NORTHERN CACTUS WOOD-BORER BEE
In March 1917, Wilmatte Porter Cockerell, one of America’s first women entomologists, took a road trip along the Texas border. She described the journey as an excursion through the Texas bush, in which she was grateful to rely on the skillful driving of her companion Miss Mary Cowgill. Along the way, Cockerell stopped to document bees and other insects. She recorded her findings in a travelogue titled Collecting Bees in Southern Texas.
Cockerell discovered several new species, among them the singular Eucera Wilmattae long-horned bee. One of her discoveries was the cactus wood-borer Lithurgopsis littoralis shown here: she stumbled on an unusual male bee in Port Isabel, located in the Lower Rio Grande Valley about 80 miles from where the National Butterfly Center now lies.
Wilmatte Cockerell’s journal begins with a rapt description of prickly pear cactus and the many-colored prickly poppies that filled the landscape along the Lower Rio Grande Valley in March 1917. More than 100 years later, these plants still adorn spring landscapes in southmost Texas. In March and April of 2019 at the National Butterfly Center, the littoral cactus wood-borer bee stationed itself almost exclusively on prickly poppies and prickly pear.
In late March 2019, male Lithurgopsis littoralis bees began appearing in conspicuous numbers on pink prickly poppies (Argemone sanguinea) and golden prickly poppies (Argemone aenae) at various sites of the Lower Rio Grande Valley proximate to Mission, Texas.
According to Texas bee expert Jack Neff, President of the Central Texas Melittological Institute, prickly poppies furnish abundant pollen, but very little nectar. Because male bees drink nectar but do not gather pollen, cactus wood borers in all likelihood gather in these flowers because they are comfortable shelters from wind and rain where the male bees can await the bloom period of Texas prickly pear cactus and the emergence of female bees from their winter nests.
Once Texas prickly pear cactus began to bloom (about two weeks after the prickly poppies), male Lithurgopsis were found nearly exclusively in prickly pear cactus flowers.
In early April 2019, female cactus wood-borer bees were first seen emerging from their holes and visiting the flowers of Texas prickly pear. The female bees would dig deeply into the anthers of the cactus flowers, often disappearing in their depths, despite the bees’ large size. The blossoms of Texas prickly pear produce exuberant amounts of pollen. Upon emerging from the blossoms, female bees often appeared covered with the pollen, as if they had been rolled in corn flour.
Physical Characteristics of Lithurgopsis bees
Wood-borer bees are close cousins of leafcutter and resin bees. The wood-borer genus Lithurgopsis belongs to the same family (Megachilidae) as leafcutters, but to a different subfamily – Lithurginae. Within the United States, this subfamily is represented principally by bees associated with cactus, known collectively as Northern cactus wood-borer bees.
Lithurgopsis littoralis bees look a little like hefty leafcutter bees. Both male and female cactus wood-borer bees have sculpted dark heads; abdomens that taper abruptly at the end; and pale bands of hairs striping their abdomens, all traits of many leafcutters. Female Lithurgopsis littoralis bees carry pollen on long pollen-collecting scopal hairs located on their abdomens, much like their female leafcutter counterparts.
Nonetheless, even to the naked eye, Lithurgopsis littoralis bees are distinctive – both males and females have opaque black eyes, robust builds and and large heads; females have horn-like projections on their faces.
Viewed under a macro lens, other notable traits emerge: the male Lithurgopsis litoralis has spikelike protrusions on its clypeus (the face-part above the jaws). Female Lithurgopsis litoralis bees have a pronounced bulbous ridge at the top of the clypeus.. The tibia (leg segment just below the knee) of the hind leg of a Lithorgopsis is covered with small bumps. These traits are shown in the photo strips below.
According to Texas bee expert Jack Neff, Lithurgopsis bees within a species can be quite variable in size. This results at least in part from that fact that Lithurgopsis have odd nests without well- defined cells; egg chamber size varies, and thus so does the size of hatchlings.
Lithurgopsis range and behavior
Wood-borer bees are seldom featured in popular North American native bee guides and databases. Within the United States, they are represented by a mere 6 species (Lithurgopsis apicalis, L. echinocacti, L. gibbosa, L. listrota, L. littoralis and L. planifrona). They are found mostly in arid habitats of western states and along the US. Mexican border and, and tend to prefer feeding on plants of the cactus family.
The species Lithurgopis littoralis occurs principally in south Texas and Mexico but has been documented as far north as Oklahoma, Kansas and even Illinois. Its name (littoralis means "coastal") reflects the fact that Wilmatte Cockerell found her specimen of the bee in Port Isabel, located by the Gulf of Mexico.
There is little widely available research on Northern cactus wood-borers. In 2014, the renowned entomologists Jerome G. Rozen and Glenn Hall published a study on the nesting behavior of Lithurgopsis apicalis, a Northern cactus wood-borer of the western United States. Rozen observed this bee in Arizona building nests nests by chewing out tunnels in dead and dying flower stalks of Agave cactus.
An exotic species of wood-boring bee raised alarms in the 1970’s when it arrived in Pennsylvania and New Jersey. Called Lithurge chrysurus, the bee was a native of Mediterranean Europe and said to be able to bore through new wood structures that required humans axes, chisels, and hammers to penetrate, including compressed wood-fiber shingles and even vinyl. This wood-borer bee's potential for doing great damage to buildings and bridges spurred a flurry of studies but ultimately the bee, a specialist on knapweed flowers, proved easy to contain. Its American counterparts seem content with cactus.
Littoral Cactus Wood-borer Bee
Size: 9-14 mm (male); 14-15 mm (female)
Associated plants at NBC:
Golden prickly poppy
Plant Family: Papaveraceae
Red prickly poppy
Plant Family: Papaveraceae
Texas Prickly Pear
Plant Family: Cactaceae
TAXONOMY OF LITHURGOPSIS
Species found at National Butterfly Center:
(Littoral cactus wood-borer bee)
A golden prickly poppy (Argemone aenea)
A male Lithurgopsis littoralis cactus wood-borer bee
A female Lithurgopsis littoralis on a prickly poppy (Argemone sanguinea)
A Lithurgopsis littoralis female on a prickly pear blossom
A Texas prickly pear cactus blossom (Opuntia engelmannii)
A female Lithurgopsis littoralis on a prickly pear blossom
A female Lithurgopsis littoralis from above: note the bee's robust build.
A female bee on prickly pear
Head of a female Lithurgopsis littoralis: two curved hornlike protuberances project from the front of the female bee's face.
The Female Lithurgopsis has a prominence or thick ridge on the "forehead" just under the antennae. On this species, Lithurgopsis littoralis, the prominence is very broad. This trait helps distinguish L. littoralis from the similar L. gibbosa, another cactus wood-borer bee species sometimes found in the Lower Rio Grande Valley.
Profile of a female Lithurgopsis littoralis, showing hornlike projections
A male Lithurgopsis littoralis
This is a large bee, with a very long body and long hind legs.
The powerful hind legs of the male bee
The bee foraging for nectar in a prickly pear flower & spreading its long back legs for leverage against the petals.
This male bee has a pitted face and somewhat protuberant clypeus. Note the spikes on the male bee's legs.
Face of male bee: On male Lithurgopsis littoralis bees, the supraclypeal area (under the antennae) is shiny and sparsely pitted. According to bee expert Jack Neff, this trait helps distinguish this species from the similar Lithurgopsis gibbosa, in which the same area is dull and densely pitted.