‘Was that a wasp with the headless body of a bee impaled on its sting?’ I asked myself a few days ago as I sat beside a planted tree disc covered in dense small periwinkle. The insect, about four centimetres long, flitted and scrambled nimbly through the greenery. Curious, I took several photographs. They clearly show its black body, yellow markings, and long legs. Particularly striking is the thin stalk, which I initially mistook for a sting. It sits at the thickened part of the abdomen. It was not, therefore, an impaled bee, but the American Mortar Wasp.
Presumably, it was searching for spiders. That is how I initially interpreted its movements. Whether it was actually hunting at that moment cannot be determined from my photographs alone. I found it fascinating to watch it foraging through the periwinkle.
The American Mortar Wasp. Source: own photo
Sceliphron caementarium, also known as the American Mud Dauber, belongs to the family Sphecidae, classified as a type of mud dauber wasp. Its body is black with yellow markings. The long petiole (abdominal stalk) is usually black as well. Females reach a body length of about 24 to 28 millimetres, while males remain slightly smaller. (Source: Wikipedia)
The close-up photographs allow for a detailed examination of this body structure. The long legs reach between the leaves, the brownish wings rest over the back, and the connection to the rear body segment appears almost thread-like. These are the kinds of details I can observe longer in a photograph than is possible when watching a moving animal.
The American Mortar Wasp. Source: own photo
Paralysed Spiders as Food for the Brood
My suspicion about the spider hunt fits this wasp’s lifestyle. The female catches spiders, paralyses them with a sting, and carries them into her brood cells. There, they serve as food for the larvae. The adult American Mortar Wasp feeds on, among other things, flower nectar. (Source: University of Florida)
There are even individual differences in prey selection. Some females specialise heavily in certain spider species, while others utilise a broader spectrum. I find it particularly interesting that different hunting habits can be observed within the same species. Which prey the wasp in my photographs might have been seeking remains open.
The American Mortar Wasp, likely searching for spiders.
Source: own photo
Brood Cells Made of Mud
The name ‘Mortar Wasp’ describes its building method. The female collects damp mud, for example from the edge of puddles, and forms it into individual brood cells. Suitable locations are sheltered spots, such as on buildings or under rock ledges.
Each cell contains a supply of several paralysed spiders and one egg. Once fully provisioned, the female seals the opening with mud. Several such chambers form a nest, which can additionally be coated with a layer of mud. (Sources: BugGuide, Iowa State University)
Thus, its life involves alternating between very different activities: collecting building material, forming a cell, hunting spiders, and caring for offspring. This gives me an idea of what might lie behind the flying and scrambling I observed.
Habitat
The American Mortar Wasp originally comes from North America and has also been introduced to Europe. Meanwhile, it is also found in Switzerland. The Swiss Entomological Society describes its nesting sites as including structures near bodies of water. (Source: SCNAT)
It lives solitarily: the female builds and provisions her own nest. The species is considered non-aggressive towards humans; stings are rare. Even where several nests are located close together, they are built by individual females.
From my first encounter, I am left with the photographs and a first glimpse into the life of this fascinating wasp. Its unusual body structure has made me curious. During my next observation, I want to pay attention to whether it is carrying a spider or a small lump of mud. Based on what I now know about it, I would already recognise something more of its daily routine in that.
Until next time,
Helga
Have you ever seen this species of wasp? Then I definitely want to know more.