Cavity-nester
Guides
Isodontia elegans
Elegant Grass-carrying Wasp
Isodontia elegans is a solitary, nest-provisioning thread-waisted wasp in the family Sphecidae. Commonly known as the elegant grass-carrying wasp, it hunts orthopteran prey including tree crickets and katydids, which it paralyzes and stores in nest cells for its developing larvae. The species is notable for using pre-existing cavities—particularly window tracks and wind chime tubes in suburban settings—lining them with finely chewed grass fibers that serve as both partitions between cells and defensive barriers against parasites.
Isodontia exornata
grass-carrier wasp
Isodontia exornata is a solitary thread-waisted wasp in the family Sphecidae, commonly known as a grass-carrier wasp. Females construct nests using dry grass in pre-existing cavities such as window tracks, hollow stems, or abandoned insect tunnels. They provision each nest cell with paralyzed tree crickets or katydids as food for their larvae. The species is part of the genus Isodontia, which includes several North American species that have adapted to suburban environments by utilizing human-made structures for nesting.
Isodontia mexicana
Mexican Grass-carrying Wasp, Grass-carrying Wasp
Isodontia mexicana is a solitary sphecid wasp native to North America that has become a successful invasive species in Europe since the 1960s. Females construct nests in pre-existing cavities such as hollow stems, abandoned beetle tunnels, or even window tracks, lining them with grass fragments. They provision nests with paralyzed orthopteran prey—primarily small katydids (Tettigoniidae) and tree crickets (Gryllidae, particularly Oecanthinae)—to feed their larvae. The species is notable for its splayed wing posture at rest and has been observed visiting diverse flowering plants for nectar.
Isodontia philadelphica
Grass-carrying Wasp
Isodontia philadelphica is a solitary wasp in the family Sphecidae, commonly known as a grass-carrying wasp. Females construct nests in pre-existing cavities such as hollow stems, abandoned insect burrows, or window tracks, using dry grass to partition cells and plug entrances. They provision nests with paralyzed tree crickets and katydids as food for their larvae. The species occurs in North America and is not aggressive toward humans.
Leucospis affinis affinis
Leucospis affinis affinis is a chalcidoid wasp in the family Leucospidae, notable for being among the largest members of its superfamily. Females are distinguished by an ovipositor that curves over the dorsal abdomen, used to drill into wood and parasitize solitary bees nesting in pre-existing cavities. The subspecies is primarily a parasite of megachilid bees including leafcutter bees (Megachile), mason bees (Osmia), and resin bees (Dianthidium). Larvae develop as external parasites attached to host bee larvae, completing development in approximately 7–12 days before pupating within the host's cocoon.
Megachile
Leafcutter bees, Leafcutting bees, Resin bees, Mortar bees
Megachile is a large, cosmopolitan genus of solitary bees in the family Megachilidae, comprising over 1,500 described species across more than 50 subgenera. The genus includes the commercially important alfalfa leafcutter bee (M. rotundata), managed globally for crop pollination. Species exhibit diverse nesting strategies: many cut circular leaf or petal pieces to line nest cells, while others use plant resin or mortar-like materials. The genus contains the world's largest bee, M. pluto (Wallace's Giant Bee), with a wingspan exceeding 6 cm.
Megachile gentilis
Megachile gentilis is a solitary leafcutter bee in the family Megachilidae, described by Cresson in 1872. It is a non-metallic, robust black bee that constructs nests using leaf pieces or plant resin. Females carry pollen on the underside of the abdomen and create "bee loaves" of pollen, nectar, and saliva to provision brood cells. The species has been recorded in North America, Middle America, and Oceania.
Megachile odontostoma
Megachile odontostoma is a species of leafcutter bee in the family Megachilidae, described by Cockerell in 1924. The species belongs to a large genus of solitary bees characterized by females that cut leaves or petals to line their nest chambers. As with other Megachile species, females carry pollen on specialized hairs (scopa) on the underside of the abdomen rather than on the hind legs. The specific epithet "odontostoma" refers to toothed mouthparts, though detailed morphological studies of this particular species remain limited.
