Genus Melitoma - Tribe Emphorini
The antics of Melitoma marginella
In November 2018, if you walked through the National Butterfly Center and peered into the deep throats of yellow esperanza flowers, you would see dozens of Melitoma marginella peering back at you with their rust-orange faces. Within a few seconds of your approach, the bees would reel off to fly back and forth amid the trumpet-shaped blossoms, occasionally stopping to drink nectar from the flowers.
As the days reached evening, male Melitoma ensconced themselves inside the esperanza blossoms. In the morning, you could gaze into almost any esperanza flower and find the bees there. When a cold rain set in, the bees crawled deeply into the flowers, tucking their abdomens into the blossoms' depths. The wide mouths of the downturned blossoms served as umbrellas, keeping the bees dry during the rain.
In mid-November, temperatures in the customarily hot Lower Rio Grande Valley plummeted into the thirties and forties. The cold snap caused esperanza bushes to wilt, and gusty winds pulled their half-spent blossoms from the branches. Female bees crawled into their underground nests, while male Melitoma clung to their holds inside the flower-throats of esperanza, floating through the air as the blossoms parachuted to the ground like escape pods. If you walked across the grounds picking up the esperanza flowers, you would find the Melitoma males still intact inside, clinging to their flowers, once again staring up at you with their orange faces.
When cold rains recommenced, the male Melitoma remained housed inside the cast-off flowers, still relatively dry and drinking what remained of the esperanza nectar. As the cold snap gave way to warmer weather, the male bees drifted back to newly-opening esperanza blossoms and continued visiting them until November gave way to winter.
Traits of chimney bees and ranges of Melitoma
Melitoma belong to the chimney bee tribe Emphorini, within the subfamily Eucerinae. Chimney bees are found only in the Western Hemisphere. Within the Lower Rio Grande Valley, Emphorini divide into two genera: Melitoma and Diadasia. A third chimney bee genus, Ptilothrix (hibiscus bees), is also found in Texas, north of the Valley.
Chimney bees are typically hairy and robustly built. Male chimney bees have long legs. Males also tend to have short antennae, a trait that sets them apart from males of similar tribes, such as longhorn bees (Eucerini). Melitoma are distinguished in part from other chimney bees by two features: (1) Melitoma have a particularly long proboscis (tongue-like mouthpart); and (2) distinctive patterns of light and dark hairs on the thorax.
Only three species of the genus Melitoma exist north of the Mexican border: Melitoma marginella; Melitoma taurea (shown below), which is found principally in the eastern United States and appeared only recently in Starr County; and Marginella grisella, whose populations stretch in a wide band from New Mexico, upward through the middle third of the country, to North Dakota.
Esperanza and Floral Preferences of Melitoma
All three Melitoma species found in the United States are considered specialist pollinators of flowers of the morning glory family, Convolvulaceae, particularly those in the genus Ipomoea.
Melitoma marginella is commonly associated with the red-center morning glory (Ipomoea amnicola) and the pink morning glory (Ipomoea carnea). Melitoma grisella, known oddly enough as the mallow bee, favors the purplish-pink bush morning glory (Ipomoea leptophylla). Melitoma taurea is associated with the big-root morning glory (Ipomoea pandurata).
Specialist bees do not always restrict their feeding habits to their proclaimed specialist plants, however. This is particularly true of male bees, which drink nectar from blossoms but do not gather pollen. At the National Butterfly Center, both male and female Melitoma marginella show a strong preference for esperanza, despite the fact that two morning-glory-family species grow there (Merremia dissecta and Ipomoea amnicola).
The Melitoma taurea female featured at the bottom of this page was also found visiting esperanza. It is notable that crooked-legged bees (Ancyloscelis), shown later in this guide, are also morning glory specialists that nonetheless visit esperanza. Perhaps the trumpet shape of esperanza flowers is inviting to bees accustomed to the similarly-shaped blossoms of morning glories.
Esperanza (Tecoma stans) is a neotropical plant with showy clusters of yellow flowers. It is native to the Mexican state of Tamaulipas, directly to the south of Hidalgo Co., Texas. Well-adapted to endure the vagaries of unpredictable November temperatures in southern Texas, esperanza is a reliable and sustained nectar source during cold Lower Rio Grande Valley autumn days.
Female Melitoma and their nesting behavior
All three Melitoma species of the United States are solitary ground-nesting bees that sometimes build nests in close proximity to one another, forming small aggregations. Melitoma often build long, tubular constructions made of dried mud at their tunnel entrances, which resemble turrets or “chimneys” – this practice gives the genus its common name of “chimney bee”. Female bees carry water from nearby areas, using it to moisten the soil near their tunnel entrances. They then reshape the moistened soil into pellets utilized to construct their turrets.
Melitoma marginella seek out dry river banks, clayey soils or adobe structures that are relatively near water sources and stands of morning-glory family plants. At the National Butterfly Center, Melitoma marginella are most common in sites that line an irrigation canal paralleling the Rio Grande River, where alamo vine and esperanza grow close by. Female Melitoma marginella emerge at the National Butterfly Center in mid-April to begin gathering nectar and pollen from these flowers.
