ID GUIDE TO WILD BEES
OF THE NATIONAL BUTTERFLY CENTER
Mission, Texas

DIGGER BEES

Anthophora

DIGGER BEES
Genus Anthophora

Anthophora digger bees are entertaining, unusually noisy insects with a distinctive way of flying. They zip speedily around flowers and then stop abruptly, hovering in front of a blossom, sometimes angling their long tongues down a flower’s throat without letting their feet touch the petals.  Or they buzz raucously while clinging to the flowers, and thrust their faces so deeply into them that when the bees emerge, their heads and thoraxes are coated in pollen.

Anthophora digger bees are solitary – that is, each bee builds and provisions its own nest.  Nonetheless, female Anthophora digger bees are often gregarious, preferring to build their nests close by one another, sometimes forming large aggregations that number in the hundreds or even thousands.  

 

As their name suggests, Anthophora digger bees typically nest in the earth, either in level ground or vertical banks.  A few Anthophora species make tunnels in pithy stems and rotted wood, lining their nests with oils collected from plants. 

Female Anthophora digger bees construct ground nests by digging with their front legs and using their mandibles to loosen dirt.  In some species, such as Anthophora abrupta, females use their front legs to haul mud through the air; they then work the mud to moisten the dirt of dry nesting areas, softening it up for better digging. 

 

When expanding underground lairs, some Anthophora females pile excavated soil outside their holes in tall thin stacks called tumuli. Female Anthophora may vigorously defend their nests against predators:  Anthophora females have been observed dragging parasitic bees bodily from nest holes.

Male digger bees, like the Anthophora californica shown here, may have thickly-built hind legs equipped with wide blades.  Such leg modifications are used for grasping female bees during mating. Male Anthophora bees often gather outside of nest tunnels dug by females.  The males sometimes pile together in scrums outside of nest entrances, awaiting the emergence of a female.  When she appears, they jump on her en masse.

Various species of Anthophora digger bees have been documented engaging in boisterous behavior.  In 1929, the entomologist Phil Rau wrote of Anthophora abrupta: “They are neither timid nor aggressive, but …how conspicuous they are as they noisily swing their ponderous bodies to and fro on the wing, arrive home and scramble into their burrows or come tumbling out headlong and dash off into the sunny fields, with all the exuberance of boys just out of school. They have none of the shy, stealthy ways of maneuvering, whereby some of the smaller and daintier varieties of bees and wasps hold their own in a competitive world.”

Entomologist Robbin Thorp recorded in 1969 that if one strolled through a nest colony of Anthophora  edwardsi,  "swinging an insect net about a meter above the ground, the females would aggregate in the plane of motion.  Thus it was possible to capture 25 to 50 females in five sweeps".  Thorp noted also that objects thrown over or onto the nesting site were likely to be followed aggressively by large numbers of females.  He found this  behavior to be remarkable, because solitary bees rarely act collectively.

Identification information: 

Anthophora digger bees are generally somewhat larger than honey bees and robustly built, with black or black-and-white-striped abdomens and beige or golden-brown thorax hairs.  Because of their hefty builds and black-and-pale coloration, digger bees are sometimes mistaken for bumblebees.  

Both male and female Anthophora digger bees possess exceptionally long tongues.  Female digger bees have shaggy hairs on their back legs, used to carry pollen. As noted, males, such as the California digger bee shown here, may have reddish or ornately sculpted legs with prominent points and sharp edges.  (Not all male digger bees possess this feature.)

 

Male digger bees of many species have pale masks on their faces, as shown in the photographs at right of Anthophora capistrata and Anthophora californica.  Male digger bees'  jaws; their clypeuses and labrums (face parts above and between the jaws); and their scapes (lower antennal segments) may be white, yellow or yellowish-white. Female bees tend to have black faces.  Typically, digger bees have “roman noses” or concave profiles.

Pollination

Female Anthophora digger practice buzz pollination -- that is, they vibrate their wing muscles, shaking pollen from the anthers of flowers.  These bees are exceptionally effective pollinators and play an important role in maintaining wildflower diversity, in part because their long tongues allow them to pollinate deep-throated and tubular blossoms inaccessible to many bees.

Digger bees are generalists pollinators that visit an impressively wide range of plants. Texas species feed on such flora as salvias; cacti and mesquite; verbenas; sunflowers, thistles, goldenrods, and other aster-family plants; melons and squash; roses; vetch; plants of the morning glory family; and evening primrose.