Megachile policaris
Texas leafcutter bee, policaris leafcutter bee
Megachile policaris is a large, solitary leafcutter bee native to North America that has established invasive populations in Hawaiʻi. First detected on Oʻahu in 2017, it is now present on multiple Hawaiian islands including Maui, Kauaʻi, and Hawaiʻi Island. It is among the largest Megachile species in North America, with females reaching 18–22 mm. The species constructs nests in pre-existing cavities and uses cut leaf pieces to line brood cells.
Megachile pugnata
Pugnacious Leafcutter Bee, Sunflower Leafcutting Bee
Megachile pugnata is a solitary, cavity-nesting leafcutter bee native to North America. Females construct nests in preexisting hollow cavities using cut leaves to line brood cells, which are partitioned by plugs of mud, sand, or vegetation. Adults feed exclusively on flowers in the Asteraceae family, making them particularly effective pollinators of sunflowers. The species exhibits strong instinctive aggregation behavior, with females preferentially nesting near conspecifics even when cavities are abundant. Males emerge before females in spring, mate quickly, and die, while females live approximately two months and produce 35-40 eggs across multiple nests.
Megachile pugnata pugnata
sunflower leafcutting bee
Megachile pugnata pugnata is a solitary leafcutting bee native to North America, notable for its specialized association with sunflowers (Helianthus). Females construct nests in pre-existing cavities using circular leaf pieces cut from host plants to form thimble-shaped brood cells. The subspecies exhibits strong instinctive aggregation behavior, preferentially clustering nests even when suitable cavities are abundant. It develops through complete metamorphosis with overwintering as a prepupa, and has been managed commercially for sunflower pollination.
Megachile relativa
Golden-tailed Leafcutter Bee
Megachile relativa is a solitary leafcutter bee in the family Megachilidae, described by Ezra Townsend Cresson in 1878. The species nests in pre-existing cavities such as trap-nests and has been documented in Wisconsin and Vermont. Like other members of the genus Megachile, females carry pollen on scopal hairs beneath the abdomen rather than on the hind legs.
Megachile rotundata
Alfalfa Leafcutter Bee, Alfalfa Leaf-Cutter Bee, Leafcutter Bee
Megachile rotundata is a solitary leafcutting bee native to Europe and the Mediterranean region, now widely established as a managed pollinator across North America and other continents. It is the second most important commercial pollinator globally after the honey bee, specifically renowned for its efficiency in alfalfa pollination. Females construct individual nests in pre-existing cavities, lining cells with precisely cut circular leaf pieces. The species is non-aggressive, does not produce honey, and has been introduced deliberately and accidentally to multiple regions for agricultural pollination services.
Megachile sculpturalis
giant resin bee, sculptured resin bee
Megachile sculpturalis is a large solitary leafcutting bee native to Japan, China, and South Korea. First detected in North Carolina in 1994, it has become established across much of eastern North America and has spread rapidly through Europe since its first detection near Marseille, France in 2008. Females are notably larger than males and use their powerful mandibles to collect plant resin for sealing brood cells. Unlike carpenter bees, M. sculpturalis cannot excavate wood and relies entirely on pre-existing cavities, particularly abandoned galleries of carpenter bees (Xylocopa spp.) in wooden structures.
Megachile zaptlana
Megachile zaptlana is a solitary leafcutter bee in the family Megachilidae, first described by Cresson in 1878. The species belongs to the subgenus Sayapis and has been documented across the Americas from the southern United States through Central America to South America. As a member of the genus Megachile, it exhibits the characteristic trait of cutting leaves or other plant materials to line its nest cavities. Research indicates it utilizes pre-existing cavities for nesting and shows specific floral associations, though detailed natural history remains incompletely documented.
