If you would like help determining if your nests are infested, consider sending them to me. I have a U.S. Fish & Wildlife permit which allows me to examine bird nests from anywhere in the U.S.
Bird blow flies can be very hard to identify to species, and we prefer to have both pupae (or empty pupal cases) and adults, if possible. The best way to ensure your sample will include adult flies is to collect the nest within 7 days after young fledge, before adult flies have emerged. I like to use 1-gallon Ziploc® bags and put each nest in a separate bag. Write only the nest number on the bag and give me a separate sheet with other data. Please refer to Nest Donation Report Form. Please include bird species, state, county and the nearest town where the nest was collected; also include your address and e-mail, so I can contact you. Small arthropods like mites and fleas will crawl from poorly sealed bags, so make sure they are closed tightly. If there are lots of bugs, put the individual bags in a big garbage bag, seal it also. If you decide to include a note in each bag, write in pencil or waterproof ink or data may be lost in a wet bag. Please do not disturb a nest with young, wait until they fledge.
Do not put the bag in the freezer, since this will kill larvae and pupae. Keep bags you are saving to send in a cool, dry location, out of the sun. I am interested in any nests you find, even if nestlings have long since fledged, because pupal cases will remain in infested nests and I can ID them. Nests that failed early will not be parasitized, so please don't send those.
If you keep the bags for awhile to send several at once, adult flies will emerge in the bag. You will hear them buzzing, but don't worry as long as they can't escape. When shipping bags in boxes, don't worry about padding nests when you send them. The nests provide their own padding. If you mail them in an envelope it should be padded or it may be run through a canceling machine. Usually the U.S. Postal service is the cheapest way to send nests.