A Bluebird Box Surprise

With a new bluebird season approaching I decided to inspect each of my houses to see if they were in need of cleaning and/or repairs. While doing so I came across the tubes of an organ-pipe mud-dauber that had been built inside one of the boxes. Its grip on the inside wall had apparently weakened causing it to fall upon the aged bluebird nest that had been there since the previous season. This steely-blue solitary wasp is docile and doesn’t sting unless you decide to grab one and aren’t aggressive as the social paper wasps which will attack and sting with even the slightest provocation. The female wasp will build its nest anywhere that’s out of the weather- on the eaves of houses, under awnings, inside garages, and even, as in this case, in bird housing. She finds a damp area of soil and digs into it with her jaws rolling it into a tiny ball about the size of a BB. She then takes this ball and with the skill of a trained mason painstakingly forms each cylindrical tube row by tedious row until the tube is complete. The differences in color in areas of the tubes show that mud was collected from different sites. Below is a photo of a female that was building a tube on my front porch several years ago.

Once a tube is complete she then begins capturing unwary spiders and stings them injecting her paralyzing venom which keeps them alive, but immobilized. She lays a single fertilized egg in the cell with the paralyzed spiders, seals it up with mud and then goes about the same task of provisioning the other cells. (Go here to check out a prior post that shows photos of spiders removed from a mud-dauber tube. Note the larva in one of the photos feeding on one of the spiders.)The male’s role is to stand guard at the nest preventing the theft of the stored prey by intruders including other mud daubers. Days later the eggs hatch and the developing larvae feed on the collected spiders. Once fully grown the larva then spins a cocoon about itself, which is white in color and then turns dark and rigid as seen in the photos.

Here they’ll remain until fully developed when they then emerge as wasps, eating their way out of the cocoon and the tube. Note the exit holes where two developed wasps escaped. This was a cluster of 5 connected tubes revealing a total of 16 cells, some containing what appeared to be 5 viable cocoons that have yet to hatch. There were some empty cells, which exhibited no exit holes. As noted before the tubes had fallen off of the inside wall of the box which exposed the cells and allowed entry to them. Bluebirds, or any other bird for that matter, entering the house would’ve feasted on any wasp larvae and/or provisioned spiders in them.