadn’t successfully signed up before (at least not with this email address). Fingers crossed! ~karen!

  11. Shauna says:

    Don’t even need to read the post – just need to tell you that these things work. We’ve used them since we’ve had chickens and they work great. Now, I’ll go read the post because you may already know that they work:)

  12. Sara says:

    I use a different kind of parasitic wasp (trichogramma I think) through the summer to keep down the wool moth population in my house. Love letting nature do the work. I’m still looking for that backup solution though….any ideas?

  13. janpartist says:

    What is a poop board (sounds technical)?

    • Karen says:

      Hi Jan! A poop board is just a board that goes under where the chickens roost at night. It makes it easy to clean out their coop because you just pick up the board and scrape it all into the compost bin. :) ~ karen!

  14. marilyn says:

    Can I just say I love your writing. You tie things together so well, Glad the flies are out of there.

  15. Snugster says:

    Hey Karen
    What’s the purpose of a poop board?

    • Karen says:

      Hey Snugster! The poop board goes under the roost where the hens sleep at night so when they poop it lands on the board. It makes cleaning the coop easy because you just have to pick up the board and scrape it into the compost bin every couple of days. ~ karen!

  16. Barbie says:

    I wonder if they sell ladybugs? I need to order some for my garden.

  17. Shirley says:

    Who knew??? Your blog is the best thing ever! You make us laugh, you make us cry and you find the most interesting facts to educate us! Don’t ever stop writing!

  18. Lynda says:

    More power to you! I wish I had something for the deer flies that were flying around and around and around and around my head yesterday as I was painting the shed. I tried ignoring them (fail), waving my hands over my head like an idiot (fail – the waving hands part, not the idiot part), spraying them with water (fail). I think they’re even more annoying than blackflies. Why do these bothersome things even exist???

  19. Brenda says:

    Great fly getting rid of trick … here’s mine. If you get a house fly in your house – wait until dark and turn out all your lights and turn on the porch light and open the door – it will fly outside and save you hours of chasing it around inside the house with a rolled up magazine you need to throw out if you do somehow get it. It seriously works.

    • Karen says:

      I did that in reverse at a hotel once. Opened my patio door at night, turned the bedside light on then left the room for dinner. Midway through dinner I screamed and realized what I’d done and ran back to the room which was now thick with bugs. I ended up taking the bedside lamp outside onto the patio and they all eventually followed it outside, lol. It was GROSS. ~ karen!

  20. Miriam Mc Nally says:

    I am so impressed. I don’t have chickens, hens, or bottle flies, but this is brilliant!
    You should get a partnership from the wasp company!
    Nature Vs nature is the way to go!

  21. Lavada says:

    What about plants — basil, rosemary, lemon grass are all planted around my patio area and then a row of lavender. At the back door I have a citronella plant. I rarely see flies when I’m on the patio and not for long if I do see them. And, as an added bonus, never get bitten by mosquitoes. Natural, fragrant, and herbs are useful (and handy) when cooking out.

    • Karen says:

      I’m afraid the only plant that would work in a livestock situation (or any situation where there’s likely to be bottle flies) would be a hedge of Venus Flytraps. ;) ~ karen!

  22. Catherine says:

    I don’t have livestock but I do order ladybirds to have at the aphids. This year with our English ‘summer’ (cold, rain, gloom), the pests are thriving. And this being my first year growing veggies I want to nurture and protect them as much as possible!

  23. Marna says:

    Interesting! I will have to keep the info on hand for what you mentioned and others mentioned too. We have about every type of wasp living near and around our yard, they are awful all summer. Maybe I already have them, we don’t seem to get too many flies, so maybe we do have them. We do have tons of mosquitoes though, thanks for the tip on using a fan. My main problem is they are everywhere all day long now, can’t even do much gardening, and now they say we have the Zika mosquitoes here now. We have several different types including the West Nile and some other one I can’t remember. I need a pet bat. :)

    • Suzanne says:

      Have you tried Picadarin? Best mosquito bite preventer ever. Made from peppers. DON’T get in your eyes! Better than OFF by far. Can be hard to find. I get it from Amazon. Even works on noseeums. Little nasties.

  24. Stephanie says:

    THANK YOU for this post! I’ve been wanting to try these for five years. I’m now convinced after hearing your first-hand actually “doing stuff” report. Thx!

  25. Elaine says:

    You are FAR from an idiot, I can assure you, Karen!! Fascinating reading. I’m more your mother’s age and now live in a condo, therefore, many of your posts don’t fit with my life now but they are so darned interesting and informative plus I’m always amazed at what you research and then actually DO (!!) that I could never give up reading your blog!!

