My efforts for blowfly larvae control in nests have been successful, until quite recently.  This set of larvae were so strong and in large numbers, the nestlings became too anemic and weak to survive the amount of feedings they were ingesting from Mom and Pop Blue.  They were 9 days old when death came knocking at their nestbox door.  The last time I lost a whole brood to blowflies was Spring 2008.   Not all happenings on the bluebird trail are happy ones.   I will continue my two methods of control:   (1) hardware cloth bases below nesting material (helpful but not as effective as the only method of control) and (2)  the use of puffing some organic food-grade Diatomaceous Earth inside the center of the nesting material and underneath the nest on the wood floor of the nestbox before bluebird eggs hatch. The key is to eradicate the larvae while very young, right after they hatch, which nature usually times around the same time the birds’ eggs hatch. I had treated this nestbox with the DE, like I have all others.  This year and at this nestbox, I must not have applied the right amount of the DE to take care of the number of hatched larvae to cause the damage they did.  Below are a set of photos of different methods I’ve used  in past and presently (applying DE) and another method of using leftover hardware cloth from making the Noel Guards for my boxes for the bases to slide underneath completed nests.  Captions will explain the pictures.  Warning:  The last photo in this series is not a pleasant one.  I cropped out the dead bluebirds, but I wanted you to see the larvae that killed this brood.  You will note how large the larvae got, some gorged with blood, and a dead bumblebee–which obviously was the last-ditch effort of feeding the parent birds attempted to make for their 8-day old kids, too weak to eat.  This is a good representation photo of what the larvae looks like when healthy and successful feeding on the nestlings at night.   I had to dissect the pine needle nest to find this big patch of them.

I put a clean washcloth on top of nest with eggs. I use a mustard/ketchup type squeeze container with tip and insert a few puffs in three sections inside the center of the nest. THIS IS DONE BEFORE HATCHING.

I then repeat a few puffs underneath the nest material on the bare wood floor. I use the metal paint scraper to gently lift the nest up to apply. Note the clean washcloth remains on top of nest. This keeps any DE powder off the top of the nest.

I keep the box open for a minute to let any DE powder settle. Before I remove the washcloth, I use a clean paintbrush to remove any powder residue from the sides of the nestbox. THEN I peel back towards me and out the washcloth, close and secure the box, and quickly leave the nestbox area.

I’m making bases made of leftover hardware cloth from the construction of the Noel entry-hole guards. I use tin snippers to cut and shape to fit the inside of a nestbox. These are slid in an already completed nest. If this can be done after nestcup is completed but before eggs are laid, that’s ideal. If not, you can slide it in after the eggs are laid, but be gentle!

I’m experimenting with one-half inch off the nestbox floor AND one inch off the nestbox floor. This pictures shows a tad higher than one-half inch.

This is about one inch off the nestbox floor. I am finding I like this much better. I can always remove some of the nesting material if it brings the nest up too high close to the entry hole. Also it allows easy brushing out of blowfly larvae when it’s an inch off the floor.

Here is an active bluebird nest with the one-inch high base. I slid this in a nest with eggs. I also applied a thin layer of DE to the bottom of the box. Look closely; you can see the eggs! This box fledged baby bluebirds.

You’ll note dead bumblebee–brought in by the parents but not eaten by the nestlilngs. Larvae are plump, some gorged with blood. This larvae killed 8 and 9 day old bluebird nestlings.


  1. Having lost my first bluebird brood (5 chicks) to blowfly larvae, I am interested in your success with D.E. Where do I get organic, food grade D.E.? For years we have had innumerable broods of bluebirds and tree swallows in boxes. This is our first experience with blowflies, not a happy one since we only had one nest of bluebirds this year. Should I remove the nest with dead chicks and clean out the box, hoping for another brood.? It is still early, especially for Vermont. Last year we had a second brood in one box in mid July. Thanks for any advice you can give me.


    • Apologies…this is the first I’ve seen of your inquiry posted on May 27th. Go to your Search Engine and Google “organic food-grade Diatomaceous Earth”. There are several organic companies that sell it. Some garden centers might have it in smaller quantities. You do NOT want the commercial chemically added diatomaceous earth used for pools and spas. Here is a good place to start by getting a 2-pound size bag (lasts and lasts) and the pest pistol and had it shipped to me. You can also buy yourself a plastic refillable mustard or ketchup dispenser–the kind that has the tip and cap for about one dollar at grocery stores in the kitchen utensils section or at Wal-Mart. I ordered my DE and a “pest-pistol” which is small and works great for fast, efficient puffing of the dust in the center of the nests during egg laying or after the egg clutch h as been completed. I do it very carefully by putting a clean terry-cloth washcloth over the nest and puffing the DE in small puffs throughout different sections of the nest and at the bottom of the nest by the floor so that when the larvae settle down inside the nest during the day, they can’t breathe in the DE dust and die off. Not ALL of the larvae will die as some escape the dust but most do. It keeps them at bay. You do not want to OVER-PUFF this stuff and make sure it’s UNDER the nest cup by some and not too close to the nest cup. It does take some practice. I actually have a two-page writeup with photos of how I do this quickly and safely for the adults birds and the baby birds. When I use DE, I never have nestling deaths anymore and have successful fledging success. I’m so used to doing it now, it’s like old hat for me. I am also starting to use hardware cloth risers to fit the floors of nestboxes to supply for circulation under the nesting boxes. I’m experimenting not using DE in those boxes to see if I can control the larvae. I have had consisten larvae issues since I started the bluebird trail, so fighting these parasites in nests is my number one issue regarding insect control in nesting boxes–my number two is wasp species. If you’d like for me to send the Word document (two pages) to you on Email (I have your Email address–it’s private to me only as the page administrator), I’m happy to Email it to you. I may post it online here soon. The use of DE in my nesting boxes has taken much stress off of me in caring for these boxes on the trail. I’ve had nestling deaths from the larvae–it’s a terrible experience. ALWAYS remove used and soiled nests after each fledging in nesting boxes. If a bluebird or another native species puts their own nesting materials over the old, there can still be parasites in the old nest, even if those young fledged–such as blowfly larvae that survive the first brood, mites, earwigs …. and others. Here is where I purchased a 2-pound bag of DE and the pest pistol: You can also go to another great site on this organic food-grade DE: Wolf Creek I think it’s better to just go online, but I know Harry Schmeider, Ambassador for the Bluebirds, has found it in some stores in his area in PA. Here is Harry’s site on blowfly larvae: Hope all this helps. Somehow, I never received original notice from this website you left an inquiry. Glad you wrote back–I got that notice and was able to search where you left your first inquiry. I usually don’t have problems with this from WordPress. Good Luck!


