#11

THE FLOWERS BUTTERFLIES AVOID:
The Mysterious World of Bees, Prickly
Poppies and Texas Prickly Pear Cactus

In March 1917, Wilmatte Porter Cockerell, one of America’s first women entomologists, took a road trip through the Lower Rio Grande Valley, along the Texas-Mexican border. She described the journey as an excursion through the Texas bush, made possible by the skillful driving of her companion Miss Mary Cowgill. 

Along the way, Cockerell stopped to document bees and other insects.  The Lower Rio Grande Valley is known for its singular habitats and biodiversity, and Cockerell discovered several unique and previously undocumented bee species – among them the Parkinsonia carpenter bee, the littoral cactus woodborer bee and Willmatte’s Tetraloniella.  She recorded her findings in a travelogue titled Collecting Bees in Southern Texas.

Wilmatte Cockerell’s journal begins with a rapt description of the many-colored prickly poppies and prickly pear cactus blossoms that ornamented the Lower Rio Grande Valley in March 1917.  More than 100 years later, these plants still adorn spring landscapes in the valley's Hidalgo County, where the National Butterfly Center is located. And the bees that enchanted Wilmatte Cockerell more than one hundred years ago are still visiting the same prickly poppy and prickly pear flowers at the NBC.  [Fig. 1]

Every time I encounter a bee  that was first described generations ago, I feel a renewed sense of astonishment:  I  harbor an unexamined worldview that my kind, Homo sapiens, has trampled my country for so long that few of its natural enchantments remain:  there are no virgin forests in most of America, no oceans of buffalo flooding endless prairies.  I live in a modern world of hydrangeas and pigeons. 

Thus, when I stumbled on Wilmatte’s Tetraloniella at the National Butterfly Center during fall 2018, I felt as if I had found a unicorn.  And I felt pinioned by my awareness that a century ago, Wilmatte Cockerell had seen the same face staring back at her from a Texas flower:  a charming creature, with a yellow mask and absurdly long antennae that curled at the tips like the ends of a mustache.  This species, found only in Texas and Northeastern Mexico, is one of many native bees described by Cockerell that I would encounter that fall at the National Butterfly Center. [Fig. 2]

THE USES OF PRICKLY POPPIES 

Wilmatte Cockerell’s Collecting Bees in Southern Texas steered me to explore the remarkable network of interactions among bees, prickly poppies  and Texas prickly pear cactus, a micro-ecosystem that has stood the test of time.  [Fig. 3]

Texas Prickly pear and prickly poppy are stellar examples of the fact that plants largely ignored by butterflies are often bee magnets.  This phenomenon reflects the differing survival requirements of these two pollinator groups.  Both male and female bees drink nectar, and thus they are attracted to many of the same flowers visited by butterflies. Female bees, however, target some flowers principally for their pollen, which the bees store in their nests for their offspring to eat after hatching.

 

Female bees also visit plants to collect resins, oils and other materials for building nests.  An example is the silver-tailed petalcutter (Megachile montivaga), which trims and transports flower petals to line its egg chambers.  Usually associated with flowers that have large and delicate petals such as evening primrose and clarkia, this bee uses Argemone prickly poppies for nesting materials in the Lower Rio Grande Valley. [Fig 4]

  

Butterflies pay little attention to prickly poppies of the genus Argemone.  Many Texans neglect the flowers as well, viewing them as annoying weeds:  along the Lower Rio Grande border, prickly poppies ornament vacant lots, the edges of railroad tracks and untended fields.  To an outsider seeing them for the first time, however, Argemone poppies are eye-catching:  often three to four feet tall, they have multiple stems bearing chalice-shaped yellow, pink or white tulip-sized blossoms.  The delicate flowers are adorned at the center with a mesmerizing tangle of gold-tipped reddish stamens.  Intricately wrought spines arm the leaves and pods.  

Prickly poppies, which begin flowering in March, just before prickly pear cactus blooms in the Lower Rio Grande Valley, are also an essential part of the world of cactus-pollinating bees. 

 

The littoral cactus woodborer named by Wilmatte Cockerell provides a good example of the interplay between the pollination of prickly pear and Argemone poppies.  This species is a promient cactus pollinator.  Lithurgopsis littoralis has a wrestler's build, hefty jaws and unusually long legs -- features that allow it to tunnel into cactus and to navigate the quicksand of dense, viscous stamens at the center of prickly pear blossoms. [Figs. 5 & 6]

Nonetheless, male littoral cactus woodborer bees emerge weeks before the first prickly pear cactus blooms in the region and ensconse themselves in prickly poppies.  At the National Butterfly Center, if you peel back the petals of prickly poppies in early spring, chances are you will find a male Lithurgopsis littoralis peering back up at you. 

I was puzzled by this when I first began photographing Lithurgopsis littoralis in March 2019, as part of a project to document native bees at the National Butterfly Center. I never saw male cactus woodborer bees feeding on poppies:  they simply appeared to frolic in the flowers by day and to sleep in them by night.  I observed this behavior in another species associated with prickly pear as well:  male Diadasia rinconis chimney bees, commonly known as "cactus bees," began appearing in the prickly poppies, alongside the cactus woodborers.  Diadasia rinconis was one of the species Wilmatte Cockerell had identified on her 1917 trek through the Lower Rio Grande Valley bush. [Fig. 7]

I consulted Jack Neff, President of the Central Texas Melittological Institute, who has been a lifeline throughout our NBC bee-documenting project.  Equipped with an encyclopedic knowledge of Texas bees acquired through a lifetime of entomological observation, Neff has made himself continuously available for bee identifications, pointing us toward written resources and supplying us with a stream of anecdotal information about the floral preferences and behavior of unusual Texas species.

