Hi Richard,

There's a chance that what you are seeing are bird blow flies.

Bird blow flies are common in the nests of many birds, including bluebirds,
> swallows, chickadees, wrens, warblers, flycatchers and raptors.  Research
> shows that heavy infestations can make nestlings anemic (cause reduced red
> blood cell counts) and severe infestations may be lethal (Whitworth &
> Bennett, 1992).  Infestation rates vary from almost 100% in magpies to 50%
> in many bluebirds, to zero in over 100 oriole nests (Whitworth & Bennett,
> 1992).  In most areas, around 5-10% of infested nests are likely to have
> sufficient larval populations to make nestlings sick.  Little is known
> about this parasite since it is rarely encountered in nature, except in
> bird nests.
>
> http://www.birdblowfly.com/generalinfo.html
>

Terry Whitworth, the investigator who put up the website linked above,
invites readers to send data from their observations of bird nests.

If you should disagree with Terry's opinion that it is best to allow blow
flies free access to bird nests because they are "perfectly natural",
http://www.sialis.org/forumlinks.htm offers some advice about controlling
blow flies in bluebird boxes.

-Mike





On Fri, Jun 13, 2014 at 7:48 AM, Richard Tkachuck <rictkal...@gmail.com>
wrote:

> We had a bluebird box with six eggs. Looked in yesterday and saw one dead
> nearly fledged bird and one egg. We assume that the others made it out of
> the nest, but have not seen any around, nor the adults. However, saw about
> eight larvae and two pupae  on the floor of the box.
>
> Can anyone tell what the species might be? Have collected them and are
> waiting for them to hatch.
>
> What I might do to avoid these should they use the box again?
>
> What harm do they cause?
>
> We saw a Red-bellied Woodpecker looking in the box. Would it act as a
> predator?
> Cheers,
> Richard Tkachuck
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