CROOKED-LEGGED BEES

Genus  Ancyloscelis

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Male Ancyloscelis bees are easily recognized by their elongated and ornately curved hind legs.  The genus name “Ancyloscelis,” which means “crooked-leg,” derives from this singular feature.

Male Ancyloscelis bees use their long, hooked legs for leverage when mating or feeding.  They spread their back legs to keep from falling into wide-mouthed flowers as they sip nectar, or as they peer down into blossoms in search of mates. 

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At the National Butterfly Center, female crooked-legged bees are usually found gathering pollen from the pink-and-white flowers of alamo vine, their heads plunged into its deep-throated  blossom, with only their striped abdomens visible from above.  Males fly in quick figure-eight patterns as they patrol vegetation frequented by females. At night, Ancyloscelis males sleep hanging by their jaws from plants visited by females during the day.

According to Michener, McGinley & Danforth’s The Bee Genera of North and South America, crooked-legged bees  are rare within the United States.  Ancyloscelis is a neotropical genus, occurring principally in Mexico, Central and South America.  Although approximately 20 species live south of the Texas border, only three inhabit the United States:  Ancyloscelis apiformis; A. melanostoma; and A. sejunctus.  These appear nearly exclusively in Texas and a handful of southwestern states.

 

Crooked-legged bees at the NBC belong to the species Ancyloscelis apiformis.  They are most numerous  in  NBC areas abutting canals running from the Rio Grande.  Ancyloscelis apiformis bees tend to nest in shaded, vertical banks like those along the canal's edge.  These bees are solitary, each provisioning its own nest.  Nonetheless, they often build nests in close proximity to one another, and can form large aggregations.
 

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Plant preferences: 

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All three Ancyloscelis species found in the United States specialize in flowers of the Convolvulaceae family and are particularly drawn toward members of the morning glory genus Ipomoea. Thus, one productive method for finding these bees is to seek out morning-glory-like flowers and to observe what insects visit them. 

 

As noted, Ancyloscelis apiformis is closely associated at NBC with alamo vine (Merremia dissecta).  This blossoming vine is a member of  the same plant family as morning glories -- Convolvulaceae.  Alamo vine flowers are large and trumpet shaped; they look like white morning glories with magenta centers (shown below right).

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Ancyloscelis species’ strong preference for Convolvulaceae plants has led to an often-repeated generalization that North American crooked-legged bees feed exclusively on flowers of this family – this is not strictly true, however.  At the National Butterfly Center, both male and female crooked-legged bees are frequently seen on esperanza (Tecoma stans), a ubiquitous native ornamental shrub in the plant family Bignoniaceae. 

 

The proclivity of Ancyloscelis bees for visiting esperanza has been well-documented among Ancyloscelis bee populations in Central America. Thus, another method for locating these bees might be to peer into the yellow trumpet-shaped blossoms of esperanza.

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Identification information:

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Female and male Ancyloscelis apiformis bees differ in appearance:  males are slighter smaller (6 mm) than females (8 mm) and more readily identifiable because they possess long, hooked legs.

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The hind legs of female Ancyloscelis are not hooked and elongated like those of males. Instead, females have more conventionally-shaped hind legs.  Their scopal (pollen-collecting) hairs are stiff, widely-spaced and feathery-looking, a characteristic common to members of the bee tribe Emporini.  Male crooked-legged bees are rarely far from their female counterparts, however -- and thus the easiest way to identify a female Anycyloscelis is to wait to see whether a crooked-leg male arrives to pester her.

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In other ways, males and female Ancyloscelis apiformis bees are generally alike:  they are small, fairly hairy bees with short, robust bodies and black abdomens striped with crisp white bands.  Their faces are oval, and their heads relatively small (narrower than their thoraxes.) 

 

Female and male Ancyloscelis apiformis  bees have similar antennae, and both may have pale markings on their mandibles.  Males additionally may show extensive pale patterns on their clypeuses and labrums (the face parts above and between the jaws).  Both male and female bees’ clypeuses are sometimes markedly protuberant, giving them a roman-nosed look in profile.

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All of these traits are illustrated in detail in the photo strips below.