smiling mason wasp

(Ancistrocerus campestris)

Conservation Status
smiling mason wasp
Photo by Maureen Burkle
  IUCN Red List

not listed


not listed


not listed


Smiling mason wasp is a small stinging wasp. It occurs in the United States east of the Great Plains and in southern Ontario Canada. In Minnesota it is restricted to the southeast quarter of the state, where it reaches the northwest extent of its range.

Adults are small and black with yellow markings. The front part of the body (mesosoma) is connected to the rear part (metasoma) by a narrow waist (petiole).

The female has a to 716 (9.0 to 11.0 mm) forewing length.

The head is black. There are two large compound eyes, one on each side of the head, and three small simple eyes (ocelli) in a triangular pattern at the top of the head between the compound eyes. The inner margin of each compound eye is notched. The antennae are thread-like and have 13 segments, including a long first segment (scape) at the base, a short second segment (pedicel), and a whip-like section (flagellum) with 11 segments (flagellomeres). The upper side of all antennal segments is black. The underside of the scape is yellow. The underside of each flagellum is yellowish-brown. The last flagellum is not hooked at the tip. The jaws (mandibles) are long and knife-like. The plate on the face (clypeus) is yellow with a black spot in the middle. The spot usually has a narrow black stripe that connects it to the upper margin of the clypeus. There is a yellow spot on the head between the antennae bases, and a small yellow spot (postocular spot) behind each compound eye.

The thorax is black and has three segments, the prothorax, mesothorax, and metathorax. However, the first segment of the abdomen (propodeum) is fused to the thorax, giving the thorax the appearance of having four segments. The upper plate on the prothorax (pronotum) is short and collar-like. It does not have a narrow transverse ridge (carina). It extends rearward on the sides to the plate at the base of each wing (tegula). It appears horseshoe-shaped when viewed from above, triangular when viewed from the side. It is mostly black except for a yellow band on the front margin of the upper (dorsal) surface. The band is widest at the sides, narrowing to the middle, and is sometimes narrowly interrupted in the middle. On the mesothorax, the large front plate (mesoscutum or scutum) is entirely black, with no yellow markings. The smaller rear plate (scutellum) has a pair of rectangular yellow spots. The spots are small and widely spaced, at least as far apart as the width of one spot. On the upper surface of the metathorax (metanotum) there is a horizontal, slightly curved, yellow line. The spots on the scutellum and the line on the metanotum together have the appearance of a smiley face. This is the feature that gives the wasp its common name. There is a yellow spot at the base of each forewing and a larger yellow spot on the side of the thorax below the wing bases. The first and second abdominal segments form a petiole that connect the abdomen to the thorax.

The first segment of the metasoma is wider than long and only half as long as the second segment. It is black with a yellow band at the rear and a yellow spot on each side. The band is widest in the middle, and the spots on the side sometimes merge with the band. The second segment has a broad yellow band at the rear and is larger than the remaining segments combined. The third segment has a narrow band at the rear. The remaining segments are entirely black.

The wings are smoky brown with dark veins. They are folded longitudinally over the body when at rest. On the forewing, the first discoidal cell is very long, about half the total length of the wing. There are three submarginal cells.

The legs are black. The first segment (trochanter) is not divided – it has just one segment. The fourth segment (tibia) of the middle leg has a single spur at the tip. The last part of each leg (tarsus), corresponding to the foot, has five segments. There is a pair of claws at the tip of each tarsus. The claws are split (cleft) at the end.

The male is smaller, with a ¼ to (6.5 to 9.0 mm) forewing length. The antennae have just 12 segments. The last flagellum is hooked at the tip. The spot between the antennae bases is smaller. The clypeus is entirely yellow, with no black spot. The postocular spot is sometimes very small. The band on the metanotum is often very narrowly interrupted in the middle. The abdomen has seven visible segments.




Female forewing length: to 716 (9.0 to 11.0 mm)

Male forewing length: ¼ to (6.5 to 9.0 mm)


Similar Species










The wings are folded longitudinally over the body when at rest.


Life Cycle


The female nests in a preexisting cavity: in a boring in wood, in sumac stems, and in old mud dauber nests. Within the cavity she creates a partition with mud, provisions it with a paralyzed caterpillar, lays a single egg, and seals the partition with a mud plug.


Larva Food


Twirler moths (Family Gelechiidae) and flat-bodied moths (Family Depressariidae) caterpillars


Adult Food




Distribution Map



24, 27, 29, 30, 82, 83.







Hymenoptera (ants, bees, wasps, and sawflies)  


Apocrita (narrow-waisted wasps, ants, and bees)  
  No Rank Aculeata (ants, bees, and stinging wasps)  


Vespoidea (vespoid wasps)  


Vespidae (hornets, paper wasps, potter wasps, and allies)



Eumeninae (potter and mason wasps)  







Common Names


smiling mason wasp












On insects, a hardened plate on the face above the upper lip (labrum).



A segment of the whip-like third section of an insect antenna (flagellum).



In Hymenoptera: the front part of the body, consisting of all three segments of the thorax and the first segment of the abdomen, to which the wings are attached.



In Hymenoptera: the armored rear part of the body, consisting of the second segment of the abdomen and all segments posterior to it.



On plants: the stalk of a single flower in a cluster of flowers. On insects: the second segment of the antennae. On Hymenoptera and Araneae: the narrow stalk connecting the thorax to the abdomen: the preferred term is petiole.



On plants: The stalk of a leaf blade or a compound leaf that attaches it to the stem. On ants and wasps: The constricted first one or two segments of the rear part of the body.



The exoskeletal plate on the upper side of the first segment of the thorax of an insect.



On plants: An erect, leafless stalk growing from the rootstock and supporting a flower or a flower cluster. On insects: The basal segment of the antenna.



On insects, the last two to five subdivisions of the leg, attached to the tibia; the foot. On spiders, the last segment of the leg. Plural: tarsi.



A small, hardened, plate, scale, or flap-like structure that overlaps the base of the forewing of insects in the orders Lepidoptera, Hymenoptera, Diptera, and Homoptera. Plural: tegulae.



The fourth segment of an insect leg, after the femur and before the tarsus (foot). The fifth segment of a spider leg or palp.





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Maureen Burkle

    smiling mason wasp      








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Other Videos
  Mason Wasp Unsuccessful in Caterpilllar Hunt
Eric Eaton

Jul 15, 2015

Female mason wasp, Ancistrocerus campestris, trying to extricate a leaf-tier caterpillar (Psilocorsis sp., Amphisbatidae) from its shelter between two oak leaves. Near Athol, Massachusetts, on June 21, 2015.




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  Maureen Burkle

Location: Rochester, MN

smiling mason wasp  






Created: 8/26/2022

Last Updated:

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