  2. Hello- I am a backyard Bluebird Monitor in Central Virginia and lost four 9-day-old BB chicks in 2010 due to blowfly. I asked local BB folks, tried a recommended systemic tick spray in empty boxes and in nest before eggs were laid, with little success, yet fledged five nestlings this year in two cycles. I want to share my nesting material story…

    I have a new suggestion for monitors: I read that pine needles seem to be the ideal material for blowfly, so when I discoverd them in the first pine needle nest, I destroyed it (burned it) and built another from the cocoa lining found in planter boxes and hanging baskets. This I did when nestlings were nine days old. Neither Mama or chicks minded the switch. The next day I noticed that the chicks were getting their nails hung up in the cocoa, so I took a bunch of raffia (found in crafts stores), cut it into 2 inch strips, and lined the nest over the cocoa. The nestlings liked this and successfully fledged. They actually had more room in the box during especially hot days. I found no blowfly larva in the cocoa material. It is spotless. This cocoa material is cheap and can be found in any garden center. Try it.

    Good luck with your season. Diane


    • Hello, Diane. Thank you for sharing here. I do not use any pesticide-type sprays in any of my nestboxes. The blowfly lays eggs in birds’ nests, and the bluebird gets hit hard by these in nestboxes, in certain areas. I have this issue chronically in just about every brood. This year, the blowflies arrived later than usual and laid eggs in nests later than usual. My first two broods this year were much lighter in larvae. However, third broods are particularly strong this year on my trail. The organic food-grade diatomaceous earth never touches the birds the way I apply it. It is a safe solution for a trail as I’m limited in natural clean-nest material made by bluebirds. I do save clean, unused nests (such as when a female is killed and thus the nest is abandoned or the eggs go missing). I used to do nest switch outs early on, particularly when I only had one nestbox. I have plenty of clean, natural white pine mulch on my own grounds, so I can also create pine needle nests from that. I do not buy manmade materials to use for nest switch outs–do not have to. I appreciate you sharing what you have on the availability of this in emergencies and am glad it helped you during your situation. That is good to know! I have a blowfly problem in ALL nests, not just soft or coarse grasses or a mix of pine needles and grasses or just pure pine needles. As a matter of face, the brood of 4 I just lost, in spite of effort for blowfly deterrence and treatment, was all pine needles–I took photos of the amount of blowfly and many gorged with the nestlings’ blood from the night before. I did post that picture on a recent post. However, since I treat all my nests, needles or grass, with the DE, that is my biggest treatment that works for me year and after year. ONLY this year, have I seen a stronger, more robust set of blowfly larvae surviving my treatment. Since, 2008, I’ve lost ONLY one brood to the larvae since my treatment program–and that was recent (this season in July 2012). I can attest that some very tight grass nests were packed with dead blowfly larvae from my treatment upon cleaning out a nest that fledged baby bluebirds, so both grass and pine needle nests are hit by larvae (at least for me). The blowfly female looks to lay her eggs in a birds nest in general–those blowfly larvae hatch on or around the same time as the birds eggs hatch. I have now found it is important that I treat all nests right away, on or around the time the female creates her cup and as soon as egg laying begins. I find the DE is even more powerful in eradicating the larvae after they hatch and while still very small. You are correct–the bluebirds are quite tolerant of us intervening. Isn’t that a wonderful thing, too! I’m not sure about cocoa mulch. One reason why I shun it is I know it can be toxic to pets if they eat it, so I would be one probably not to try it. We monitors care so much and do what we can to help the bluebirds succeed in fledging their babies. Thanks again for sharing what has worked for you.


      • Cocoa MULCH is not what I used. The cocoa or coir is a hemp-like material used as the liners for hanging planters. Sorry for your BB loss. Not convinced about DE, and will be more vigilant about monitoring and burn infested nests and create new. Check out my blog to see the actual nest material I used.


Thanks for your comment. Since I review and approve all public comments before publishing, give me a few days to respond to your comments and inquiries. Thank you.

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.