Anthophora californica digger bees appear at NBC in the fall, hovering around pigeonberry and Berlandier’s fiddlewood. These bees also frequent silver-leaf nightshade, a member of the tomato family (Solanaceae) that requires buzz pollination.  Anthophora capistrata bees are documented pollinators of mesquite:  at the NBC, these bees have been found in April and October on blue salvia shrubs and neighboring pigeonberry bushes.

Anthophora californica - (c) Copyright 2019 Paula Sharp

A male California digger bee (Anthophora californica)

Anthophora californica digger bee leg - (c) Copyright 2018 Paula Sharp

Hind leg of a male California digger bee

A female California digger bee drinking nectar from a flower

A male Anthophora capistrata digger bee - (c) Copyrght 2019 Paula Sharp

A male Anthophora capistrata digger bee 

TAXONOMY OF ANTHOPHORA DIGGER  BEES

Order:   Hymenoptera

Family:   Apidae

Subfamily:  Apinae
Tribe:  Anthophorini

Genus:   Anthophora

Species shown below:
  ​    Anthophora (Anthophoroides) californica 

            (California digger bee)

      Anthophora (Mystacanthophora) capistrata

            (Capistrata digger bee)

Anthophora Digger Bee Species of the National Butterfly Center

Capistrata Digger Bee

Anthophora capistrata
Family:  Apidae

Size:  12-13  mm  (male)

           14 mm (female)

Associated plant at NBC: 
Shrubby blue sage

(Salvia ballotiflora)

Plant family:   Lamiaceae

Pigeonberry

Duranta erecta)

Plant family:   Verbenaceae

When seen:
April & October 2019 

A male Anthophora capistrata digger bee - (c) Copyrght 2019 Paula Sharp

A male Anthophora capistrata digger bee 

Male bee: 

Female bee: 

A male Anthophora capistrata digger bee - (c) Copyrght 2019 Paula Sharp

A male Anthophora capistrata digger bee 

Anthophora capistrata digger bee - (c) Copyright 2019 Paula Sharp

A female Anthophora capistrata digger bee 

A note on Anthophora capistrata:  This species was first described by entomologist E.T. Cresson in 1878.  Capistrata means “wearing a headdress” or “wearing a halter,” a reference to the distinctive black-and-white pattern on the male bee's face.

 

Cresson painstakingly described this pattern, a trait that readily identifies the species.  He also noted other traits of the male Anthophora capistrata:  the male bee has black spots on the base of each mandible;  its scapes (bottom segments of the bee's antennae) are white; and the the bee’s head, thorax, first abdominal segment and legs are densely covered with hair.

Cresson based his description of Anthophora capistrata on an examination of two male bees found by Swedish entomologist Gustave W.  Belfrage during collecting expeditions he undertook in Texas in the mid-1880’s.  The female Anthophora capistrata has a black face and lacks the ornate mask of the male bee.

 

The Discover Life Database records that Anthophora capistrata digger bees are found primarily in Mexico.  Within the United States, this species has been documented for the most part close to the Texas border.

Anthophora capistrata digger bees are associated with mesquite.  The Discover Life database records them feeding on salvia as well.  The male bee shown here was observed energetically guarding a shrubby blue salvia bush in the third week of April, 2019.  At the time, honey mesquite trees were in full bloom in the area.  The female bee was discovered in mid-October, feeding on shrubby blue salvia alongside several male bees.

California Digger Bee

Anthophora californica
Family:  Apidae

Size:  12 mm  (male & female)

Associated plants at NBC: 
 

Berlandier's Fiddlewood
(Citharexylum berlandieri)
Pigeonberry

 (Duranta erecta)
Plant family:  Verbenaceae

Shrubby blue sage

(Salvia ballotiflora)

Plant family:   Lamiaceae

Silver-leaf nightshade
(Solanum elaeagnifolium)
Plant family:  Solanaceae

 

When seen:
September 2018 

Male bee: 

Female bee: 

California Digger Bee - Anthophora californica - (c) Copyright 2018 Paula Sharp

A male California digger bee 

Anthophora californica digger bee - (c) Copyright 2018 Paula Sharp

A male California digger bee 

Anthophora californica digger bee - (c) Copyright 2019 Paula Sharp

A female California digger bee 

Anthophora californica digger bee female - (c) Copyright 2019 Paula Sharp

A female California digger bee 

Permissions and Copyright Information:   All images on this site are (c) Copyright 2018-2019 Paula Sharp and Ross Eatman.  All rights reserved. All photographs are protected by registered copyright.  Please contact Sharp-Eatman Nature Photography for written permission before using any of these images for any purpose. 

Last updated November 2019

 1-15-19