SHARP-EATMAN
NATURE
PHOTOGRAPHY
EPEOLUS AND TRIEPEOLUS CUCKOO BEES
Genus Epeolus
Genus Triepeolus
Brood parasites, sometimes called cuckoo bees or kleptoparasites, enter the nests of host bees to deposit eggs. When a cuckoo's offspring hatch, they eat the host's eggs or slaughter the host's larvae and then feast on the nectar and pollen stores the host carefully gathered for her own offspring.
Brood parasites drink nectar from flowers, and they often appear on the very blossoming plants that their hosts prefer. They do not, however, gather pollen from flowers. As a result, female brood parasites do not have scopae (pollen-collecting hairs) on their legs or abdomens. To the naked eye, they often appear hairless and sleek-bodied like wasps.
Brood parasites sometimes have spade-shaped abdomens or other traits that allow them to dig into other bees' nests, and they generally act differently than their hosts -- many brood parasites spend much of their time skulking around on the ground, looking for their hosts' nests, or lurking outside of nests, waiting for the opportunity to enter them.
WIthin the United States, the tribe Epeolini contains two varieties of brood parasites -- Epeolus and Triepeolus. Bees in these two genera usually have well-defined white or yellow bands on their abdomens and patterns on their thoraxes. These stripes and patterns are made up of short, dense hairs. In the Valley, Epeolus and Triepeolus can be arrestingly beautiful and colorful. Many have red legs and tegulae (the plates where the wing meets the body). Others, like the dwarf Epeolus shown here, have exquisitely-colored eyes.
Epeolus usually parasitize the nests of Colletes (cellophane bees). Cellophane bees protect their nests from moisture by lining their brood-cell walls with a plastic-like substance. The female Epeolus has tooth-like projections on the tip of her abdomen that allow her to saw through the plastic seals of Colletes nests in order to penetrate their egg chambers. The Epeolus then exudes a glue-like substance, which she uses to append her own eggs to chamber walls. When the Epeolus larvae hatch, they feed on the pollen provisions left by the cellophane bee host.
Triepeolus usually target the nests of long-horned bees such as Melissodes and Svastra, and sometimes prey on other ground-nesting bee genera as well (including, among others, Anthophora, Centris, Melitoma, Protaxea and Ptiloglossa).
Triepeolus tend to run larger than Epeolus. In addition, Epeolus and Trepeolus abdomens differ in ways that reflect the characteristics of the nests each cuckoo genus parasitizes. Rather than sport saw-like tools on their abdomens like Epeolus, Triepeolus females have long, narrow, forceps-like projections, which they use to dig into the soil walls of their hosts' underground nests.
Epeolus and Triepeolus cuckoos may be hard to discover, since they have no nests or homes of their own. Thus, they do not form colonies or aggregations. Both males and females sleep outside at night. They sometimes can be found resting in groups in early morning, hanging by their jaws from vegetation frequented by their hosts.
Distinguishing Epeolus from Triepeolus
Triepeolus and Epeolus can be tricky to tell from one another. As noted, Triepeolus are generally larger. The minute differences in the weaponry on the abdomen tips of female Epeolus and Triepeolus bees, detailed above, are not usually visible to the naked eye. Nonetheless, a macro lens can aid in differentiating females of one genus from another. As shown in the accompanying photo strip, the tip of an Epeolus female's abdomen has a characteristic wide patch of silvery hairs.
Identifying Epeolus and Triepeolus species
Epeolus and Triepeolus species within each genus are sometimes difficult to differentiate from one another and may require expert assistance to identify. Helpful information for distinguishing Epeolus species can be found in Thomas Onuferko's “A revision of the cleptoparasitic bee genus Epeolus Latreille for Nearctic species, North of Mexico," noted in this guide's reference page. The best resource for identifying Triepeolus species is Molly Rightmyer's definitive and comprehensive work, “A review of the cleptoparasitic bee genus Triepeolus," also noted in this guide's reference page. Many Triepeolus species in the Lower Rio Grande Valley, however, remain undocumented.
