SHARP-EATMAN
NATURE
PHOTOGRAPHY
ID GUIDE TO WILD BEES
OF THE NATIONAL BUTTERFLY CENTER
Mission, Texas
ROTUND RESIN BEES
Anthidiellum
ROTUND RESIN BEES
Tribe Anthidiini - Genus Anthidiellum
Anthidiellum of the United States are small, robust bees with relatively hairless, coarsely-pitted bodies. They are usually black with brightly-colored yellow or red markings.
Anthidiellum are rarely reported in the Lower Rio Grande Valley. The bees shown here are the first of the genus Anthidiellum ever reported in Starr County. They belong to the subspecies Anthidiellum notatum gilense -- a subspecies never documented previously in Texas. All appeared in Falcon State Park in April 2023. Among them was an unusual red variant of that subspecies, shown in the first entry below.
Female Anthidiellum of North America construct their nests above ground and in the open. Their nests are made of resin and consist of single isolated cells, or groups of cells, which the bees attach to stems, leaves and rocks.
Distinguishing traits of the genus Anthidiellum
Traits that aid in distinguishing bees of the genus Anthidiellum are shown in the accompanying photo strip. Most notably, an Anthidiellum can be identified by any of these traits: (1) The sutures (seams) under the bee's antennae curve strongly outward; (2) the bee's scutellum (second thorax segment) extends backward like a shelf, overhanging the body behind it; (3) the mesipisternum (the side of the thorax) is divided into a pitted front face and a coarsely-sculptured back face.
Like other members of the family Megachilidae shown in this guide, Anthidiellum have forewings with two submarginal cells, and their tarsi (feet) have arolia.
Anthidiellum species and subspecies
Early texts on North American Anthidiellum species separated them largely by geography and color -- although within a given species, individual specimens often show significant color variation. Other traits used to distinguish Anthidiellum species include the shape of the clypeus (the face-part above the mandibles); characteristics of the tip of the abdomen; traits of the bees' genitalia; and the length of the hairs on males' forelegs.
Anthidiellum occur throughout the world; they are represented by more than 60 species divided into 7 subgenera. In North America, however, there are only a handful of Anthidiellum species, all belonging to the genus Loyolanthidium. The three most common North American species are Anthidiellum notatum, A. perplexum, and A. ehrhorni. Only the first of these appears in Texas.
The species Anthidiellum notatum is currently divided into 5 subspecies. During different periods of taxonomic history, some of these subspecies have acquired species status, and arguably most of them should. The differences among these subspecies are set forth in the second guide entry below.
The last reliable records of Anthidiellum anywhere in the Lower Rio Grande Valley are more than 70 years old: they consist of reports from 1940 and 1951 noting finds of the subspecies Anthidiellum notatum boreale in Cameron County.
A male Anthidiellum notatum gilense
TRAITS OF ANTHIDIELLUM - ROTUND-RESIN BEES
Anthidiellum are robust bees that are usually black with yellow or red markings. Their legs may be black or red, sometimes with yellow markings.
The sutures (seams) under the antennae of Anthidiellum are curved.
Rather than forming a rounded curve, the back of the bee's head has a sharp edge that descends in a vertical face. On Anthidiellum of North America, the back of the head is usually rimmed with with a broad yellow (or red) band.
TAXONOMY OF ANTHIDIELLUM (ROTUND-RESIN BEES)
Order: Hymenoptera
Family: Megachilidae
Subfamily: Megachilinae
Tribe: Anthidiini
Genus: Anthidiellum
Species shown on this page:
Anthidiellum (Loyolanthidium) notatum gilense
Anthidiellum Species of the Lower Rio Grand Valley
Gila rotund-resin bee
(red variant of this subspecies)
Anthidieullum notatum gilense
Family: Apidae
Size: 8-10 mm (red variant male)
Associated plants:
Vara dulce (Rio Grande beebrush)
(Aloysia macrostachya)
Plant family: Verbenacea
When and where seen:
April 19 & 21, 2023
Falcon State Park
(Starr Co.)
Male Anthidieullum notatum gilense (red variant)
A red variation of the male Anthidiellum notatum gilense
The bee has extensive red coloration on its thorax, legs, upper abdomen and sternum.
Alternate view of bee: note that all of the bee's legs are red with yellow markings.
In this red variation, the bee's thorax is red laterally (on the mesipisternum).
The male bee shown here appeared in April 2023 at Falcon State Park. It is an unusual variation of Anthidiellum notatum gilense. It is slightly larger and more extensively red than the typical member of this subspecies. The male bee's legs, the sides of its thorax, and some of the spots on its abdomen are red. A second red-variantmale bee with identical characteristics appeared two days later in the same location.