Mischocyttarus flavitarsis
Western Paper Wasp, Yellow-legged Paper Wasp
Mischocyttarus flavitarsis is a social paper wasp native to western North America, distinguished by its relatively docile defensive behavior compared to other vespids. Colonies are initiated in spring by foundress queens and persist until autumn, with nests typically containing fewer than 300 cells. The species exhibits flexible nesting habits, utilizing both natural cavities in riparian forests and anthropogenic structures such as building eaves. Unlike many social wasps, M. flavitarsis rarely stings, instead employing ramming behavior against perceived threats. Males engage in elaborate lekking and territorial scent-marking behaviors near female hibernation sites in autumn.
Monobia
Four-toothed Mason Wasp (for M. quadridens), Carpenter Wasp, Mason Wasp
Monobia is a genus of medium-sized to large potter wasps in the subfamily Eumeninae, distributed primarily across the Neotropical region from the United States to Argentina. The genus is closely related to Montezumia. The most well-documented species, Monobia quadridens (Four-toothed Mason Wasp), is a solitary wasp that provisions nests with paralyzed caterpillars and constructs mud partitions between brood cells.
Monobia arizonensis
Monobia arizonensis is a species of mason wasp in the subfamily Eumeninae. Like other members of the genus Monobia, it is presumed to be a solitary wasp that utilizes pre-existing cavities for nesting. The species is native to the southwestern United States, specifically Arizona. Very little specific information has been published about its biology compared to the better-known congener Monobia quadridens.
Monobia quadridens
Four-toothed Mason Wasp, Carpenter Wasp
Monobia quadridens is a solitary potter wasp in the subfamily Eumeninae, native to eastern North America. Adults are striking black-and-white insects with a distinctive broad ivory band across the first abdominal tergite. The species is bivoltine, producing two generations annually, with one generation overwintering as pupae. Females construct multi-celled nests in pre-existing cavities, provisioning each cell with paralyzed caterpillars for their larvae.
Osmia aglaia
Oregon berry bee
Osmia aglaia is a solitary mason bee native to the western United States. It is commonly known as the Oregon berry bee due to its specialized role as a pollinator of brambles, particularly raspberries and blackberries. The species exhibits metallic coloration and nests in pre-existing wood tunnels. Adults are active in late spring, coinciding with Rubus bloom periods.
Osmia bucephala
bufflehead mason bee
Osmia bucephala, commonly known as the bufflehead mason bee, is a solitary bee species in the family Megachilidae native to North America. As a mason bee, it nests in pre-existing tubular cavities and uses mud to construct and seal brood cells. The species is part of the diverse Osmia genus, which includes many ecologically important pollinators. Limited specific ecological data is available for this species compared to better-studied congeners such as O. lignaria.
Osmia coloradensis
Colorado Mason, Colorado osmia
Osmia coloradensis is a solitary mason bee in the family Megachilidae, native to western North America. Like other Osmia species, it nests in pre-existing cavities such as hollow plant stems or holes in wood, sealing nest chambers with mud. The species is recognized as a native pollinator with documented observations across multiple western U.S. states and parts of Central America. It belongs to a genus of bees increasingly valued for orchard pollination services, though specific management practices for this species are less developed than for commercially used relatives.
Osmia glauca
Osmia glauca is a species of mason bee in the family Megachilidae, originally described as Heriades glaucum by Fowler in 1899. It is native to North America and belongs to a genus of solitary bees known for nesting in pre-existing cavities and sealing brood cells with mud. Like other Osmia species, it is likely a pollinator of flowering plants, though specific ecological details remain poorly documented.
Osmia lignaria
blue orchard bee, orchard mason bee, BOB
A solitary megachilid bee native to North America, widely managed for pollination of early spring fruit crops including almonds, apples, and cherries. Distinguished by metallic blue coloration, smaller size than honey bees, and unique mud-nesting behavior. Divided into two subspecies by the Rocky Mountains: O. l. propinqua (west) and O. l. lignaria (east).