Epeolus species are often differentiated by traits too small to be seen by the naked eye. Nonetheless, some may be distinguished by more obvious traits, such as: (1) the colors of various body parts, particularly the legs, tegulae, face-parts and antennal segments; and (2) the patterns on the bees' thoraxes and abdomens, which are formed by appressed (dense, velvety) pale hairs. (3) In addition, traits of the scutellum (second thorax segment) can be helpful in diagnosing Epeolus species. The hind rim of the Epeolus bee's scutellum bears tooth-like projections called axillae, whose singular shape, color, length or position may be distinctive of a particular species; the shape of the scutellum's hind edge also aids in identification.
Triepeolus species are differentiated by the same traits noted above used to identify Epeolus. The following are also useful for identifying Triepolus species in the Valley: (1) the time of year in which they fly; (2) (in females), the shape of the bee's abdomen tip, as seen from above and in profile; and (3) by characteristics of the clypeus (the face part above the mandibles).
A male Triepeolus
A female dwarf Epeolus cuckoo hanging by its jaws
TRAITS OF EPEOLUS AND TRIEPEOLUS
These pictures show the pseudopygidial areas located at the tips of the abdomens of female Epeolus (left) and Triepeolus (right). To the naked eye, the tip of the female Epeolus abdomen appears covered with a wide band of silvery hairs. On Triepeolus, the pseudopygidial area is narrower and longer, and in most species the bristly hairs covering it have a golden cast.
This is the thorax of a Triepeolus. Patterns on Epeolus and Triepeolus thoraxes are used to differentiate species. Traits of the axillae -- the tooth-like projections on the rear edge of the scutellum (the second thorax segment) are also used to distinguish species.
This is the abdomen of a Triepeolus. The black-and-pale patterns on the abdomens of Triepeolus and Epeolus vary from one species to the next and thus aid in species identification as well.
This is a cellophane bee (genus Colletes). Epeolus cuckoos parasitize the nests of Colletes.
TAXONOMY OF EPEOLUS AND
AND TRIEPEOLUS BEES
Order: Hymenoptera
Family: Apidae
Subfamily: Nomadinae
Tribe: Epeolini
Genus: Epeolus and Triepeolus
Species shown below on this page:
Epeolus pusillus
Triepeolus penicilliferus
Triepeolus rufoclypeus
Triepeolus vernus
Triepeolus zacatecus / kathrynae
Recommended reference on Epeolus:
Onuferko, Thomas M. 2018. A revision of the cleptoparasitic bee genus Epeolus Latreille for Nearctic species, north of Mexico (Hymenoptera, Apidae). ZooKeys 755: 1-185.
Recommended references on Triepeolus:
Rightmyer, Molly .G. 2008. A review of the cleptoparasitic bee genus Triepeolus (Hymenoptera: Apidae). Part I. Zootaxa 1710(1): 1–170. Link.
Onuferko, Thomas M., & Molly G. Rightmyer. 2024. A revision of the simplex species group of the cleptoparasitic bee genus Triepeolus Robertson, 1901 (Hymenoptera: Apidae). European Journal of Taxonomy 950(1): 1–106.
ID GUIDE TO WILD BEES
OF THE NATIONAL BUTTERFLY CENTER
Mission, Texas
CUCKOO BEES
Epeolus & Triepeolus
Epeolus & Triepeolus Species of the National Butterfly Center & Lower Rio Grande Valley
Dwarf Epeolus Cuckoo Bee
Epeolus pusillus
Family: Apidae
Size: 8-9 mm (female)
Food plant at NBC:
Hierba del marrano
(Symphyotrichum sp.)
resinbush
(Viguiera stenoloba)
Plant Family: Asteraceae
When seen at the NBC:
November 2018
April 2019
This is a female dwarf Epeolus. This bee is distinguished in part by its small size: "pusillus" means "small" in Latin.
Epeolus pusillus of the Valley are striking cuckoo bees with red legs and bold black-and-white patterns on the abdomen and thorax. In the Valley, this species tends to have violet eyes.
