Skip to Left navigation Skip to Main content Skip to Footer

University of Minnesota Extension

Species guide - species detail

Back to Species guide categories | Back to Wasps

Psenulus sp.



Psenulus is a genus of solitary wasps in the family Crabronidae. They are known for their large, blocky heads. Although there are around 160 species of Psenulus, only 6 species are found in the Midwest. The greatest species diversity can be found in Indomalayan Realm. A recent phylogenetic analysis provided strong evidence that this genus is the closest living relative to bees. The specimens of Psenulus collected from the Minnesota Bee Atlas bee blocks were missing many anatomical details that could help with identification. Therefore, these specimens were not able to be identified to species.


Psenulus wasps are relatively small, usually with a length of 5mm-7mm. They can range in color from totally black, or black with amber, brown, or yellow body parts. The pronotal lobes of Psenulus species are always dark-colored. One way to immediately identify a suspected Psenulus wasp is by the presence of an extremely boxy square head with large eyes. Wasps in the genus Psenulus can be distinguished from other closely related Crabronids due to the presence of a large, highly raised vertical carina that spans across the front of their faces. Also, the hypostomal and occipital carinas merge on the underside of the head.

Nest Structure

Psenulus wasps nest either in hollow stems or straws. They are known to nest in the stems in bramble, reeds, currant bushes, and roses. However, these wasps also utilize abandoned holes in wood made by Coleoptera or Hymenoptera. This is why they are found in our bee blocks. The nests of Psenulus species are unique because they are lined with silk, and silk is also used to make the walls between the cells. While many insects make silk when they are young, it is rare for them to keep making it as adults. In the case of Psenulus, only the female insects make silk. The source of the silk in Psenulus nests was a mystery for a long time until it was discovered that it comes from bristle-like spinnerets on the hind edges of the fourth and fifth segments of the abdomen.

Hole Sizes

No information at this time.


In Minnesota, Psenulus species are usually bivoltine, but some species can also be multivoltine.

Activity Period

Psenulus wasps are usually active in Minnesota from June to August.


Gittins, A. R. 1969. Revision of the Nearctic Psenini (Hymenoptera: Sphecidae) I. Redescriptions and keys to the genera and subgenera. Trans. Am. Entomol. Soc. 95(1): 49-76. Peters R. S., Krogmann L., Mayer C., Donath A., Gunkel S., Meusemann K., et al. 2017. Evolutionary history of the Hymenoptera. Curr Biol. 27(7):1013-1018. Trypoxylon atratus FABRICIUS 1804; Psenulus brevitarsis MERISUO 1937; Psen chevrieri TOURNIER 1899; Psen haemorrhoidalis COSTA 1871; Psen minutus TOURNIER 1899; Psen montanus COSTA 1861; Psen nigricornis TOURNIER 1899; Psen pygmaeus TOURNIER 1899; Psenulus rubicola HARTTIG 1931. 2024. Psenulus pallipes (Panzer, 1798). Available at: Accessed February 26, 2024

Minnesota Record Map

These data are from the Minnesota Bee Atlas project.

Back to Bee species guide