Nomia & Dieunomia
Nomia and Dieunomia are two genera of ground-nesting bees that belong to the subfamily Nomiinae, within the sweat bee family Halictidae. Sometimes called "large sweat bees," Nomia and Dieunomia tend to run bigger than the Augochlorini and Halictini sweat bees shown in the preceding sections of this guide.
Nomia inhabit North America, Africa, Australia and Asia. Nomia of North America are dark-bodied, with abdomens that are relatively hairless and often girded by striking pearlescent bands. Males often have enlarged tibiae, used to subdue females during mating.
The faces of Nomia are distinctive: they are somewhat round and a little eerie, with eyes that converge downward, seeming to join seamlessly with the lower face. The typical Texan Nomia is a medium-sized bee, i. e., around the size of a honey bee or slightly smaller.
Species Identification of Nomia
North American Nomia species are differentiated by such traits as the presence and completeness of iridescent bands on the bees' abdomens; the absence or presence of such bands on the first abdominal segment in particular; the pitting on the bees' faces, thoraxes and abdominal segments; and (in males) the color of the bees' antennae.
Males are often identified in part by leg traits. Males' legs differ in the degree to which their hind-leg tibiae are enlarged, and by their color. The hind-leg tibiae of male Nomia tetrazonata, for example, have pale-gold areas that expand above the leg spurs in a roughly triangular shape, as shown in the photographs below. One Texas species, Nomia nortoni, has grossly dilated tibiae clearly visible to the naked eye.
Dieunomia are found only in the New World. They range greatly in size, from as large as 23 mm, to as small as 7 mm. There are at least nine species of Dieunomia in the Americas, and these divide into two subgenera, differentiated roughly by size: larger bees fall into the subgenus Dieunomia, and smaller ones into Epinomia. The Baker's dieunomia shown on this page is a member of the subgenus Epinomia.
Dieunomia are solitary bees, with each female building its own individual nest. Nonetheless, Dieunomia sometimes nest in large aggregations in sandy soil or farmland. Because their nests are deep, they can survive plowing. Dieunomia are pollen specialists of the plant family Asteraceae.
Distinguishing traits of Dieunomia
In The Bees of the World, Charles D. Michener noted these two distinctive traits of Dieunomia: the first segment of the Dieunomia’s abdomen is V-shaped, and it has a concave depression in the middle. Michener also wrote that Dieunomia can be distinguished from Nomia by the fact that Dieunomia have bands of hair on the second through fourth segments of their abdomens, while on Nomia those segments are relatively hairless and have an enamel-like appearance. In addition, on Dieunomia, the same segments tend to have some kind of pitting, while on Nomia, the segments usually lack pits.
Female Dieunomia, in addition to scopal hairs on their hind-leg tibiae, have long scopal hairs under their abdomens (on the second through fifth sternal segments), often clearly visible from the sides as well as from below. Male Dieunomia often have enlarged hind legs; their middle legs may be partly enlarged as well. The faces of Dieunomia are generally similar to those of Nomia - somewhat round, with convergent eyes.
A male four-banded Nomia on Berlandier's fiddlewood
TRAITS OF NOMIINE BEES
This is a male four-banded Nomia. The bee's eyes converge downward and join seamlessly with the lower edge of the clypeus (the face part above the mandibles). The antennae of Nomia are set low on its face.
Similarly, the compound eyes of this Baker's Dieunomia converge downward in its roundish face. Its antennae are low-set, and its compound eyes appear inlaid into the surface of the face.
The abdomen of a four-banded nomia: the bands are pearlescent. This is a trait of several Nomia species of North America.
TAXONOMY OF NOMIA
Species found at NBC:
Nomia tetrazonata uvaldensis
TAXONOMY OF DIEUNOMIA
Species found at NBC:
Dieunomia nevadensis bakeri
Four-banded Nomia Bee
aka Pearly-banded Bee
Nomia tetrazonata uvaldensis
Size: 9 mm - 10 mm (males and females)
Plant family: Verbenaceae
When and where seen:
NBC: March - May 201
Puerto Rico, TX: May, 2021
Rio Grande City, TX: June, 2021
La Puerta Land Tract: May 2021
Falcon State Park: April 2023
This is a male four-banded Nomia, also known as a pearly-banded bee.
A male four-banded Nomia thrusting its head into a Berlandier's fiddlewood blossom: male Nomia tetrazonata have four opalescent bands on the abdomen.
Dorsal view of male bee: the opalescent bands on the abdomens of both males and females are structural (part of the exoskelton), and not formed by hairs.