A female Epeolus pusillus resting while grasping a stem with her jaws
The red legs of a dwarf Epeolus seen from below
A violet-eyed female dwarf Epeolus (Epeolus pusillus)
A female dwarf Epeolus cuckoo bee
At the National Butterfly Center, Epeolus can be found visiting aster-family plants, particularly during the fall. The most common of these is the Epeolus pusillus shown here. This bee is relatively small and easy to miss. ("Pusillus" means "small" ). It preys principally on the correspondingly small compact cellophane bee (Colletes compactus). The two bee species sometimes can be discovered feeding side-by-side on the same plant. Epeolus pusillus also hs been documented parasitizing the nests of Colletes americanus, C. ciliatoides and C. deserticola.
Food plants:
Cowpen daisy
(Verbesina encelioides)
Plant Family: Asteraceae
When and where seen:
Dos Venadas Ranch
Rio Grande City, TX
April 2023
Paintbrush Triepeolus
Triepeolus penicilliferus
Family: Andrenidae
Size: 9-14.5 (males and females)
A male Triepeolus penicilliferus
Male bee
A male Triepeolus penicilliferus measuring 15 mm
Alternate view of bee: the male bee's legs and tegulae are predominantly red.
Dorsal view of thorax
Vertex of male Triepeolus penicilliferus
Triepeolus penicilliferus is a robust and relatively large cuckoo bee whose host species is the large long-horned bee Svastra sabinensis. The male bee shown here measured 15 mm. The bee's legs are predominantly red. It also has red coloration on the tegulae, and on the labrum, clypeus, mandibles and lower antennae.
Spring Triepeolus
Triepeolus vernus
Family: Apidae
Size: 7-10 mm (female)
Associated plants at NBC:
Texas Prickly Pear
Opuntia engelmanii
Twisted rib cactus
Hamatocactus bicolor
Plant family Cactaceae
When seen:
April 2018
A female Triepeolus vernus: this bee has bold black and white patterns on its thorax and abdomen. Its legs are red, as are its tegulae (the plates where the wings join the body).
Dorsal view of bee
Close-up of the bee's thorax (scutum and scutellum)
Pale hairs cover the female bee's mesipisternum (the side of the thorax).
A female spring Triepeolus
A female Triepeolus vernus
Triepeolus vernus appears in April, during the spring cactus bloom in Hidalgo County. It is a small Triepeolus with bright-red markings. Its host species is unknown. In Hidalgo County, however, it frequents areas where Melissodes opuntiellus and Anthophorula compactula are nesting and can be found lurking amid the flowers of twisted-rib cactus, a pollinator plant for both of those species.
Food plants at NBC:
Blanket flower
(Gaillardia pulchella)
Wild sunflower
(Helianthus annuus)
Resinbush
(Viguiera stenoloba)
Seaside goldenrod
Solidago sempervirens
Cowpen daisy
(Verbesina encelioides)
Plant Family: Asteraceae
When and where seen:
NBC & & Rio Grande City, TX
April - October, 2018-2023
Red-faced triepeolus
Triepeolus rufoclypeus
Family: Andrenidae
Size: 8.5-13.5 mm (males & females)
A female Triepeolus rufoclypeus
Female bee
A female Triepeolus rufoclypeus
Dorsal view of a female Triepeolus rufoclypeus
Triepeolus rufoclypeus is the most common Triepeolus of the Valley. It appears in large numbers at the National Butterfly Center in early fall. It is often found on wild sunflowers and other members of the aster family, plants frequented by various long-horned bee species during the same period.
Associated flora
Guajillo
(Senegalia berlandieri)
Plant Family: Fabaceae
When and where seen:
May 16, 2021
La Puerta Tract NWR
(Starr County)
Zacatec or Kathryn's Triepeolus?
Triepeolus zacatecus or
Triepeolus kathrynae?
Family: Apidae
Size: 14-17 mm (female & male)
A male Triepeolus zacatecus / kathrynae: this is a large bee, measuring approximately 16.5 mm. Its head, body and legs are black. Its tegulae are also black and its wings smoky and dark-veined.
