square-headed wasp

(Ectemnius maculosus)

Conservation Status
square-headed wasp (Ectemnius maculosus)
Photo by Alfredo Colon
  IUCN Red List

not listed

 
  NatureServe

not listed

 
  Minnesota

not listed

 
           
           
           
 
Description
 
 

Ectemnius maculosus is a small square-headed wasp. It occurs in the United States east of the Great Plains and across southern Canada.

Adults are (10 mm) in length and black with yellow markings.

The head is large, square, and black. There are two large compound eyes on the sides of the head and three small simple eyes (ocelli) in a triangle on top of the head. The shape of the triangle is low, meaning the sides are shorter than the base. There is a longitudinal ridge in front of the ocelli and a transverse ridge behind the compound eyes. The compound eyes do not have a sharp groove (fovea) on the inner margin. On males, the back of the head is distinctly narrowed behind the compound eyes. The upper part of the forehead (frons) is evenly pitted (punctate). The plate on the face (clypeus) has a large, polished, extension (bevel) on the upper margin. It is entirely black on both sexes. The jaws (mandibles) are mostly yellow above, black just near the tip, and are entirely black below.

The antennae rise low in the face. They consist of a long basal segment (scape), a short connecting segment (pedicel), and a whip-like end section (flagellum) with several segments (flagellomeres). The scape is yellow, the pedicel and flagellum are brown. The first flagellomere is more than twice as long as wide. The second flagellomere is depressed on the underside near the base.

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 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 surface. The band is interrupted in the middle. On the mesothorax, the large front plate (mesoscutum or scutum) is black with no yellow markings. It has transverse microridging in front and longitudinal microridging in the rear. The smaller rear plate (scutellum) has a pair of narrowly separated, yellow spots. The upper surface of the metathorax (metanotum) is entirely black, with no yellow markings. On the lower front of each side of the thorax there is a small yellow spot.

On the rear part of the body the second through fifth segments (tergites) have a pair of narrow, widely separated spots on the front margin. On the fifth tergite the spots are even more widely separated.

The wings are tinted brown. On the forewing there is a single submarginal cell. The recurrent vein ends in the outer third of the submarginal cell.

On all legs the third segment (femur) is black, the fourth segment (tibia) is yellow, and the last part of the leg (tarsus), corresponding to the foot, is yellow. On the front legs the femur has a sharp, rearward-pointing spur near the middle. It does not have a sharp ridge or tooth on the underside near the base.

 
     
 

Size

 
 

(10 mm)

 
     
 

Similar Species

 
     
     
 
Habitat
 
 

 

 
     
 
Biology
 
 

Season

 
 

 

 
     
 

Behavior

 
 

 

 
     
 

Life Cycle

 
 

The nest is usually built in pithy stems. It is provisioned with paralyzed adult flies.

 
     
 

Larva Food

 
 

Flies

 
     
 

Adult Food

 
 

Flower nectar

 
     
 
Distribution
 
 

Distribution Map

 

Sources

29, 30, 82, 83.

 
  5/8/2023      
         
 

Occurrence

 
 

 

 
         
 
Taxonomy
 
 

Order

Hymenoptera (ants, bees, wasps, and sawflies)  
 

Suborder

Apocrita (narrow-waisted wasps, ants, and bees)  
 

Infraorder

Aculeata (ants, bees, and stinging wasps)  
 

Superfamily

Apoidea (bees and apoid wasps)  
 

Family

Crabronidae (square-headed wasps, sand wasps, and allies)  
 

Subfamily

Crabroninae (square-headed wasps)  
 

Tribe

Crabronini  
  Subtribe Crabronina  
 

Genus

Ectemnius  
       
 

Synonyms

 
 

Crabro frigidus

Crabro oblongus

Crabro quadrangularis

Crabro quatuordecimmaculatus

Crabro singularis

Crabro trapezoideus

Ectemnius oblongus

Ectemnius singularis

Ectemnius trapezoideus

Solenius singularis

Solenius trapezoideus

Vespa maculosa

 
       
 

Common Names

 
 

This species has no common name. The name of the subfamily Crabroninae is square-headed wasps, and it is adopted here for convenience.

 

 

 

 

 

 

 

Glossary

Clypeus

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

 

Femur

On insects and arachnids, the third, largest, most robust segment of the leg, coming immediately before the tibia. On humans, the thigh bone.

 

Flagellomere

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

 

Frons

The upper part of an insect’s face, roughly corresponding to the forehead.

 

Ocellus

Simple eye; an eye with a single lens. Plural: ocelli.

 

Pronotum

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

 

Scutum

The forward (anterior) portion of the middle segment of the thorax (mesonotum) in insects and some arachnids.

 

Tarsus

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.

 

Tegula

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.

 

Tergite

The upper (dorsal), hardened plate on a segment of the thorax or abdomen of an arthropod or myriapod.

 

Tibia

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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Alfredo Colon

 
    square-headed wasp (Ectemnius maculosus)      
           
 
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  Alfredo Colon
8/22/2019

Location: Slinger, Wisconsin

square-headed wasp (Ectemnius maculosus)  
           
 
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Created: 5/8/2023

Last Updated:

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