A female four-banded Nomia
The female Nomia tetrazonata has three opalescent bands (T2, T3 & T4), rather than four -- unlike the male bee.
Close-up of the female's abdomen: both female and male Nomia tetraonata have an additional band formed by pale hairs on the rim of the first segment (T1)
Rear view of the female bee's abdomen
Dorsal view of head and thorax of female bee
A male four-banded nomia (Nomia tetrazonata)
A female four-banded nomia
Male four-banded nomia on Kidneywood
Also known as the pearly-banded bee, the four-banded Nomia (Nomia tetrazonata) is a medium-sized black bee with an abdomen striped by opalescent bands that shimmer blue or yellow-orange in sunlight. Female bees have three pearlescent bands on the abdomen and males four. The lower hind legs of males are enlarged and partly yellowish-brown.
In the Lower Rio Grande Valley, male Nomia tetrazonata uvaldensis appear in April. They often emerge in large groups all at once. This website's authors have encountered April aggregations of male Nomia tetrazonata, numbering in the hundreds, on small-flowered shrubs such as Berlandier's fiddlewood, coma, coyotillo, guayacan, kidneywood, lotebush and Texas hogplum.
Bee Behavior: Entomologist William T. Wcislo has authored and co-authored several studies of this species. According to Wcislo, four-banded nomia males sleep on vegetation near areas where females are nesting; during waking hours, males patrol nesting sites, waiting to pounce on females as they emerge from their ground holes. As shown in the accompanying photographs, males of this species have enlarged leg segments fringed with long hairs, attributes used to subdue females during mating.
All known North American Nomia bees nest in soil, usually in flat ground. Nomia females coat the linings of their egg cells with a waterproof wax-like material. The burrow entrances of some Nomia species are marked with a “tumulus” or turret.
Many Nomia species are solitary. Nomia tetrazonata, however, are known to live communally, with up to 20 bees sharing a single nest. Four-banded nomia nests lack tumuli and turrets at their entrances, but may be impressively deep, running as far beneath the soil as 20 inches (50 cm). The nests of four-banded nomia are sometimes invaded by the cuckoo bee species Triepeolus verbesinae.
Nomia & Dieunomia Species of the National Butterfly Center
Dieunomia nevadensis bakeri is a small, black bee with red legs and tegulae, a dark abdomen banded by pale hairs, and smoky wings that darken toward the outer edges The thoraxes of both females and males are covered with pale hairs, and the bees have a generally hairy appearance.
Dieunomia nevadensis bakeri can be differentiated from similar Dieunomia species in part by size – Baker’s dieunomia are small even for bees of the subgenus Epinomia. The hind tibiae of Baker’s dieunomia are also distinctive. The male’s hind tibiae each have a bump in the middle and a spike on the lower end.
Dieunomia nevadensis bakeri ranges eastward from Texas to Florida and North Carolina, westward as far as Colorado and Wyoming, and northward as far as Illinois. Cockerell and Cresson identified five subspecies of Dieunomia nevadensis, differentiated in part by geography and the colors of their abdomens. The subspecies Dieunomia nevadensis arizonensis occurs in the southwestern and western United States and Mexico, and its range overlaps somewhat with that of Dieunomia nevadesis bakeri. The former is easily distinguished by its extensively red abdomen.
Dieunomia nevadensis bakeri
Size: 9-10 mm (female & male)
Hoary black-foot daisy
Where and when seen:
NBC: October 2019, NBC
Roma, TX: June 12, 2021
A female Baker's dieunomia (Dieunomia nevadenis bakeri)
A female Baker's Dieunomia: the female's legs are red and covered with fine, white hairs.
Dieunomia nevadensis bakeri females have dark, round-ish faces and predominantly red jaws with black bases and tips.
Close-up of face: the apical edge of the female's clypeus is straight. Its low-set antennae are partly red (on the bases and apical ends of the scapes, on the pedicels and on the front surfaces of the flagellum).
A male Baker's dieunomia (Dieunomia nevadensis bakeri)
A male Baker's dieunomia on goldenrod: like the female, the male has red legs and tegulae, and its abdomen is striped with narrow bands of pale hairs.
Face of male bee: the male's face is densely covered with pale hairs, and its compound eyes converge toward the mandibles.
The male's low-set antennae are dark brown. Its mandibles are mostly reddish, with dark areas near the base and at the tips.
CITE THIS PAGE: Sharp, Paula and Ross Eatman. "Nomia and Dieunomia." Wild Bees of the National Butterfly Center of Mission, Texas. 15 Jan. 2019, http://www.wildbeestexas.com. Accessed [day/month/year guide accessed].