Dorsal view of the pattern formed on the bee's thorax by appressed, white hairs: the long axillae are sharply incurved at the tips, and fringed on both the outer and inner margins with white hairs.
Lateral view of head and thorax of male bee
Face of male bee
Recommended References:
Cresson, E.T. 1878. Descriptions of new North American Hymenoptera in the collection of the American Entomological Society". Trans. Amer. Ent. Soc. (Co. Paper 401):61-135. Link.
Onuferko, T.M., & M.G. Rightmyer. 2024. A revision of the simplex species group of the cleptoparasitic bee genus Triepeolus Robertson, 1901 (Hymenoptera: Apidae). European Journal of Taxonomy 950(1): 1–106. Link.
Rightmyer, M.G. 2008. A review of the cleptoparasitic bee genus Triepeolus (Hymenoptera: Apidae). Part I. Zootaxa 1710(1): 1–170. Link.
Rozen J.G. Jr. 1989. Two new species and the redescription of another species of the cleptoparasitic bee genus Triepeolus with notes on their immature stages (Anthophoridae: Nomadinae). American Museum Novitates 2956: 1–18. Link.
See also: Photographs by Dan Jones (Antshrike) of Triepeolus kathrynae. iNaturalist. May 23, 2025. And Comments by Thomas Onuferko and John Ascher dated Dec. 21, 2025. Accessed 12-21-25. Link.
A 16.5 mm male Triepeolus zacatecus / kathrynae
Triepeolus kathrynae or Triepeolus zacatecus?
The male bee specimen featured here, found in Starr County's La Puerta Tract, was first identified in 1991 as Triepeolus zacatecus and appears under this name in Native Bees of the Lower Rio Grande Valley. This species was documented previously in Tamaulipas, the Mexican state that borders Starr County and lies a mere 1-2 miles from La Puerta Tract. E.T. Cresson first described a female of the species in 1878.
Triepeolus zacatecus is a large (15-17 mm), black bee with patterns of short white and pale-yellow hairs on the thorax and abdomen. The bee shown here stood out in the field because of its exceptional size (16.5 mm).
The most comprehensive text on the genus Triepeolus is an impressive 170-page work by Molly Rightmyer published in 2008 and titled ”A review of the cleptoparasitic bee genus Triepeolus (Hymenoptera: Apidae). Part I”. This work covers 103 distinct Triepeolus species. In it, Rightmyer (2008) notes that the black coloration of Triepeolus zacatecus is a key trait that separates it from Triepeolus grandis, a partly-red but otherwise very similar and equally large species, which also occurs in Tamaulipas.
Rightmyer (2008) also notes that Triepeolus zacatecas is "superficially similar to T. kathrynae (in the T. simplex species group), due to the very long axillar spines, the yellow coloration, and the robust body form; however females can easily be separated by the entirely different pseudopygidial areas (apically concave in T. kathrynae)." Differences among males are not discused.
In 2024, the European Journal of Taxonomy published an article coauthored by Epeolini expert Thomas Onuferko and Molly Rightmyer that supplemented the earlier revision. Titled "A revision of the simplex species group of the cleptoparasitic bee genus Triepeolus Robertson, 1901," the new work described eighteen Triepeolus species, among them T. kathrynae. (This article emerged after Native Bees of the Lower Rio Grande Valley entered production.)
Traits of the axillae: Triepeolus kathrynae was first described in 1989 by renowned entomologist Jerome Rozen, Jr., curator of the Apoidea Collection of the American Museum of Natural History. In distinguishing this bee from T. grandis, Rozen noted that T. kathrynae had pale hairs on the sides of the axillae, while T. grandis did not. Axillae, shown in the photographs here, are tooth-shaped features on the rear of the scutellum (the second thorax segment).
Onuferko & Rightmyer (2024) also emphasized traits of the axillae as distinctive features of Triepeolus kathrynae. They noted that on Triepeolus kathrynae, the axillae have pale hairs "all along" their margins; they are large, pointed and hooked; their tips extend well beyond the mid-length of the scutellum; and at least half of the mesal (inner) edges of the axillae are unattached to the scutellum.
