Sevin for Nest Parasite Control
Ken Kostka
Purple Martin Preservation Alliance
Export, PA

    After 20 years of attempting to attract martins to my home in Natrona Heights, PA, I finally succeeded in attracting one breeding pair in 1999, only to be extremely disappointed when the nestlings died of blowfly larvae infestation after reaching only 4-5 days of age. When I told this to Dr. Eugene Morton, an ornithologist and research scientist who has published many scientific papers about Purple Martins in biological journals, and one of the world's foremost experts on Purple Martins, he inquired as to whether I had used Sevin (carbaryl) to control nest parasites. While I did know about the method of total nest replacement for parasite control, I did not know about Sevin, and I was quite surprised to learn that he was a proponent of carbaryl use to control nest parasites in Purple Martin nests.  Dr. Morton, it should be pointed out, does not claim to be an expert on this chemical.

"I used Sevin in my martin colony every year following the first year I had mites kill lots of babies upon hatching.  I started in 1980 and every year since, to 1994. I would sprinkle about 1/4 teaspoon powdered Sevin onto the eggs in all nests at the end of the first week of June, roll the eggs gently to get all the Sevin into the nest and off them.  If there were no eggs in the nest, then I just massaged it into the nest bottom.  Never any problem.  I mean I monitored all adults and nestlings and never any problem. Young fledged at normal weights, adults returned faithfully in future years. Furthermore, my adults all lived very long lives indeed, my oldest more than ten years and my young were found dispersed as breeders to other colonies.  I was definitely a "source" not a "sink" for the Maryland martin population. THERE IS NOT THE SLIGHTEST DOUBT THAT SEVIN SAVED 100'S OF YOUNG FROM MITE DEATH AND THAT THERE WAS NO SHORT OR LONG TERM PROBLEM WITH ITS USE ON THE MARTINS. [editor's note: emphasis mine] I don't know the literature on Sevin only my own monitoring of my use of it on my martins over many years.  I can show no effect on hatching success, fledging success, adult longevity, clutch size, and that's enough for me to state that Sevin, as purchased in a local garden shop for use on vegetables and as a "flea powder" on cats and dogs is safe and effective and very time saving for landlords."  -Dr. Eugene Morton

Examples of blowfly-related nestling mortality.

    When I spoke to other landlords about my experience, I learned that quite a few others had also apparently lost nestlings to blowfly infestation. In many cases, the nestlings were only 4-5 days old.  While there was no conclusive proof that the deaths were caused by blowfly parasitism rather than disease, poisoning, bad weather, or parental neglect, none of these latter causes appeared to be to blame since the parents seemed to bring plenty of food, were attentive, and the weather was good, although hot and humid. The dead nestlings were discovered during their first post-hatching nest check, suggesting that nest checks at very small (one or two pair) colony sites should be done sooner and more often, perhaps every other day after hatching, if the landlord wants to guard against this occurrence. Vigilance is the key, especially with SY parents, that are inexperienced breeders and tend to be poorer parents!

The following is a list of landlords who seemingly lost nestlings to blowfly larvae. In all but one case, this was the landlords' ONLY nesting pair, and in all but two cases the nestlings were less than one week old:

Emmanual Erb, Rundell, PA. July 1999. Nestlings found dead at 5-6 days old. Nest was infested with blowfly larvae. One was still attached to the remaining dead baby. Other nestlings gone. Parents: ASY-M, SY-F. Parents hung around for at least one day after nestling deaths. Cavity type: wooden T-14 compartment. Blowfly larvae were concentrated in nestbowl area. When dead nestling was removed, many blowfly were right underneath.

Albert Erb Jr., Holmes Co., OH. July 1999.  Nestlings dead at about 6 days old. Nest was infested with blowfly larvae. Parents both ASY. This was a second nesting attempt.  The first attempt also ended in failure when the nestlings were 11-12 days old, and that nest, too, was infested with blowfly larvae. (The nest cavity was cleaned out between nesting attempts.)

