Auplopus adjunctus

Small wasp averaging about 10 mm in length. Females possess a distinctive oval pygidial plate on the dorsal surface of the abdomen near the tip, used as a masonry trowel to manipulate mud during nest construction. Males can be distinguished by genitalia differences. Several Auplopus species exhibit bright metallic blue-green coloration; females of these species are externally inseparable, requiring male genitalia examination for definitive identification to species.

Nests are constructed in sheltered microhabitats including pre-existing cavities in wood, spaces under bark on standing trees, rock wall crevices, and abandoned nests of other wasp species such as Sceliphron caementarium, Trypoxylon politum, and Polistes paper wasps. Barrel-shaped mud cells are approximately 15 mm long and 7–10 mm wide, often stacked end-to-end in rows of two to five.

North America; specific range details for A. adjunctus are not well-documented in available sources, though the genus Auplopus occurs across the entire continent.

Adults active from May to October, with peak abundance from July through September.

Adults feed on honeydew from aphid colonies, particularly on honeyvine milkweed (Ampelamus albidus, Cynanchum laeve), sunflower, and other plants. Larvae are provisioned with paralyzed spiders.

• Thomisidae - preycrab spiders
• Salticidae - preyjumping spiders
• Clubionidae - preysac spiders
• Corinnidae - preyground sac spiders (Trachelas sp.)
• Anyphaenidae - preyghost spiders
• Miturgidae - preylonglegged sac spiders (Cheiracanthium sp.)
• Gnaphosidae - preyground spiders
• Pisauridae - preynursery web spiders
• Sceliphron caementarium - nest siteoften builds mud cells inside abandoned nests
• Trypoxylon politum - nest siteoften builds mud cells inside abandoned nests
• Polistes - nest siteoften builds mud cells inside abandoned paper wasp nests

Female constructs mud cell, provisions it with one or more paralyzed spiders (often with legs amputated to facilitate transport), lays a single egg on the final spider victim, and seals the cell. Larva hatches and consumes the paralyzed prey, then pupates within the cell. In at least one congeneric species, the emerging adult regurgitates liquid to soften the mud cap before chewing an exit hole. Some individuals may overwinter as pupae.

Females are solitary nest builders. They amputate several or all legs of spider prey, which facilitates ground transport and allows the wasp to feed on spider blood. Adults are not aggressive and rarely sting unless handled. Seldom visit flowers.

Predator of spiders, contributing to arthropod population regulation. As a solitary wasp, provides limited pollination services through incidental contact. Serves as host for various parasitoid species, though specific parasite relationships remain poorly documented.

Not medically significant; stings are possible but uncommon and not considered dangerous. Mud nests may be encountered on structures and sometimes mistaken for signs of more aggressive social wasps. Nests can be reared by citizen scientists to document host-parasite relationships.

• EumenesPotter wasps construct urn-shaped mud nests with fluted necks, provisioned with caterpillars rather than spiders; nests are typically more exposed and vase-like rather than barrel-shaped.
• Trypoxylon politumPipe organ mud dauber constructs linear mud tubes with internal partitions, often with male-female cooperative nest defense; nests are tubular rather than barrel-shaped.
• Sceliphron caementariumBlack and yellow mud dauber builds larger, clod-like multi-cell nests covered with additional mud layers; much larger wasp with different coloration.
• OsmiaSome mason bees construct similar mud nests; bees are vegetarians provisioning nests with pollen/nectar rather than spiders, and have different adult morphology.

• 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