Osmia lignaria propinqua
Western Blue Orchard Bee, Blue Orchard Bee, BOB
Osmia lignaria propinqua is a solitary, cavity-nesting mason bee native to western North America, commonly known as the Western Blue Orchard Bee or BOB. It is a subspecies of the blue orchard bee and is valued as a highly efficient pollinator of early-blooming fruit trees including almonds, cherries, apples, and plums. Females carry dry pollen on the scopa (hairs) beneath the abdomen rather than on leg baskets, and they forage at lower temperatures and for more hours than honey bees. The species is managed commercially in orchards, where it is often deployed alongside honey bees to improve cross-pollination through its tendency to move between trees rather than forage systematically on single plants.
Osmia pumila
Osmia pumila is a solitary mason bee native to eastern North America. It is strongly associated with forest habitats, where it performs spring pollination of wildflowers and possibly some timber trees. The species nests in pre-existing cavities such as hollow stems or holes in wood, sealing brood chambers with mud. Research indicates it is one of the most common forest-associated bee species in the eastern United States, with populations increasing as forest cover has regrown since the early 1900s.
Osmia simillima
Osmia simillima is a solitary mason bee in the family Megachilidae, native to North America. It nests in twigs, buried wood, and has been observed using oak apple galls as nesting sites. As a member of the genus Osmia, it belongs to a group of ecologically important pollinators that use mud to construct and seal nest chambers.
Pachodynerus erynnis
Red-marked Pachodynerus Wasp, Red and Black Mason Wasp
Pachodynerus erynnis is a solitary mason wasp that specializes in hunting caterpillars to provision its nests. Unlike social wasps, it does not form colonies but constructs individual nests in pre-existing cavities. The species is valued as a biological control agent, targeting economically significant caterpillar pests including armyworms, cutworms, and loopers. Its frequent visits to flowers for nectar make it a minor pollinator as well.
Pachodynerus guadulpensis
Pachodynerus guadulpensis is a solitary mason wasp native to the Americas, ranging from Mexico through Central America into the southern United States (Arizona, California, Texas). This species belongs to the potter and mason wasp subfamily Eumeninae. Females construct linear nests of cylindrical mud cells in pre-existing cavities, primarily provisioning them with paralyzed caterpillars as food for their larvae. The species exhibits distinctive abdominal coloration with an extra yellow stripe across the front of the abdomen that separates it from its congener P. nasidens.
Pachodynerus nasidens
Keyhole Wasp
Pachodynerus nasidens, commonly known as the keyhole wasp, is a solitary mason wasp in the family Vespidae, subfamily Eumeninae. Native to the Neotropics, it has been introduced to Hawaii, Micronesia, Australia, and the northern United States. The species exhibits remarkable nesting plasticity, utilizing abandoned insect galleries, human-made cavities, and even aircraft pitot tubes. Females provision nests with paralyzed caterpillars as food for their larvae. The species has gained notoriety for causing aviation safety incidents by blocking pitot probes with mud nests, leading to unreliable airspeed readings.
Pachodynerus pulverulentus
Keyhole wasp
Pachodynerus pulverulentus is a solitary mason wasp in the subfamily Eumeninae, commonly known as a keyhole wasp. It belongs to a genus of wasps that utilize pre-existing cavities in wood—such as abandoned beetle galleries, old nail holes, or hollow twigs—as nesting sites. Like other Pachodynerus species, females provision these cavities with paralyzed caterpillars as food for their developing larvae. The species was described by Viereck in 1908 and is part of a group of wasps known for their opportunistic nesting behavior and importance as biological control agents of caterpillar pests.
Parancistrocerus
potter wasps, mason wasps
Parancistrocerus is a large genus of solitary potter wasps in the subfamily Eumeninae, distributed across the Nearctic, eastern Palearctic, Oriental, and Neotropical regions. The genus is distinguished by a unique morphological feature: a smooth depression at the base of the second metasomal tergum that functions as an acarinarium, providing shelter for symbiotic deutonymphs of mites in the family Winterschmidtiidae. Species are often difficult to distinguish from the related genus Stenodynerus, sharing medial pits on the anterior pronotum and expanded tegulae. Most species possess a transverse carina on the first metasomal tergum, and many Neotropical species exhibit a faint submetallic body luster.
