NOMIA  &  DIEUNOMIA 

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Nomia and Dieunomia are two genera of ground-nesting bees that belong to the subfamily Nomiinae of the  sweat bee family Halictidae.  Bees of the genus Nomia inhabit North America, Africa, Australia and Asia.  Bees of the genus Dienomia are found only in the New World. 

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NOMIA  BEES
Genus Nomia

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Bees of the genus Nomia belong to the family Halictidae, which also includes the green and dark sweat bees shown in the next two sections of this guide.  North American Nomia, however, tend to be larger than their cousins in those groups:  the typical Texan Nomia is medium-sized, i. e., around the size of a honey bee or slightly smaller.

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Nomia bees found in North America are dark-bodied, with abdomens that are sometimes girded by striking pearlescent  bands.  The faces of Nomia bees are distinctive:  they are round and somewhat eerie, with eyes that seem to meld into the bottom edge of the bee's clypeus (the face-part above the jaws).  The bees' antennae are set near the middle of the face.

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The best known member of this genus within the United States is the alkali bee (Nomia melanderi).  Found in the western United States, this Nomia thrives in soils that are salty or heavily alkaline and has proven instrumental in the pollination of alfalfa.  

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The Four-Banded Nomia or Pearly-banded Bee

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Less well-known is the four-banded Nomia (Nomia tetrazonata), also called the pearly-banded bee.  

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At the National Butterfly Center, male four-banded Nomia bees emerge in spring in large numbers to feed on native Berlandier’s fiddlewood, a plant in the verbena family adorned with clusters of small white flowers.  These bees are common throughout Hidalgo County from late March through late May, particularly where this plant is well- established. 

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Four-banded Nomia bees are striking:  the bands on the bees' abdomens iridesce in sunlight, appearing at times blue and at other times yellow or pale orange, depending on the angle and quality of light hitting them.  This effect is produced by light diffraction and interference caused by surface structures on the bees’ abdomens.

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Within North America, this beautiful bee is found in the western United States, as far north as Oregon and as far east as eastern Texas; and in the northern half of Mexico. ​ Nomia tetrazonata has been documented on flora from a wide range of families, including, for example, salvias, mallows, legumes, asters, creosote, mesquite and tomato-family plants.

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Bee Behavior

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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 photographs on this page, male bees have enlarged leg segments fringed with long hairs, attributes used to subdue females during mating.

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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.  

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Many Nomia species, including the alkali bee, are solitary, with each bee constructing its own individual nest. Four-banded Nomia bees, however,  live communally, with up to 20  bees sharing a single nest.  Four-banded Nomia bees' 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 bees are sometimes invaded by the cuckoo bee species Triepeolus verbesinae.

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Species Identification of Nomia bees

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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 they are enlarged, and by their color.  The hind-leg tibias of male Nomia tetrozonata, for example, have pale-gold areas that expand above the leg spurs in a roughly triangular shape, as shown in the photographs below. The tibias of alkali bees (Nomia melanderi) are even more enlarged.  One Texas species, Nomia nortoni, has grossly dilated tibias clearly visible to the naked eye.

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DIEUNOMIA  BEES

Genus Dieunomia

 

Dieunomia, like Nomia bees, belong to the bee tribe Nomini of  the sweat bee subfamily Nomiinae.  Dieunomia range greatly in size, from as large as 23 mm, to as small as 7 mm -- like the Nevada Dieunomia shown at right and below. Dieunomia are solitary bees, each building its own 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 on 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.  In addition, on Dieunomia, the same segments tend to have some kind of pitting, while on Nomia, the segments lack pits. 

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Female Dieunomia have long scopal hairs (on their second through fifth 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 roundish in shape, with eyes that seem to meld with the clypeus -- like the face of the Nomia bee shown avoe on this page.

 

As noted above, Dieunomia are found only in the New World.  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 Nevada Dieunomia bee shown on this page is a member of the subgenus Epinomia.

 

Nevada Dieunomia bees have been separated into subspecies: Dieunomia nevadensis bakeri, shown here, has a generally black body and red legs, while Dieunomia nevadensis arizonensis has red on its thorax and abdomen (as well as its legs).