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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 brood parasites or cleptoparasites.

Cuckoo bees drink nectar from flowers, and they often appear on the very blossoming plants that their hosts prefer.  Cuckoo bees, however, do not gather pollen from flowers.   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. 


Cuckoo bees 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, or lurking outside of nests, waiting for the opportunity to enter them.  

WIthin the United States, the tribe Epeolini contains two varieties of cuckoo bee -- Epeolus and Triepeolus.  Bees in these two genera usually have well-defined white or yellow bands on their abdomens and often sport bold black-and pale 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 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 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.  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 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 penicilliferus

   Triepeolus rufoclypeus

   Triepeolus vernus

   Triepeolus zacatecus


Mission, Texas

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

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.)

(Viguiera stenoloba)
Plant Family:  Asteraceae

When seen at the NBC:

November 2018
April 2019

Epeolus pusillus; Copyright 2021 Paula Sharp

A violet-eyed female dwarf Epeolus  (Epeolus pusillus) 

Epeolus pusillus; (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.


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)

Triepeolus zacatecus; Copyright 2023 Paula Sharp

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.  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.  Triepeolus grandis is more common within the United States and ranges farther northword than Triepeolus zacatecus, from from central Mexico to Oklahoma.

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:

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)

Triepeolus pencilliferus; Copyright 2023 Paula Sharp

A male Triepeolus penicilliferus 

Male bee

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

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 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)

(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)

Female bee

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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