Parancistrocerus bicornis
Parancistrocerus bicornis is a small mason wasp in the subfamily Eumeninae, described by Roberts in 1901. Like other members of the genus, it is a solitary, cavity-nesting wasp that provisions its nests with paralyzed caterpillars as food for its larvae. The species is part of a taxonomically challenging group where live specimens and even microscope examination often cannot reliably distinguish between closely related species such as Parancistrocerus and Stenodynerus.
Parancistrocerus bicornis ceanothi
Parancistrocerus bicornis ceanothi is a subspecies of mason wasp in the subfamily Eumeninae. It belongs to a genus of small, solitary cavity-nesting wasps that provision their nests with paralyzed caterpillars. The subspecies name "ceanothi" suggests a potential association with Ceanothus host plants, though this relationship requires verification. Like other Parancistrocerus species, it likely nests in pre-existing cavities such as hollow twigs or beetle borings.
Parancistrocerus fulvipes
potter wasp
Parancistrocerus fulvipes is a solitary mason wasp in the family Vespidae, commonly known as the potter wasp. The species is recognized for its flexible nesting behavior, utilizing pre-existing cavities rather than constructing free-standing mud pots. It provisions nests with paralyzed caterpillars as food for its larvae. Two subspecies are recognized: P. f. fulvipes and P. f. rufovestis.
Parancistrocerus pedestris
Parancistrocerus pedestris is a small solitary mason wasp in the family Vespidae, subfamily Eumeninae. The species was first described by de Saussure in 1856. Like other members of its genus, it is a cavity-nesting wasp that provisions its nests with paralyzed caterpillars as food for its larval offspring. The species is part of a taxonomically challenging group where live specimens are often difficult to distinguish from related species without microscopic examination.
Parancistrocerus pensylvanicus
Pennsylvania mason wasp
Parancistrocerus pensylvanicus is a solitary mason wasp in the subfamily Eumeninae. It is a cavity-nesting species that provisions nests with paralyzed caterpillars as food for its larvae. The species has been documented in the northeastern United States, including Vermont. Like other members of its genus, it is difficult to distinguish from closely related species such as Stenodynerus without microscopic examination.
Parancistrocerus perennis
two-banded mason wasp, perennial mason wasp
Parancistrocerus perennis, commonly known as the two-banded mason wasp or perennial mason wasp, is a small solitary wasp in the subfamily Eumeninae. It is native to eastern North America, ranging from southern Ontario to Florida and west to the Mississippi River. The species is a cavity-nesting predator that hunts specific caterpillar families to provision its nests. Two subspecies are recognized: P. p. perennis and P. p. anacardivora, the latter occurring in southern populations and distinguished by reddish markings.
Parancistrocerus perennis anacardivora
Parancistrocerus perennis anacardivora is a southern subspecies of the mason wasp Parancistrocerus perennis, distinguished by reddish markings along the side of the first abdominal segment. It is a small solitary wasp with a wing length of 6-8 millimeters. Females hunt caterpillars to provision nest cells in hollow twigs or pre-existing cavities, paralyzing prey with their sting. The subspecies ranges from southern Ontario to Florida and west to the Mississippi River, with anacardivora occurring in the southern portion of this range.
Parancistrocerus perennis perennis
mason wasp
Parancistrocerus perennis perennis is a small solitary mason wasp in the subfamily Eumeninae. Females hunt caterpillars of leafroller moths (Tortricidae) and casebearer moths (Coleophoridae), paralyzing them with their sting to provision nest cells in hollow twigs. The subspecies is distinguished from the southern P. p. anacardivora by lacking reddish markings on the first abdominal segment. It ranges from southern Ontario to Florida and west to the Mississippi River.
Parancistrocerus texensis
Parancistrocerus texensis is a species of solitary mason wasp in the subfamily Eumeninae. It is one of numerous small, cavity-nesting wasps in the genus Parancistrocerus that provision their larvae with paralyzed caterpillars. The species was described by Henri de Saussure in 1871, with the epithet suggesting a Texas origin. Like other members of its genus, it is difficult to distinguish from congeners without microscopic examination, and is frequently confused with similar genera such as Stenodynerus.
