Auplopus architectus metallicus

Distinguished from other spider wasp genera by the construction of free-standing mud cells rather than burrows or use of pre-existing cavities. Separated from other mud-nesting wasps (Eumenes, Sceliphron, Trypoxylon) by the small size of the mud cells (roughly 15 mm long by 7-10 mm wide), barrel shape, and tendency to stack cells end-to-end in rows of 2-5. Differs from mason bees (Osmia) and mason wasps (Eumeninae) by cell arrangement and wasp body form. As a subspecies, distinguished from the nominate A. architectus architectus by subtle morphological differences, though specific diagnostic characters require taxonomic revision.

Small wasp, approximately 10 mm in length. Females possess an oval pygidial plate on the dorsal surface of the abdomen near the tip, used as a masonry trowel for manipulating mud pellets during nest construction. Several Auplopus species are bright metallic blue-green; females of different species are often externally indistinguishable, while males can be separated by genitalia differences.

Nests are constructed in sheltered microhabitats: pre-existing cavities in wood, under bark on standing trees, rock wall crevices, or inside abandoned nests of other wasp species (Sceliphron caementarium, Trypoxylon politum, Polistes spp.). Adults are found around aphid colonies on plants such as honeyvine milkweed (Ampelamus albidus, Cynanchum laeve) and sunflower, where they feed on honeydew.

North America. The genus Auplopus occurs across the entire continent; specific distribution of A. architectus metallicus requires further documentation, though the species A. architectus is known from western North America.

Active from May through October, with peak abundance July through September.

Adults feed on honeydew from aphid colonies. Larvae are provisioned with paralyzed spiders; documented prey includes spiders from at least thirteen families: Thomisidae (crab spiders), Salticidae (jumping spiders), Clubionidae (sac spiders), Corinnidae (ground sac spiders), Anyphaenidae (ghost spiders), Miturgidae (longlegged sac spiders), Gnaphosidae (ground spiders), and Pisauridae (nursery web spiders). Prey legs are often amputated to facilitate transport and to allow the wasp to feed on spider blood.

Female constructs mud cell, provisions it with one or more paralyzed spiders, lays a single egg on the last victim, and seals the cell. Larva hatches, consumes the fresh prey (paralyzed spiders do not spoil), pupates within a cocoon inside the cell. In at least some species, the emerging adult regurgitates liquid to soften the mud cap before chewing through to exit. Development time varies; some individuals may overwinter as pupae.

Females are solitary nest builders. They hunt spiders opportunistically, amputating legs to facilitate transport back to the nest. Multiple cells are often constructed in a series, stacked end-to-end. Adults are seldom seen at flowers but regularly visit aphid colonies for honeydew. Solitary wasps are non-aggressive and do not defend nests actively.

Predator of spiders, potentially influencing spider population dynamics. As a solitary wasp, contributes to nutrient cycling through prey capture and larval development. Mud nest construction may provide secondary habitat for nest parasites and commensals.

Non-aggressive; does not sting unless handled. Nests are sometimes considered unsightly when attached to human structures, but destruction is unnecessary as females abandon nests after sealing them. Nests can be collected for rearing to study host-parasite relationships, as many parasite species may emerge.

• Eumenes (potter wasps)Also construct mud nests, but build urn-shaped pots with fluted necks, not barrel-shaped cells. Stock nests with caterpillars rather than spiders.
• Sceliphron caementarium (black and yellow mud dauber)Builds larger, clod-like mud nests with multiple cells covered in additional mud layers. Nests are heavier and usually placed under rock overhangs or man-made structures.
• Trypoxylon politum (pipe organ mud dauber)Constructs adjacent mud tubes (resembling pipe organs) with internal cell partitions, often built in pairs with male guarding behavior. Linear cell arrangement differs from Auplopus barrel stacks.
• Phanagenia bombycinaLarger Auplopini wasp found east of the Rocky Mountains; also builds mud barrels but often inside abandoned Trypoxylon nests.
• Osmia (mason bees)Some species construct similar mud cells, but are bees (Hymenoptera: Megachilidae) with different body form and pollen-collecting behavior rather than spider hunting.

• spider wasp
• mud nest
• solitary wasp
• Pompilidae
• Auplopini
• predator
• spider hunter
• metallic wasp

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• Catalogue of Life
• Bug Eric: Masters of Mud: Auplopus Spider Wasps
• Bug Eric: Mud Masterpieces
• Bug Eric: January 2010
• Oecanthidae | Beetles In The Bush