  26. Mark says:

    I had visions of a Bugs Bunny earring when I read how _Norma ripped a half carrot diamond earring out of your earlobe_

    No wonder, I thought, Norma was going for the veg.

    Then I thought, maybe you meant carat…

    (Sorry, couldn’t resist :). )

  27. Melissa says:

    I still have to remind myself not to drink when reading these! Otherwise, it’s a case of “laugh-out-loud-and-out-of-your-nose”. Not pretty, I tell you.

  28. Cynna says:

    We’ve used them for horse barns for years; they help.

  29. Paula says:

    Biological Yes! I am expecting my overnight shipment of nematodes tomorrow because I seem to have a mutant form of flea beetles wreaking havoc on tomatoes (!!! not teeny baby tomato seedlings, but nice, big tomato seedlings), potatoes, and not allowing one single lettuce to survive its infancy this year. Death by nematode! Also, this particular strain is said to love cucumber beetles which must be hatching soon in their evil little underground enclaves. I love this fight by bio stuff! Good luck to you!

    • Karen says:

      I wish that sort of effort would work at my community garden Paula, but with SO many gardens in such a large place it would be useless. :( I do use nematodes for grubs in my lawn though! ~ karen!

      • Mary W says:

        I thought nematodes killed the roots of veggies. In FL I used old fashioned strong smelling marigolds between my tomatoes and veggies to kill the nematodes. What don’t I know about this? In fact the first year of gardening is usually a bust due to nematodes. Help me understand.

        • Karen says:

          Hi Mary W! There are different types of nematodes just like there are different types of bees or butterflies. The type you order online or get at your garden centre for slugs etc. are “beneficial nematodes” that don’t harm grass or vegetables, they just attack grubs (in my case). :) You can read a bit more about them in this post. ~ karen!

  30. Cheryl Smith-Bell says:

    They work great, and I need to order some, myself. You will not need the full summers worth, because they are reproducing/egg laying in the fly larva case, but only one at a time! It is some times hard for them to outproduce the flies, tho, if you have a lot of live stock.

    • Karen says:

      Yes, the guy explained to me that they do reproduce but at such a low rate compared to the flies that they need to be replenished. ~ k!

  31. motherhen says:

    Have you tried the ‘penny in a ziplock bag filled with water hanging in the coop or run’ trick?
    Apparently has something to do with their compound eyes, the water filled bag appears magnified and multiplied and acts like a ‘flyzilla’ to deter them.

    • Karen says:

      No, I haven’t. It’s actually been proven to not work at all, and to just be a coincidence or because of other factors if flies go away when you hang the bags, lol. I have readers that say they work but I couldn’t be bothered with trying out this sort of witchcraft. ;) I was going straight for the scientifically engineered fly killers. Love ’em! ~ karen!

      • Cynthia Jones says:

        I wanna know where they go after they have eaten your flies. Are they waiting somewhere in an underground cave or in your basement until next Spring where they will emerge and eat your brains? Yeh right, they don’t affect humans. Humph! Tell that to the cane toads we imported to kill our cane beetles. Buggers also kill our dogs and scare the bejeebers out of us at night with all their ugly floppin around. You watch out next Spring Karen, I don’t want you going down to the cellar to get that artificial leg and getting swarmed like a scene out of Hitchcock’s “Birds”. And while you’re at it, don’t run with scissors either.

      • Julie says:

        Probably couldn’t find a penny anyway!

  32. MDR says:

    Damm. Anything for mosquitoes?

    • Karen says:

      A fan! A regular fan set out where you’re sitting will get rid of mosquitoes because they can’t fly in even a slight breeze. Most effective mosquito repellant around. ~ karen!

  33. Nancy S says:

    I think it’s douchey. And this was one of the grossest/most fascinating things I’ve read in a long time.

  34. Christy says:

    I did the same by purchasing nematodes to devour the fungus gnat larva that were killing my seedlings. Totally worked…. no pesticide
    Not sure about the 15 year-old girls in Canada, but you have to inject “literally” and “amazing” a few hundred times in New Jersey to capture the essence here..

  35. Nancy W says:

    Oh, and I’m adding those to my order of that coconut husk dirt stuff…

  36. dede says:

    I’m first!!! I’m never first at anything.
    Genius solution. Screw those little buggers. ?

  37. Nancy W says:

    That post went SO well with my dinner. Mmmmm…

  38. Katie Schneider says:

    HOLY SHIT! (do you see what i did there? Maybe it should read holy shit-eaters) This is exactly what i needed! Ordering some now!

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