Parancistrocerus vagus
Parancistrocerus vagus is a small solitary mason wasp in the subfamily Eumeninae. It belongs to a genus of cavity-nesting wasps that provision their young with paralyzed caterpillars. The species was described by de Saussure in 1857. Limited specific information is available for this species, though genus-level traits suggest typical mason wasp biology including use of pre-existing cavities and caterpillar prey.
Passaloecus
Picket-boring Aphid Wasps
Passaloecus is a genus of small solitary wasps in the family Crabronidae, commonly known as picket-boring aphid wasps. The genus comprises approximately 40-48 species worldwide, with strong representation in both the Nearctic and Palearctic regions. These diminutive wasps, typically 6-8 mm in body length, are specialized predators of aphids and serve as important biological control agents. Females construct nests in pre-existing cavities such as beetle borings in dead wood, hollow stems, and artificial trap nests, provisioning cells with paralyzed or dead aphids for their larval offspring.
Passaloecus annulatus
Passaloecus annulatus is a small solitary wasp in the family Crabronidae, subfamily Pemphredoninae. Females hunt aphids as food for their larval offspring and also feed on aphid honeydew. The species nests in pre-existing cavities such as beetle borings in dead wood, hollow stems, or vacant galls, partitioning these into linear series of cells. It occurs across North America.
Passaloecus cuspidatus
aphid wasp
Passaloecus cuspidatus is a small solitary wasp in the family Crabronidae, subfamily Pemphredoninae. It is an aphid predator that provisions its nests with paralyzed or dead aphids as food for its larvae. The species is found in North America, including Canada and the United States. Like other members of its genus, it nests in pre-existing cavities such as beetle borings in dead wood, hollow stems, and vacant galls.
Pemphredonini
Pemphredonini is a tribe of small, solitary wasps within the subfamily Pemphredoninae (family Crabronidae). These apoid wasps are commonly known as aphid wasps due to their specialized predation on aphids and other small Hemiptera. The tribe contains multiple genera, including the widespread Pemphredon. Adults are often observed visiting flowers for nectar.
Poemenia
Poemenia is a genus of ichneumonid wasps in the subfamily Poemeniinae. The genus comprises ectoparasitoids that attack small xylophilous bees (Apoidea) nesting in tunnels or cavities. Larval morphology indicates an ectoparasitoid lifestyle, with the mature larva of Poemenia albipes being the first described for the genus.
Pseudodynerus
mason wasps, potter wasps
Pseudodynerus is a small Neotropical genus of potter wasps (Eumeninae) currently containing 16 recognized species. These solitary mason wasps are characterized by their striking black and white coloration and their habit of nesting in pre-existing cavities in wood. Females provision their nests with paralyzed caterpillars as food for their developing larvae. The genus extends northward into the eastern United States, where at least one species, P. quadrisectus, is well-documented.
Pseudodynerus quadrisectus
Pseudodynerus quadrisectus is a solitary mason wasp native to eastern North America. First described by Thomas Say in 1837, this species is frequently mistaken for the similar Four-toothed Mason Wasp (Monobia quadridens). Females construct multi-celled nests in pre-existing wood cavities, provisioning each cell with paralyzed caterpillars as food for their larvae. The species is considered beneficial in gardens due to its pollination activity and caterpillar predation.
Stenodynerus
Stenodynerus is a large genus of potter wasps (subfamily Eumeninae) distributed across the Nearctic, Palearctic, Oriental, and Neotropical regions. Females are known to provision nests with paralyzed caterpillars as food for their larvae. The genus is morphologically close to Parancistrocerus, Hypancistrocerus, and Eustenancistrocerus, with which it shares diagnostic features including medial pits on the anterior pronotum and expanded tegulae. Most species lack a transverse carina on the first metasomal tergum.