A female Centris nitida emerging from her nest in a bamboo cane
A male shining oil-digger bee
The male bee has mandibles that are primarily yellow, with reddish tips that darken toward the point. The labrum (the part between the mandibles) is yellow, and the clypeus (the part above the labrum) is yellow except for dark margins on the top and bottom.
Note that the third segment of each antenna (called F1) is long -- a little longer than the second through fourth (F2, F3 and F4) combined. There are both light and dark hairs behind the antennae.
There is a patch of dark hairs between the male bee's compound eyes: behind this are light hairs that intermingle at the margin with the dark patch.
A male Shining oil-digger bee (Centris nitida)
Associated plant at NBC:
Plant Family: Asteraceae
Shining Oil-digger Bee
Size: 13 mm (males and females)
Until recently, the shining oil-digger bee (Centris nitida) was rarely found north of Mexico. Centris nitida is generally thought of as a neotropical species that typically ranges from the Texas border through Bolivia. (The species has made a recent appearance in southern Florida, where it is considered invasive but apparently harmless.) Centris nitida is now encountered occasionally at the National Butterfly Center. According to Texas bee expert John L. Neff, the bees' appearance signals that Malpighiaceae-family plants are in bloom somewhere in the vicinity.
Female Centris nitida are easily identified by their distinctive pale facial markings. Males can be distinguished from male Centris atripes by examing the bees' middle legs: the male Centris nitida has a fringe of white hairs on the back of each middle-leg tibia.
Centris are difficult to miss. They are hefty black-and-beige bees that buzz loudly as they zoom through gardens at the National Butterfly Center. Fast and adept fliers, they race around bushes, reversing direction suddenly in order to guard their territories, or diving into flowers to extract nectar, pollen or oil.
Centris are sometimes referred to in popular literature as “oil-digger bees," because many members of the genus extract flower oils from plants. The bees modify and use the oils to line their nest chambers.
A seminal 1981 study of oil-collecting bees by John L. Neff and Beryl Simpson described the front and middle legs of most female Centris as outfitted with small bristle-like hairs called setae, which form combs (made up of narrow lines of setae) and pads (made up of branched and hooked setae). Some of the setae are blade-like and used to cut open flower receptacles that contain oils.
The Centris female’s hind legs are covered with bushy pollen-collecting hairs that are sometimes described as looking like “pantaloons”. Centris females transfer the oils from their front and middle oil-collecting legs to their hind-leg scopal hairs in mid-flight, for transport back to their nests.
Most Centris in the Valley nest in the earth, sometimes near the banks of streams or other bodies of water. They are solitary bees that frequently form aggregations at nest sites. Some Centris species, such as Centris nitida, nest in wood or cavities found in trees. Centris nests tend to be built in irregular clumps of cells, rather than in series.
Centris are associated with plants that produce abundant floral oils, such as manzanita, creosote, and Krameria. Almost all female Centris collect oils, at least at times, from plants in the family Malpighiaceae – which includes such flora as Barbados cherry (Malphigia glabra), a plant native to Hidalgo County. Barbados cherry bushes bloom in the spring at the National Butterfly Center -- when they do, they are mobbed by such large numbers of oil-digger bees that the bushes seem to hum.
Centris also can be observed visiting a range of other plants for pollen or nectar. At the National Butterfly Center, oil-digger bees feed on crucita, mallows, palo verde, golden dewdrops, sunflowers and snoutbean.
A female black-footed oil-digger bee (Centris atripes)
COMPARISON OF CENTRIS & ANTHOPHORA FACES
This is a female Centris nitida: in Texas, both male and female Centris have pale (or sometimes red) markings on their faces.
A male Centris nitida: differences in facial markings help differentiate males and females within a species from each other.
Face of a female Centris atripes: facial markings are also used to distinguish one Centris species from another.
This is a male Centris atripes: its markings differ both from those of the female Centris atripes (which has black on the upper clypeus), and from those of the male Centris nitida (which has black areas on the upper and lower clypeal margins and partly-yellow mandibles).
This is a female Anthophora capistrata. Female Anthophora found in Texas have dark faces, without pale markings -- this trait distinguishes them from Centris females.
This is a male Anthophora capistrata. The singular markings on its face distinguish it from other males with facial markings -- including both other male Anthophora and other male Centris.
Centris occur only in the New World; most are found in Mexico and Central and South America. Most Texas Centris are fairly large (around ½ inch or longer), with black abdomens covered with black hairs; shaggy black legs; thoraxes covered with light-brown or rust-colored hairs; and black heads with green eyes. Both female and male Centris of Texas tend to have pale facial markings -- usually ivory or yellow. This trait helps distinguish them from Anthophora digger bees (shown in this guide's preceding section): in the genus Anthophora, only males have pale marks on their faces.
At least nine different Centris species inhabit Texas:
Centris aterrima, C. atripes, C. caesalpiniae, C. cockerelli, C. hoffmanseggiae, C. lanosa, C. mexicana, C. nitida and C. rhodopus. Two of these, Centris atripes and Centris nitida, have been found at the National Butterfly Center. Although yet undocumented, it is likely that at least some of the other Texas species occur in the Valley.
Centris aterrima is covered almost entirely with black hairs. Centris mexicana sometimes has bright rust-orange hair on its thorax. Centris caesalpiniae and C. rhodopus females have bright red eyes and red on the clypeus, mandibles and legs; males of these species have green eyes and predominantly yellow facial markings and legs. Centris hoffmanseggiae has beige or rust-colored thorax hairs; an abdomen banded by pale hairs; and blue-gray eyes. Female Centris cockerelli have blue eyes and sometimes have a reddish clypeus.
TAXONOMY OF CENTRIS BEES
Species shown below:
Centris (Paracentris) atripes (Black-footed oil-digger bee)
Centris (Hemisiella) nitida (Shining oil-digger bee)
Centris Species of the National Butterfly Center
Black-footed Oil-digger Bee
Size: 15-17 mm (males and females)
Associated flora at NBC:
Plant Family: Verbenaceae
Texas snout bean
(Rhynchosia senna var. texana)
Plant Family: Fabaceae
Big berry manzanita
Plant family: Ericaceae
Plant family: Malpighiaceae
Plant family: Bignoniaceae
April -May 2019
A female Centris atripes: this is a hefty bee measuring 17 mm (about 2/3"). The relative size of the bee can be an important factor that aids in differentiating one Centris species from another.
Female black-footed oil-digger bees have pale hairs on the thorax and vertex (the top of the head). They have dark hairs on all terga (the segments of the upper abdomen).
A male black-footed digger bee: males generally resemble females, but are somewhat smaller. The hairs on the males' middle and hind legs are entirely black.
A male black-footed digger bee emerging from an esperanza blossom: this male spent the night sleeping in an esperanza blossom and buzzed in and out of experanza flowers during the day.
A female black-footed oil-digger bee (Centris atripes)
A male black-footed oil-digger bee
The black-footed oil digger bee (Centris atripes) is a common visitor to the National Butterfly Center in April and May, the months when manzanita and barbados cherry are flowering. Males of this species tend to buzz around the trumpet-shaped blossoms of the ornamental shrub known as esperanza; males sometimes can be found sleeping in esperanza blossoms. Centris atripes nests have been sighted in NBC areas bordering a canal that parallels the Rio Grande.
CITE THIS PAGE: Sharp, Paula and Ross Eatman. "Centris." Wild Bees of the National Butterfly Center of Mission, Texas. 15 Jan. 2019, http://www.wildbeestexas.com. Accessed [day/month/year guide accessed].