SHARP-EATMAN
NATURE
PHOTOGRAPHY
ID GUIDE TO WILD BEES
OF THE NATIONAL BUTTERFLY CENTER
Mission, Texas
DIGGER BEES
Anthophora
DIGGER BEES
Genus Anthophora
Anthophora, commonly called 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 are solitary – that is, each bee builds and provisions its own nest. Nonetheless, digger bees are often gregarious, preferring to construct their nests close by one another, sometimes forming large aggregations that number in the hundreds or even thousands.
As their name suggests, 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 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 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 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 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 their behavior to be remarkable, because solitary bees rarely act collectively in this manner.
Identification information:
Anthophora 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 possess exceptionally long tongues. Females 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 sharp points and edges.
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' mandibles; their clypei and labrums (face parts above and between the mandibles); 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 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 generalist 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.
A male California digger bee (Anthophora californica)
Hind leg of a male California digger bee
A female California digger bee drinking nectar from a flower
A male Anthophora capistrata
TAXONOMY OF ANTHOPHORA DIGGER BEES
Order: Hymenoptera
Family: Apidae
Subfamily: Anthophorinae
Tribe: Anthophorini
Genus: Anthophora
Species shown below:
Anthophora (Anthophoroides) californica
(California digger bee)
Anthophora (Mystacanthophora) capistrata
(Masked salvia digger bee)
Anthophora Species of the National Butterfly Center
Masked salvia 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
Golden dewdrops
(Duranta erecta)
Plant family: Verbenaceae
When seen:
April & October 2019
A male Anthophora capistrata
A male Anthophora capistrata
The male Anthophora capistrata is readily identified by the distinctive black-and-white pattern on the bee's face.
Close-up of mae bee's face
Profile of face
The bee's thorax is covered with mostly light hairs, with some dark hairs mixed in. There are both dark and light hairs on the vertex.
A female Anthophora capistrata on shrubby blue salvia. Female Anthophora capistrata are robustly built.
Frontal view of a female Anthophora capistrata
Females lack the black-and-white mask characteristic of males of this species.
The hairs on the face of the female Anthophora capistrata are hooked at the ends; the female bee uses these hooked hairs to collect pollen from mints.
Note the mixture of light and dark hairs on the female bee's thorax.
A male Anthophora capistrata
A female Anthophora capistrata
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. The female Anthophora capistrata has a black face and lacks the ornate mask of the male bee.
Anthophora capistrata is found primarily in Mexico. Within the United States, this species has been documented for the most part close to the Texas border. 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.
Anthophora capistrata is associated with plants of the mint family (Lamiaceae). The male bee shown here was observed energetically guarding a shrubby blue salvia bush in the third week of April, 2019. 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)
Golden dewdrops
(Duranta erecta)
Plant family: Verbenaceae
Shrubby blue sage
(Salvia ballotiflora)
Plant family: Lamiaceae
Silver-leaf nightshade
(Solanum elaeagnifolium)
Plant family: Solanaceae
Guayacan
(Guaiacum angustifolium)
Plant family: Zygophyllaceae
When seen:
Feb. - Nov. 2018-2020
A male California digger bee inserting its long tongue into a Duranta blossom
Profile of a male California digger bee: digger bee species are distinguished by such minute traits as the coloring and patterns on their mandibles, faces and antennae; the color of their thorax hairs; the presence, width and continuity of hairbands on their abdomens; body length; geographical location; and the plants they visit.
Male California digger bees have light-brown hairs on the thorax and vertex (the space behind the eyes).
Face of a male California digger bee
A female Anthophora californica
The female bee's face, mandibles and antennae are dark.
A female Anthophora californica using her long tongue to drink nectar from Duranta blossoms
The bee's abdomen has bold black and white bands. Its leg and thorax hairs are pale.
A male California digger bee (Anthophora californica)
A male California digger bee
A female California digger bee
A female California digger bee
CITE THIS PAGE: Sharp, Paula and Ross Eatman. "Anthophora." Wild Bees of the National Butterfly Center of Mission, Texas. 15 Jan. 2019, http://www.wildbeestexas.com. Accessed [day/month/year guide accessed].