T. zacatecus differs in part from this description in having white hairs only along the inner margin of the axillae (RIghtmyer 2008). (Rightmyer 2008 also notes that in the similar T. grandis, both sexes lack hairs all along the margins of the axillae.)
Traits of the sternum: Male Triepeolus kathrynae possess a second distinctive trait highlighted by both Rozen (1989) and Onuferko & Rightmyer (2024): on males, the rear edges of S4–S5 (the fourth and fifth segments of the sternum, or underside of the abdomen) have fringes of dense, long, curved, coppery to silvery hairs. The third sternal segment (S3) lacks such hairs. S3 of Triepeolus zacatecus, by contrast, is fringed with hair. Rightmyer (2008) describes the sternum of the male T. zacatecus as follows: “S3–S5 with apical fringes of setae, white and sometimes reduced on S3, brown to pale golden on S4–S5.”
Conclusions: The sternum of the male bee shown here has dense, curved hairs on S4-S5 but lacks similar hairs on S3. It has conspicuous white hairs all along the outer margins of its axillae as well as shorter hairs along the inner margins. For these reasons, we have concluded that this specimen is a probably a male Triepeolus kathrynae.
Nonetheless, some questions remain about this species diagnosis. The bee shown here is considerably larger (16.5) than the typical length (12-13 mm) of the male Triepeolus kathrynae. Its integument is also entirely black. Both Rozen (1989) and Onuferko & Rightmyer (2024) describe both sexes of Triepeolus kathrynae as being partially red to reddish brown (e.g., on parts of the antennae, most of the legs, parts of the lateral abdomen, the pygidial plate and the tegulae.) All-black variants are found within many Triepeolus species that are typically partially red. Nonetheless, ignoring color differences when identifying T. kathrynae fits uncomfortably with the use of color as a defining trait of T. zacatecas. Finally, since Rightmyer (2008) painstakingly recorded that the fringe of white hairs on S3 is sometimes reduced on T. zacatecus, reliance on traits of S3 could be misleading. Thus the bee's ID hinges primarily on an assessment of traits of the axillae.
In short, the traits distinguishing males of these two species, especially in cases where the bee is all-black, are nuanced and unlikely to be detected by the naked eye or via a field photograph taken from more than a few inches away. When Cresson first described a female Triepeolus zacatecus in 1878, he did not mention the traits of the axillae or sternum now used to separate it from T. kathrynae. It thus seems possible that many early reports of large black Triepeolus resembling T. zacatecus or T. kathrynae could have confused one species with the other.
Additional information on Triepeolus kathrynae
Range: This species ranges through parts of Arizona and New Mexico. There are records of Triepeolus kathrynae from the Mexican states of Baja California, Chihuahua, Durango, Guerrero, Jalisco, Sonora and Morelos. The closest Mexican record is of a male found in 1951 in Vallecillo, Nuevo Leon (approx. 88 miles from La Puerta). There are limited Texas records of Triepeolus kathrynae: it was documented decades ago in Culberson County (1963) and Dimmit County (1943), situated approximately 600 and 120 miles respectively from Starr County.
Records of Triepeolus kathrynae in the Lower Rio Grande Valley are relatively recent. On May 23, 2025, expert nature photographer Dan Jones posted on i-Naturalist photographs of a large, entirely black Triepeolus that he found at La Puerta Tract. This bee was identified as Triepeolus kathrynae by Thomas Onuferko, who accompanied the ID with useful commentary summarizing the distinctive traits of the species.
Host: Triepeolus kathrynae is thought to be a brood parasite of Protoxea. One species of this genus, Protoxea gloriosa, has been documented at La Puerta Tract and elsewhere in the Lower Rio Grande Valley.
[Dec. 23, 2025.]
CITE THIS PAGE: Sharp, Paula and Ross Eatman. "Epeolus and Triepeolus." Wild Bees of the National Butterfly Center of Mission, Texas. 15 Jan. 2019, http://www.wildbeestexas.com. Accessed [day/month/year guide accessed].