Symmorphus projectus

Distinguished from other North American Symmorphus species primarily by geographic distribution: strictly western from Pacific Northwest to Montana, Wyoming, and southward, whereas S. albomarginatus, S. canadensis, and S. cristatus are more widespread or eastern. From S. canadensis (smallest species) by larger size. From S. cristatus and S. albomarginatus by range. Generic characters include horizontal carina and vertical groove on first abdominal tergite, and simple last antennal segment in males. Specific diagnostic features for S. projectus within the genus are not detailed in available sources.

Found in association with dead, standing or fallen trees with beetle borings, particularly those made by deathwatch beetles (family Ptinidae, formerly Anobiidae). Uses pre-existing wood cavities including beetle exit holes in dead cottonwoods and other trees, hollow twigs, or stems. Nests in shaded locations or on the shady side of trees. Readily uses artificial nest blocks with holes 3-4 mm in diameter placed in sheltered situations such as under eaves or in firewood stacks.

Strictly western North America: Pacific Northwest (Washington, Oregon, British Columbia) eastward to Montana and Wyoming, and southward (California, Nevada, Utah, Colorado, Arizona, New Mexico). Not found in eastern North America where congeners S. albomarginatus, S. canadensis, and S. cristatus occur.

Adults feed on honeydew (sweet liquid waste secreted by aphids). Females provision nests with paralyzed larvae of leaf beetles (Chrysomelidae), weevils (Curculionidae), or leaf-mining moth caterpillars as food for offspring.

• leaf beetles - preylarvae paralyzed and stored as food for wasp offspring
• weevils - preylarvae paralyzed and stored as food for wasp offspring
• leaf-mining moths - preycaterpillars occasionally taken; primarily leaf-mining species
• aphids - food source for adultsadults consume honeydew secreted by aphids
• deathwatch beetles - nest site provideruses exit holes made by emerging beetles in family Ptinidae (formerly Anobiidae)

Females use pre-existing cavities in wood, hollow twigs, or stems. They partition tunnels into multiple cells using mud curtains, working from back to front. Each cell receives one egg, then is provisioned with paralyzed prey larvae. Number of prey per cell depends on prey size and offspring sex (female larvae require more food). Completed nests typically contain multiple cells; often includes an empty 'vestibular' cell at entrance and sometimes 'intercalary' vacant cells between provisioned cells, possibly as defense against parasites. One 7-cell nest of congeneric S. canadensis was completed in about three days. Developmental timing not specified for S. projectus specifically.

Solitary nesting behavior. Females hunt prey, paralyze it with sting, and transport to nest. They modify pre-existing cavities by chewing wood fibers to expand entrances or plastering with mud/resin to shrink them, though prefer holes that fit without modification. Females can control offspring sex through egg fertilization. Males harass females for mating opportunities; multiple males may compete, causing females to tumble from nest entrances. Adults frequently visit aphid colonies to feed on honeydew.

Predator of leaf beetle larvae, weevil larvae, and leaf-mining moth caterpillars, helping to control populations of these herbivores that can defoliate trees and shrubs. Prey specialization makes it a targeted biological control agent in its habitat. Serves as host for parasitic cuckoo wasps (Chrysididae), eulophid wasps (Melittobia), torymid wasps (Monodontomerus), and satellite flies (Amobia), contributing to food web complexity. Nest cavities used after abandonment may provide habitat for other organisms.

Beneficial insect that helps control leaf beetle and weevil populations in gardens, orchards, and forests. Readily accepts artificial nest blocks ('bee condos'), making it accessible for citizen science observation and backyard conservation. Does not sting humans unless handled. Not a structural pest—does not create its own holes in wood, only uses pre-existing cavities. Can be encouraged by preserving dead standing trees or installing wooden blocks with 3-4 mm holes in sheltered locations.

• Symmorphus cristatusOverlaps in western range; distinguished by broader transcontinental distribution extending eastward, and subtle morphological differences not detailed in sources.
• Symmorphus canadensisOverlaps in western range; distinguished by smaller size (smallest North American Symmorphus) and broader transcontinental distribution except Florida, Texas, New Mexico, and Arizona.
• Symmorphus albomarginatusDistinguished by range—found from Alaska to California, New Mexico, Quebec, and eastern U.S., not strictly western.
• Trypoxylon spp.Co-occurs in beetle borings; distinguished by extremely slender 'thread-waisted' body form, different prey (spiders rather than beetle larvae), and different nest closure (typically plugs with mud rather than partitioning cells).
• Passaloecus spp.Co-occurs in beetle borings; smaller aphid wasps with different prey (aphids rather than beetle larvae) and different body proportions.

• mason wasp
• potter wasp
• solitary wasp
• leaf beetle predator
• cavity nester
• western North America

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• Catalogue of Life
• Bug Eric: Wasp Wednesday: Symmorphus
• Bug Eric: Wasp vs. Wasp
• Bug Eric: A "Boring" Place to Nest