The Amateur Anthecologist: Sceliphron caementarium

Sceliphron caementarium ♀ perched on an unused beehive bottom board.

While going through empty honeybee hives I often find signs of other insects taking up residence within. The usual suspects are lesser wax moth larvae (Achroia grisella) and European earwigs (Forficula auricularia). On occasion, I have discovered small clay nests such as in the photos below and just yesterday I discovered the culprit. The black and yellow mud dauber, or Sceliphron caementarium, is a large yet docile solitary wasp in the Sphecidae or thread-waisted wasp family. This isn't the first time I've found wasps inside unused beekeeping equipment, I occasionally come across a nests of semi-social wasps Polistes aurifer and P. dominula. None of these species are of consequence to honeybees, and the paper wasps are probably beneficial to an apiary since there is a high likelihood they will prey on wax moth larvae which, unchecked, will destroy unused wax comb. Sceliphron caementarium, however, hunts spiders to provision its nest while the adults feed on nectar.

Sceliphron caementarium nest

Nests of the black and yellow mud dauber are composed entirely of mud, so this species is highly dependent on a nearby water source. Adult females find a muddy area to alight, then make a pea sized ball of bud with their front legs and mandibles before carrying it to a sheltered location to build. Empty bee boxes provide the perfect shelter as there is a small entrance protecting the nests from attack from mammals or other large predators. The species is found in nearly every state in the US, Mexico, Southern Canada, and even South America and Eurasia (among many exotic countries) as an invasive species. It is interesting to compare the colors of the nests as they represent different types of mineral constituents found in different regions.

Nearly completed mud nest on old honeybee comb.

As mentioned above, the adult females hunt spiders to provision their nests, but they don't kill them. Their powerful sting immobilizes the spider to keep it from harming the larvae or pupae while in the nest but keeps it alive so it doesn't go bad, fresh meat in other words. The wasp lays her egg on the first spider she packs in the nest, then continues to place up to 25 or even more spiders in the cell. Their favorite prey are often orb weavers (Araneidae), lynx spiders (Oxyopidae), crab spiders (Thomisidae), jumping spiders (Salticidae), and sac spiders (Anyphaenidae), though they seem to have a preference for spiders that build webs. The most fascinating evidence suggests that individuals have different preferences in the types of spiders they like to paralyze for their nests, even when in the same region.

Completed mud nests on old honeybee comb.

After provisioning and covering each cell entrance, the entire nest is coated in a thick layer of mud to protect the brood from parasites and perhaps also to moderate the temperate conditions inside. While the wasps themselves are docile and do not defend their nests, they are considered to be aesthetic pests due to their nests being perceived as unsightly, especially when attached to buildings and other man-made structures. There is even the possibility that fatal plane crashes have been the result of an unfortunate nest location.

Sceliphron caementarium pupal case

Inside the nest, at this time, pupal cases were present with larvae in the prepupal stage. There were few spiders present, though at one time earlier in the year the cells were likely full of spiders. The larvae, in preparation for pupation, devour first all the spider hemolymph (blood), then the spider carcasses in their entirety. The pupal case is very thin and malleable, made from what seems to be some sort of secreted resin, and held in place by thin strands. I speculate the case may be suspended from the walls to prevent excessive heat or cold from conducting through the mud and harming the pupae.

Sceliphron caementarium ♀ with the characteristic and very elongated pedicel (waist).

Although these are large wasps which surely evoke fear in the hearts and minds of the uninitiated, they are certainly not prepared biologically for defense and would be more likely to flee than sting. Unlike the social wasps, they do not spend the night in their nests but rather sleep in thickets of woody debris or other secluded locations (such as an empty beehive). As a result, or by circumstance, they do not aggressively defend their nests as in genera Dolichovespula, Vespula, Polistes, and a few others. Also unlike the social wasps and bees which sting as a form of defense, the venom of Sceliphron caementarium is solely formulated for the paralysis of spiders and lacks many of the pain-inducing compounds found in them. The quantity of venom is also significantly reduced. For instance, the European hornet (Vespa crabro) is estimated to have ten times the venom compared to S. caementarium. Stings by the black and yellow mud dauber, apparently, are most likely the result of rough handling.

Sceliphron caementarium ♀

While the larvae feed on living yet immobilized spiders, adults feed on nectar. Like many wasps they do not have very long probosces so they are most often found on flowers with easily accessible nectar, such as plants in the Apiaceae, or carrot family. While they do not intentionally collect or eat pollen, it is inevitable to contribute to pollination when visiting many flowers of the same species.

Sceliphron caementarium ♀

The Amateur Anthecologist

Saturday, August 13, 2016

Sceliphron caementarium

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