Mexican, Central American and South American Melitoma have been observed taking advantage of pre-existing structures in order to evade nest construction themselves. Studies have documented Melitoma taking over abandoned termite nests and and settling into porous brick walls; the eaves of wattle-and-daub houses; the overhangs of mine entrances; and outdoor clay ovens. Melitoma also have been discovered occupying abandoned nests originally constructed by crooked-legged bees, whose life cycles and floral preferences tend to jibe with those of Melitoma.
A male Melitoma marginella chimney bee
Female and male Melitoma marginella meeting on a leaf
Esperanza, a favored plant of Melitoma at the NBC
The reddish and elongated hind legs of a male Melitoma marginella
TAXONOMY OF MELITOMA BEES
Species shown below:
Melitoma Species of the National Butterfly Center & Lower Rio Grande Valley
Marginate Chimney Bee
Size: 8-10 (male and female)
Plant Family: Convolvulaceae
Plant Family: Bignoniaceae
(male bees only; rarely)
Plant familly: Passifloraceae
When seen: April 2019,
November 2018 & 2022,
A male Melitoma marginella: Note the slight yellow tinge to the pale stripes on the bee's abdomen: this is a subtle feature of some individual specimens of this species found at NBC. Cresson wrote that this trait helped distinguish M. marginella from the similar M. taura, whose pale abdominal bands are always white.
Note also the bee's long proboscis (a tubular, tongue-like mouthpart), a distinctive trait of the genus Melitoma.
Melitoma marginella have bright orange faces. This is a male Melitoma marginella ensconced inside an esperanza blossom during a rainstorm: the bee has pushed himself deep into the flower to avoid getting wet.
A female melitoma marginella: note the bee's robust build, a trait of chimney bees generally (particularly females).
Like their male counterparts, female Melitoma marginella have rust-orange hair on their faces.
Close-up of face of a female Melitoma marginella
A male Melitoma marginella
A female Melitoma marginella
Melitoma marginella are medium-sized bees with bright rust-orange hairs on their faces; thoraxes covered with black, gray and white hairs; and black abdomens banded with pale hairs. As noted further below, the bands on the bees' abdomens may have a yellowish cast. The bees' legs are mostly black, with red lower tarsi and partly-red hind basitarsi and femurs. Females’ legs are shorter than males’ and fringed with long, black hairs. Females’ hind-leg scopal hairs are long and feathery. Both males and females have black eyes and black antennae.
Melitoma marginella is the dominant Melitoma species of the Lower Rio Grande Valley. It is considered a neotropical species and is recorded as far south as Ecuador. Within the United States, Melitoma marginella is relatively uncommon and occurs principally along the southern Texas border.
A female Melitoma taurea
Bull Chimney Bee
Size: Females 10-12.5 mm
Males 9.5 - 12 mm
Plant Family: Bignoniaceae
When and where seen:
June 12, 2021
Falcon State Park
Roma, TX (Starr County)
Range Extension for Species
A female bull chimney bee (Marginella taurea): note the bold white bands on the bee's abdomen and the dense black, feathery scopal hairs on its hind legs.
The female bee has a a robust build. This female measures 11 mm.
Face of the female Melitoma taurea: the bee's clypeus is black, and it lacks the bright orange facial hair characteristic of Melitoma marginella. The hairs on this female's vertex are light-and-dark intermixed.
Dorsal view of bee: the thorax hairs are black, white and pale orange.
Range Extension for Melitoma taurea
The female Melitoma taurea shown here appeared at Falcon State Park of Starr County in June, 2021. The bee's appearance marks a range extension for this species. As noted above, the Melitoma taurea was found feeding on esperanza, like its Melitoma marginella counterpart at the National Butterfly Center 50 miles away -- although both species are considered specialists of morning-glory family flowers (Convolvulaceae).
Melitoma taurea vs. Melitoma marginella
In 1872, American entomologist Ezra Townsend Cresson completed Hymenoptera Texana, in which he catalogued more than 600 insects collected in Bashtrop, Bosque, Dallas and Travis Counties of Texas. This work contained the first published description of the species Melitoma marginella (under the name Melissodes marginella).
Cresson noted that Melitoma marginella closely resembled Melitoma taurea. He wrote, however, that Melitoma marginella can be distinguished from M. taurea fairly easily by the color of the bees' facial hair: that of Melitoma marginella is rust-orange, while that of M. taurea is dark gray. In addition, Cresson noted that the pale bands on the abdomens of Melitoma marginella' sometimes have a yellowish tint, a trait lacking in Melitoma taurea.
These two species differ in other respects as well: Melitoma taurea is more robustly-built, and its legs are also entirely black, while Melitoma marginella has dark-red coloring on its hind legs. Melitoma marginella also has a U-shaped pattern formed by dark hairs on its thorax, while the hair pattern of thorax hairs on M. taurea is more haphazard. Finally, within the United States, Melitoma marginella is found primarily in southern Texas, while M. taurea is more widespread.
CITE THIS PAGE: Sharp, Paula and Ross Eatman. "Melitoma." Wild Bees of the National Butterfly Center of Mission, Texas. 15 Jan. 2019, http://www.wildbeestexas.com. Accessed [day/month/year guide accessed].