THE BEE TRIBE EXOMOLOPSINI
Genus Exomolopsis

Genus Anthophorula

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The bee tribe Exomalopsini contains two genera of similar bees:  Exomalopsis and Anthophorula.

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GENUS EXOMALOPSIS:  THE NOT-SO-UGLY BEE 
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If you live in more northern parts of the United States, you may never have had the pleasure of encountering an Exomalopsis.  These are beautiful bees. They are uniquely colorful:  their legs may be rust-orange or multi-colored, and their eyes are brilliant green or blue-gray. Their abdomens are dark and ringed with pale hairs.  Females have luxuriant scopal hairs on their hind legs evocative of the groomed fur of champion show dogs.  Males tend to have very long antennae, and  partly-yellow jaws.  Exomalopsis bees are frequent visitors to the National Butterfly Center during the fall.

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These bees deserve a name that reflects their elegant beauty.  Nonetheless, they instead bear the hefty label “Exomalopsis”.  In Greek, Exomalopsis literally means “not bad-looking”.   (Exo= without; mal=bad; opsis=appearance).  Thus, loosely translated, one might call the Exomalopsis the "Not-so-ugly Bee".  

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GENUS ANTHOPHORULA:  THE SMALLER COUSIN

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Anthophorula bees, close cousins in the Exomalopsini tribe, greatly resemble Exomalopsis bees.  Anthophorula is a genus of furry bees that often have dark abdomens banded with pale hairs.  Female Anthophorula have luxuriant scopal hairs on their back legs.  Males sport long antennae and often have yellow facial markings. 

 

As a rule, Anthophorula bees tend to run smaller than Exomalopsis bees.  (In Greek, the name Anthophorula means "little flower bearer".)  Anthophorula bees tend to appear at the National Butterfly Center in early spring, shortly before prickly pear cactus begins blooming in Hidalgo County.

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Anthophora vs. Exomalopsis

 

Exomalopsis and Anthophorula bees share a trait that the legendary entomologist, Charles D. Michener, noted was common to all members of the tribe Exomalopsini:  they have a long row of erect, well-separated hairs lining the inner side of each compound eye orbit.   

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Other minute differences, shown in the photo strip at right, separate these two genera.  According to entomologist Charles D. Michener:  (1) The clypeus (the face part above the jaws) of the male Exomalopsis is always dark. The Anthophorula male’s clypeus, however, may be yellow.  (2)   The hind knee plates are larger on Exomalopsis males than on Anthophorula males. (2) The stigma of the wing is proportionately larger in Exomalopsis; in Anthophorula, the stigma is less than half the length of the marginal cell, with some exceptions. (A few species of Anthophorula also have two marginal cells instead of three.)  

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Exomalopsis and Anthophorula behavior

 

Both Exomalopsis and Anthophorula bees are solitary and nest in the ground.  In both genera, each female bee provisions her own individual nest, digging out oval egg chambers and coating them with a thin waterproof lining.  Females store pollen for offspring on a “foot,” a small mound of dirt slightly elevated from the nest floor, to protect against moisture.  

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Despite their solitary status, Exomalopsis and Anthophorula bees may live communally, with several females inhabiting a single burrow that shares a common entrance.  Within at least one Exomalopsis species, E. solani, females even aid one another in storing pollen.  Such behavior is relatively rare among bees. 

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Pollinator plants

 

Many Exomalopsis bees are pollinator generalists. At the NBC, Exomalopsis bees are frequent visitors to an array of wild and garden flowers, most notably skeleton-leaf goldeneye, crucita, croton and mallows.  

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Anthophorula bees are also often generalist pollinators; some, however, specialize in pollinating such plants as gumweed and leafy spurge, while others exhibit a preference for plants in the aster and buckwheat families.   The Anthophorula compactula shown below has appeared nearly exclusively on prickly pear cactus, twisted rib cactus and red prickly poppy at the National Butterfly Center and surrounding areas.  Nonetheless, this species is known to visit a wide gamut of plants.  

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Some Exomalopsis and Anthophorula bees are capable of buzz pollination and are thus good pollinators of crops in the tomato family (Solanaceae).  Plants in this family, which includes peppers, eggplants and potatoes, require this special pollination method (in which the bee vibrates its wing muscles to shake pollen loose from a flower's anthers).  This capability is an important trait, because honey bees cannot buzz pollinate and thus cannot used to pollinate such crops.  At the National Butterfly Center, Exomalopsis bees can be observed visiting the wildflower silver-leaf nightshade, a member of the Solonaceae family. 

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Species range and Identification information: 

 

Both Exomalopsis and Anthophorula bees are found only in the Western Hemisphere. Ten species of  Exomalopsis inhabit the United States.  At least 7  have been documented previously in Texas:  Exomalopsis analis, E. birkmanni, E. mellipes,  E. snowi, E. solani, E. solidagnis and E. tibialis. 

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There are approximately 40 species of Anthophorula in the United States.  Most of these are found in California or the southwest, although one species of Anthophorula,  A. pygmaeia, occurs throughout most of the U. S.  At least 14 Anthophorula species have been documented in Texas or along the Texas-Mexico border:  Anthophorula asteris, A. compactula, A. completa, A. consobrina, A. ignota, A. interrupta, A. lacticincta, A. micheneri, A. morgani,  A. nitens, A. parva, A. pygmaea, A. sidae and A. texana. 

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Little photographic documentation of Exomalopsis and Anthophorula species is available on the Internet, and thus identifying them can be challenging for naturalists and pollinator enthusiasts. The Exomalopsis and Anthophorula species shown here were identified through the aid of Texas bee expert Jack Neff, President of the Central Texas Melittological Institute.  Explanations of distinguishing traits of individual  Exomalopsis and Anthophorula species found at the NBC are given below, together with detailed photographs.