Examples of a more typical male and female Anthidiellum notatum gilense are shown in the entry below. These bees and the variant shown here were found feeding together on the same vara dulce bush.
Gila rotund-resin bee
(typical bee of this subspecies)
Anthidieullum notatum gilense
Family: Apidae
Size: 8-10 mm (male)
8-10 mm (female)
Associated plants:
Vara dulce (Rio Grande beebrush)
(Aloysia macrostachya)
Plant family: Verbenacea
When and where seen:
April 19 & 21, 2023
Falcon State Park
(Starr Co.)
Male Anthidieullum notatum gilense (typical coloration)
A male Anthidiellum notatum gilense: male bees of this subspecies typically have red legs, with some yellow markings. (Most other subspecies of Anthidiellum notatum have predominantly black legs).
This is the typical form for the subspecies -- although the bee's legs are mostly red, its body lacks the extensive red coloration of the red variant show above on this guide page.
Additional view of the male Anthidiellum notatum gilense: note that (unlike on the red variant), the bee's thorax is black laterally (on the mesipisternum).
Face of male bee: a yellow mask covers the lower half of the bee's face. The mask is brownish between the antennal sockets.
A female Anthidielleum notatum gilelnse: females of this subspecies have predominantly red legs, with small yellow markings.
Alternate view of female bee
Face of female bee: the female's yellow facial markings are less extensive than those of the male bee.
The markings on the female bee's vertex and thorax are similar to the those of the male.
Female Anthidieullum notatum gilense (typical coloration)
Anthidiellum notatum subspecies
Anthidiellum notatum is subdivided into 5 subspecies, which are distinguished largely by geography and color – although the colors of individuals within each subspecies vary significantly. There are also some structural differences among the subspecies. Current taxonomical trends suggest that many of these subspecies will be reclassified as species in their own right.
(1) The nominate subspecies, Anthidiellum notatum notatum, is largely black, with mostly yellow markings on the scutum and abdomen. It sometimes has reddish-brown markings on these areas. On males, T6 is almost entirely black except at the very tip. The femurs of the male’s legs are mostly black. This subspecies is relatively small, measuring 6-7 mm. It is found from the Midwest to the east coast.
(2) Anthidiellum notatum gilense, shown here, has red legs and is found primarily in Arizona, New Mexico and Texas. This is the first record of its appearance in the Lower Rio Grande Valley. The typical bee of this subspecies has a black head and body, and lemon-yellow markings on the thorax, abdomen and tibiae. I ts front femurs are usually black. The female has pale-yellow facial markings, and the male has an extensive pale-yellow facial mask. Typically, the abdomen of this subspecies has an oblong yellow spot on either side of T1. The bees featured here, as noted, include a variation with much more extensive red markings. Anthidiellum of this subspecies are relatively large (8-10 mm).
(3) Anthidiellum notatum boreale has nearly the same color pattern as A. notatum notatum, with these differenes: the female’s clypeus is black; and the axillae are almost entirely black. Additionally, the area between the female’s ocelli is nearly flat, with a few scattered pits. The male’s abdomen has a median longitudinal ridge on the last two tergal segments. This subspecies ranges from Nebraska to Iowa, Indiana and Illinois. There are 1940 and 1953 reports of this subspecies in Cameron County, Texas.
(4) Anthidiellum notatum robertsoni has extensive yellow coloration, tends to run smaller than the other subspecies. The abdomens of males have a longitudinal ridge on the last two tergal segments. T6 of the male has a black spot that looks like an inverted T. The male's legs are black, with yellow markings of varying sizes on the tibiae and the basitarsi. On females, the clypeus is entirely black; and the female's legs have yellow markings on the front and middle tibiae, and sometimes on the hind tibiae. The female’s rearmost abdominal segment (T6) usually has two x-shaped yellow spots. This subspecies lacks the brownish markings sometimes found on Anthidiellum notatum notatum. This subspecies typically ranges from California and Oregon to Colorado. It has been reported in Texas north of the Valley.
(5) Anthidiellum notatum rufimaculatum is endemic to Florida. It is a partly-black bee with extensive reddish markings: on males, the legs (the tibiae, tarsi and sometimes the femora) are red. The markings on both the scutum and abdomen of the male are also red. On females, the antennae; the markings on the face, thorax and abdomen; and the legs below the trochanters, are deep red to orange-red. The first segment of the abdomen usually has a continuous (not broken) band. This species runs 7-8 mm.
CITE THIS PAGE: Sharp, Paula and Ross Eatman. "Anthidiellum." Wild Bees of the National Butterfly Center of Mission, Texas. 15 Jan. 2019, http://www.wildbeestexas.com. Accessed [day/month/year guide accessed].