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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

Epeolus pusillus cuckoo bee - (c) Copyright 2018 Paula Sharp
Epeolus pusillus cuckoo bee - (c) Copyright 2018 Paula Sharp

A female  dwarf Epeolus cuckoo hanging by its jaws



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

Epeolus pusillus

A violet-eyed female dwarf Epeolus  (Epeolus pusillus) 

Epeolus pusillus cuckoo bee - (c) 2018 Paula Sharp

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.



Mission, Texas

Epeolus pusillus, Triepeolus rufoclypeus, cuckoo bee, Triepeolus, Epeolus

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

Triepeolus vernus cuckoo bee - (c) Copyright 2019 Paula Sharp

A female spring Triepeolus

Triepeolus vernus cuckoo bee - (C) Copyright 2019 Paula Sharp

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: 

(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

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

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)

Triepeolus rufoclypeus - (c) Copyright 2019 Paula Sharp

A female Triepeolus rufoclypeus

Triepeolus rufoclypeus - (c) Copyright 2019 Paula Sharp

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,  Accessed [day/month/year guide accessed].

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