EPEOLUS AND TRIEPEOLUS CUCKOO BEES
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.
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 nodes where the wing meets the body). Others, like the dwarf Epeolus shown here, have exquisitely-colored eyes.
Epeolus cuckoo bees usually parasitize the nests of cellophane bees of the genus Colletes (shown on the previous page of this guide). Cellophane bees protect their nests from moisture by lining their brood-cell walls with a plastic-like substance. The female Epeolus bee 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 bee 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 cuckoo bees 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 apparati on the tips of Triepeolus and Epeolus females' abdomens differ in ways that reflect the characteristics of the nests each cuckoo genus parasitizes. Rather than sporting saw-like tools on their abdomens like Epeolus bees, 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 at the National Butterfly Center
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 in areas frequented by the bees the cuckoos prey on.
At the National Butterfly Center, Epeolus cuckoos can be found visiting aster-family plants during November. The most common of these is the Epeolus pusillus cuckoo 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 cuckoos also have been documented parasitizing the nests of Colletes americanus, C. ciliatoides and C. deserticola.
Triepeolus rufoclypeus cuckoo bees appear in relatively large numbers at the National Butterfly Center in early fall. They tend to appear on creeping vervain, and on sunflowers and other members of the aster family, plants frequented by various long-horned bee species during the same period.
Triepeolus vernus appears in April during the spring cactus bloom in Hidalgo County, and is the single cuckoo bee this website's author have identified vivisting prickly pear cactus.
Distinguishing Epeolus from Triepeolus
Triepeolus and Epeolus bees can be tricky to tell from one another. As noted, Triepolus bees are generally larger. The minute differences in the weaponry on the abdomen tips of female Epeolus and Triepolus 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 photostrip at right, the tip of a female Epeolus bee's 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 identifying males is often to observe their behavior and apprehend them mating with more easily-identified females.
Identifying Triepeolus and Epeolus species
Triepeolus species are also sometimes difficult to differentiate from one another and may require expert assistance to identify. Triepeolus bees are distinguished in part by: (1) where they are found and when they fly; (2) the patterns on their thoraxes and abdomens, which are formed by short, appressed, pale hairs; (3) the color of their legs, tegulae (wing nodes), face-parts, jaws and antennal segments ; (4) (in females) the shape of the bee's abdominal tip, as seen from above and in profile; and (7) (in males) by characteristics of the clypeus (the face part above the jaws).
A highly useful guide for identifying Triepeolus species is Molly Rightmyer's definitive and comprehensive work, “A review of the cleptoparasitic bee genus Triepeolus," noted in this guide's reference page. Many Triepeolus species in the valley, however, remain undocumented.
Epeolus species are differentiated by many of the same traits used to identify Triepeolus bees -- among them, the patterns on the bees' thoraxes and abdomens, and the colors of various body parts. In addition, traits of the scutellum (hindmost portion on the bee's thorax) 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, length or position may be distinctive of a particular species; the shape of the scutellum's hind edge also aids in identification.
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, also noted in this guide's reference page.
A female Epeolus cuckoo bee
A male Triepeolus cuckoo bee
Traits of Epeolus and Triepeolus bees
A female dwarf Epeolus cuckoo hanging by her jaws
TAXONOMY OF EPEOLUS AND
AND TRIEPEOLUS BEES
Genus: Epeolus and Triepeolus
Species shown below on this page:
Dwarf Epeolus Cuckoo Bee
Size: 8-9 mm (female)
Food plant at NBC:
Hierba del marrano
Plant Family: Asteraceae
A violet-eyed female dwarf Epeolus (Epeolus pusillus) cuckoo bee
A female dwarf Epeolus cuckoo bee
Spring Triepeolus Cuckoo Bee
Size: 7-10 mm (female)
Food plants at NBC:
Texas Prickly Pear
Twisted rib cactus
Plant family Cactaceae
A female spring Triepeolus
A female Triepeolus vernus
This small, beautiful cuckoo bee is found only in southern Texas, and emerges for only a brief period, from March through April. Little research exists on this species, and the hosts of Triepeolus vernus remain unknown. The bee shown here was found patrolling the ground in an area where the little pricky pear long-horned bee (Melissodes opuntiellus) and the compact Anthophorula (Anthophorula compactula) were nesting. The flight season of these species coincides with that of Triepolus vernus, and all three bees visit Texas prickly pear. Further research might succeed in linking Triepeolus vernus with one of these hosts.
Food plants at NBC:
Plant Family: Asteraceae
Size: 13 mm (male)
A female Triepeolus rufoclypeus
A female Triepeolus rufoclypeus