SHARP-EATMAN
NATURE
PHOTOGRAPHY
EPEOLUS AND TRIEPEOLUS CUCKOO BEES
Genus Epeolus
Genus Triepeolus
Cuckoo bees break into nests of other bees. Sometimes, the cuckoos devour the eggs of the host bees that built the nests. More commonly, the cuckoos simply deposit their own eggs in the host bees' nests and depart. 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. In the world of entomology, cuckoo bees are known as cleptoparasites or brood parasites.
Cuckoo bees do not gather pollen from flowers, because they obtain it instead by plundering other bees' nests. As a result, female cuckoo bees do not have scopae (pollen-collecting hairs) on their legs or abdomens. To the naked eye, cuckoo bees often appear hairless and sleek-bodied like wasps.
Cuckoos sometimes have spade-shaped abdomens or other traits that allow them to dig into other bees' nests, and cuckoos generally act differently than their hosts -- many cuckoos spend much of their time skulking around on the ground, looking for their hosts' nests, rather than visiting flowers. Cuckoo bees do, however, drink nectar from flowers, and they often appear on the very blossoming plants that their hosts prefer.
The bee tribe Epeolini contains two varieties of cuckoo bee found within the United States -- Epeolus and Triepeolus. Bees in these two genera are often mistaken for wasps. They have well-defined black-and-white bands striping their abdomens and often sport bold black-and white patterns on their thoraxes as well. These bees 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 cellophane bees of the genus Colletes. 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 ends 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 mother cellophane bee.
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 and Melitoma).
Triepeolus cuckoos tend to run larger than Epeolus. In addition, the apparatus on the tips of the abdomens of Epeolus and Trepeolus differs 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; when sighted, they are usually lurking alone on flowers or in nesting areas frequented by the bees the cuckoos prey on. Both males and females sometimes can be found sleeping in groups in early morning, hanging by their jaws from vegetation visited 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 a female Epeolus abdomen has a characteristic wide patch of silvery hairs.
Distinguishing male Epeolus from male Triepeolus is often far more difficult, even with the aid of a macro lens. For the casual naturalist, the best way to identify males is often to observe their behavior and apprehend them mating with more easily-identified females.
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 such traits as: (1) the colors of various body parts, particularly their 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 traits are also useful for identifying Triepolus species: (1) the time of year in which they fly; (2) (in females), the shape of the bee's abdominal tip, as seen from above and in profile; and (3) (in males) 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 points on the rear edge of the thorax (their length and shape) 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 rufoclypeus
Triepeolus vernus
Triepeolus zacatecus
Dwarf Epeolus Cuckoo Bee
Epeolus pusillus
Family: Apidae
Size: 8-9 mm (female)
Food plant at NBC:
Hierba del marrano
(Symphyotrichum sp.)
Skeleton-leaf goldeneye
(Viguiera stenoloba)
Plant Family: Asteraceae
When seen:
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 is a striking cuckoo bee with violet eyes, red legs and bold black-and-white patterns on its abdomen and thorax.
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 cuckoos 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.
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
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 in the flowers of twisted-rib cactus, a pollinator plant for both of those species.
Food plants at NBC:
Guajillo
(Senegalia berlandieri)
Plant Family: Fabaceae
When and where seen:
May 16, 2021
La Puerta Tract NWR
(Starr County)
Zacatec Triepeolus
Triepeolus zacatecus
Family: Apidae
Size: 15-17 mm (female & male)
A male Triepeolus zacatecus
A male Triepeolus zacatecus: this is a very large cuckoo bee, measuring 17-18 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 thorax of Triepeolus zacatecus has long axillae that are sharply incurved at the tips; and the bee’s protonal collar is wide and protuberant.
Lateral view of head and thorax of male bee: bee’s mesepisternum (on the sides of the thorax) is densely covered with short, pale hairs.
Face of male bee
Triepeolus zacatecus is a Mexican and Central American species that sometimes ranges into the United States. It uncommon in the Lower Rio Grande Valley. Its distribution is centered in Mexico. The bee shown here appeared in May 2021 just a few miles from the Mexican border.
Triepeolus zacatecus is an exceptionally large cuckoo bee whose body and legs are covered with patterns formed by appressed (very short), pale hairs. The hairs on its abdomen are distinctly yellowish. The bee's tegulae are black and its wings smoky and dark-veined. The bee’s face is almost entirely dark, with some faint reddish coloration on the mandibles.
This cuckoo bee's size makes it stand out in the field. Triepeolus zacatecus is similar to the equally large species Triepeolus grandis. The latter, however, usually has more extensive reddish coloration. It ranges farther northword than Triepeolus zacatecus, from from central Mexico to Oklahoma, and it is more common in the United States.
The host species of Triepeolus zacatecus remains unknown. The similar Triepeolus grandis is known to prey on large Diphaglossinae such as Ptilosglossa. The Mexican feather-tongued bee (Ptiloglossa mexicana) occurs in the immediate area in which the male Triepeolus zacatecus shown here was found.
Food plants at NBC:
Blanket flower
(Gaillardia pulchella)
Wild sunflower
(Helianthus)
Skeleton-leaf goldeneye
(Viguiera stenoloba)Plant
Seaside goldenrod
Solidago sempervirens:
Plant Family: Asteraceae
When seen:
November 2018
October-November, 2019
Red-faced triepeolus
Triepeolus rufoclypeus
Family: Andrenidae
Size: 13 mm (male)
A female Triepeolus rufoclypeus
Dorsal view of a female Triepeolus rufoclypeus
Close-up of bee's thorax (scutum and scutellum)
A female Triepeolus rufoclypeus
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.
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].