MELITOMA MARGINELLA CHIMNEY BEE
The antics of Melitoma marginella bees
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 orange-faced Melitoma marginella bees peering back at you. 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 bees ensconced themselves inside the esperanza blossoms. In the morning, you could peer 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 completely dry during the rain.
In mid-November, temperatures in the generally hot Lower Rio Grande Valley plummeted into the thirties and forties. The cold snap caused esperanza bushes to wilt and drop their yellow blossoms. Female bees crawled into their underground nests, while male Melitoma clung to their holds inside the flower-throats, drifting through the air as the esperanza blossoms parachuted to the ground like escape pods. If you then 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 Melitoma bees 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.
Where Melitoma marginella bees are found
Within the United States, Melitoma marginella is found only in southern Texas. It is considered a neotropical species, and is recorded as far south as Ecuador. (Neotropical means "of New World tropical and subtropical areas".)
Only two other species of the genus Melitoma exist north of the Mexican border: Melitoma taurea, which is found principally in the eastern United States; and Marginella grisella, whose populations stretch in a wide band from New Mexico, upward through the middle third of the country, to North Dakota.
Specialist flowers and Melitoma marginella's preference for esperanza blossoms at the National Butterfly Center
All three United States Melitoma species are considered specialist pollinators of morning-glory-like plants of the 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 considered a specialist pollinator of 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, male Melitoma marginella bees show a strong preference for esperanza over the two common species of morning-glory-tribe plants that grow there (the magenta-throated white flower known as alamo vine, and the pink morning glory). Females frequent both alamo vine and esperanza.
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, for bees accustomed to spending their lives in deep-throated flowers.
It is notable that both female and male crooked-legged bees, which are also presumed specialists of morning glories and their close kin, are similarly attracted to esperanza at NBC. Aztec sweat bees, generally associated with alamo vine, also appear in significant numbers on NBC esperanza bushes in late November.
Female Melitoma bees and their nesting behavior
Female Melitoma marginella bees emerge at the National Butterfly Center in mid-April to begin gathering nectar and pollen for their nests. The bees construct their nests by digging long tunnels in which they form brood cells. After mating, female Melitoma marginella lay eggs in the brood cells, which the bees provision with pollen stores for their offspring to feed on when they hatch.
All three Melitoma species of the United States are solitary bees that sometimes build nests in close proximity to one another, forming small aggregations. Melitoma bees 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 bees 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 bees are most common in areas that line an irrigation canal that parallels the Rio Grande River, where alamo vine and esperanza are both close by.
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. One Melitoma species was observed occupying nests that had been constructed by crooked-legged bees, whose life cycles and floral preferences tend to coincide with those of Melitoma.
CITE THIS PAGE: Sharp, Paula and Ross Eatman. "Melitoma Chimney Bees." Wild Bees of the National Butterfly Center of Mission, Texas. 15 Jan. 2019, http://www.sharpeatmanguides.com. Accessed [day/month/year guide accessed].
A male Melitoma marginella chimney bee
A male Melitoma marginella chimney bee peering from an esperanza blossom that fell to the ground after a cold snap
The back legs of male Melitoma marginella chimney bees are distinctly reddish.
Esperanza, a preferred plant of male Melitoma bees at the NBC
Esperanza, a preferred plant of male Melitoma bees at the NBC
TAXONOMY OF MELITOMA BEES
Species shown below:
Melitoma Chimney Bee Species of the National Butterfly Center
Melitoma marginella Chimney Bee
Size: 8-10 (male and female)
Food plant at NBC:
Plant Family: Convolvulaceae
Plant Family: Bignoniaceae
(male bees only; rarely)
Plant familly: Passifloraceae
November 2018, April 2019
A female Melitoma marginella
Species identification of Melitoma bees:
Melitoma marginella, Melitoma taurea and Melitoma grisella.
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 another melitoma species known as 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.
These two species differ in other respects as well: Melitoma marginella has dark red coloring on its hind legs; the pale hair bands on its abdomen sometimes have a slight yellowish tint; and, within the United States, M. marginella is found only in southern Texas, while M. taurea is more widespread.
M. marginella and M. taurea are otherwise remarkably similar. Both species are medium-small (between 9 to 12 millimeters or 1/3 to 1/2 inch), with females larger than males. Both species have dark abdomens banded with well-defined pale stripes. The two species also have similar symmetrical patterns of dark-and-light hairs on the head and thorax. On both, a loosely-defined u shape of dark thorax hairs angles downward over the bee's sides (as shown in the photo strip at left). Dark hairs line the back portion of the thorax on both species as well. Males of both M. marginella and M. taura have elongated hind legs.
There are only three species of bees in the genus Melitoma found within the United States: The last of these, Melitoma grisella chimney bees, are quite distinct from the other two. M. grisella is a fuzzy-looking pale bee with a striped abdomen. The head and thorax hairs of M. grisella are entirely off-white or a very pale yellow.