Ron Warden, Springboro, PA. mid 1990's. Nestlings dead at about 9 days old. Nest was infested with blowfly larvae. Cavity type: wooden T-14 compartment.

George Duncan, Prospect, PA. mid 1980's. Nestlings dead at 5-7 days old. Nest was infested with blowfly larvae.

Noah Yoder, Belleville, PA. 1999. Three of five nests lost to mite or blowfly larvae infestation. "There were bugs and worms in the nests."  He had used Sevin the year before and had  no problems.

Ken Kostka, Natrona Heights, PA. 1999. Nestlings dead at 4-5 days old. Nestbowl infested with at least several dozen blowfly larvae. No pupariums found, but many blowfly larvae were full size (1/4 inch) Also 4-5 blowfly on each of the 2 dead nestlings, mostly in ear and eye sockets. Parents attended for 1-2 days after nestlings were dead. Parents both SY. This was a renesting attempt. First set of eggs disappeared. Cavity was 13 inch natural gourd. Many dead oak leaves, twigs, dried green leaves.

Milo Miller, Smicksburg, PA 2004. Nestlings dead at 12-14 days old. Nest infested with blowfly larvea.

There are ornithologists who do not believe that blowfly larvae will kill nestlings, but my observations and experience has led me to conclude otherwise. I have also seen nestlings die from hypothermia (seemingly) as a result of poorly done nest replacements, although I do believe that total nest replacements are a good management practice.

Some landlords spray a 5% liquid Sevin solution on the floor and lower walls of the nest cavity (and nest tray) prior to the birds arrival then allow it to dry for at least several days, after which they place nesting material (cedar shavings or soft, dried pine needles) inside the cavity and nest tray. This nesting material covers the sprayed areas. Some landlords place a half teaspoon of powdered 5% Sevin under the nestbowl after hatching or on the floor of the cavity during the first nest replacement. It can be gently spread around with a small paintbrush then covered with clean nesting material.

Large numbers of blowfly larvae will not always be seen by just looking at the nest. You must check under the nestlings in the bottom of the nestbowl, because this is where blowfly larvae will hide during the day. The larvae crawl up out of the nestbowl at night and attach themselves to the nestlings to suck their blood.   Adult blowfly larvae will not be killed by Sevin, so they should be removed if they are found. If the nestlings are less than 10 days old, be careful to maintain the integrity of the nestbowl when doing a nestcheck or nest replacement (keep the center of the nest bowl-shaped) so that the nestlings all stay huddled together. This allows the female to cover the nestlings and keep them warm. Nestlings cannot maintain their own body temperature until they are about 10 days old. Usually, just the bottom of the nestbowl itself is infested with the blowfly, so replacing just the material in the center of the nestbowl (and not all of the coarse, bulky nesting material surrounding it) will suffice in ridding the nest of blowfly larvea and eggs.

I do not necessarily wish to imply that I (or the PMPA) advocate Sevin use as a management practice.  In fact, if one vigilantly monitors that first nesting pair or two, then nest replacements can eliminate the blowfly problem. But one needs to be VERY careful about doing a nest replacement with nestlings that are less than 10 days old. Although nest replacements are not recommended for nests with young that are less than 10 days old, in cases of early infestation, doing one can mean the difference between life and death. However, special care must be taken in replacing the nests of very young nestlings (i.e., nestlings 1-8 days old). It is especially important to form a good artificial nestbowl or depression in the bed of replacement nest material and line it with green leaves of any type. This leaf-lined bowl insures that the nestlings will stay in a tight huddle so the female can cover and brood them properly. The majority of the nest parasites are usually concentrated in this nestbowl area, so you may wish to scoop out and replace just the nestbowl material itself rather than replacing the entire nest. In either case, it's a good idea to monitor such nests closely, perhaps checking them every couple of days.