According to Jack Neff, prickly poppies furnish abundant pollen, but admittedly little nectar.  Because male bees drink nectar but do not gather pollen, male cactus woodborers and cactus Diadasia in all likelihood gather in these flowers because they are comfortable:  the cup-shaped blossoms shelter them from wind and rain while the male bees await the emergence of females from their winter nests.

The usefulness of flowers as outdoor shelters plays a large role in the lives of many male native bees.  Most female bees spend their days building nests underground or in plants, laying eggs and stocking their nests with pollen; afterward, the females often pass the night in their own nests.  Male bees, by contrast, tend to live and sleep outside, braving the elements.

I had seen male bees before at the NBC engaging in shelter-oriented behavior, allying themselves with specific plants because of their durability in tempestuous weather.  During the fall of 2018, male bees of one Lower Rio Grande Valley species, Melitoma marginella, camped out during rainstorms in the trumpet-shaped flowers of the ornamental bush esperanza:  when the blossoms were blown off of trees, the male bees clung to their insides, riding the flowers like escape pods as they parachuted to the ground.  The male bees then hunkered down inside the flowers' deep throats, keeping dry until the rain subsided.  [Fig. 8]

THE LITTLE PRICKLY PEAR LONG-HORNED BEE
AND T. D. A. COCKERELL

In late March 2019, after male cactus woodborer bees and Diadasia rinconis cactus bees were well-established in prickly poppies, males of two other species began to appear on the flowers.  The first of these was the compact Anthophorula (Anthophorula compactula), a small, handsome bee endemic to Mexico, Texas and the American southwest. This bee emerges in Hidalgo County only during the spring months when poppies and prickly pear cactus are in bloom.  [Fig. 9]. 

 

The advent of this Anthophorula was accompanied by the appearance of male long-horned bees of a beautiful species we had never seen before, either in nature or in Internet databases.  The bees were barely 1/3 inch (9 mm) in length, with bright blue eyes, bold bands of white hair striping their abdomens and reddish legs  [Fig 10].  Like male littoral cactus woodborer bees and Diadasia rinconis, males of these two newly-arrived species slept in the poppies and sought shelter in them during inclement weather, but were never observed feeding on the flowers.

This quartet of bees appeared so consistently on the prickly poppies that my fellow photographer Ross Eatman and I began to call them the Fab Four.  The same species would later prove to dominate any grove of prickly pear cactus we encountered in Hidalgo County.  We had difficulty, however, tracking down information on the fourth member of the quartet. 

Bees are generally harder to identify than butterflies.  Differences among bee species are often nuanced and invisible to the naked eye:  leafcutter bees, for example, are distinguished by the number of teeth on their jaws, while long-horned bee males are identified in part by the comparative lengths of the 13 segments of their antennae. 
 

Bees of the Lower Rio Grande Valley offer particular challenges, because they are often unique to the area and understudied.  We frequently found ourselves combing through taxonomic records from the late 1800's and early 1900's, in order to identify bees we encountered at the National Butterfly Center.

A century ago, taxonomic descriptions were the verbal photography of the pre-digital age -- records written in an obsessively-precise language accessible to entomologists everywhere but impenetrable to almost everyone else.  (For example, the record most closely fitting our small long-horned bee read in part:  "Flagellum very broadly bright orange-fulvous beneath, reaching onto the  middle of the scutellum; mesothorax and scutellum shining … nervures dusky ferruginous…”) .

We sent a dozen photographs of our long-horned bee, taken from every conceivable angle, to Jack Neff.  Within a few days, he pointed us to Melissodes opuntiellus (literally “the little prickly pear long-horned bee").  The single written description we could find of this species was dated 1911 and perfectly matched our bee.  As it turned out, Melissodes opuntiellus had been first recorded that year by none other than Theodore Dru Allison Cockerell – the husband of Wilmatte Cockerell.   

Described by biographer Arnold Mallis as sporting “a long flowing beard like some ancient prophet’s,” T. D. A. Cockerell was a giant of the entomology world in his day, the author of more than 3000 articles, who documented over 9000 varieties of insects. Although he never acquired an advanced degree in science, Cockerell taught Zoology at the University of Colorado in Boulder for thirty years.

Born in 1866 in a London suburb, Cockerell described himself as a sickly child, sent frequently to the countryside by adult relatives who doubted he would survive to adulthood. Cockerell later attributed his love of nature and his passion for insects to the fact that he had spent much of his boyhood wandering in fields and woodlands.

Cockerell developed tuberculosis before the age of twenty.  He relocated to the United States in search of a climate that would restore his health, settling eventually in Colorado.  There, he defeated his tuberculosis and began recording American bee species.  In 1891, Cockerell married his first wife, Annie Fenn, and moved with her to Jamaica to commence employment as curator of the Kingston Public Museum. 

The couple's life together was marked by a succession of tragedies. Their first son died in infancy, and the humid Jamaica climate rekindled Cockerell's tuberculosis.  He and Annie relocated to New Mexico, where she died in childbirth in 1893.  The couple's second son died in early childhood of diphtheria. 

 

Cockerell engrossed himself in the study of bees.  In 1899, during a bee-collecting expedition in New Mexico, he met Wilmatte Porter, who was then a recent Stanford graduate teaching biology at a local normal school.  In 1900, she and T. D. A. Cockerell married. By all accounts, this event heralded an upward turn in what would become a happy and adventurous life, rich in entomological discoveries. 

 

In 1903, the Cockerells set up house in Colorado. Over their 48-year marriage, Wilmatte and T. D. A. engaged in a partnership of scientific study, establishing an agricultural experiment station together, co-authoring several articles and travelling throughout the world on insect-collecting and botanical expeditions to places as far-flung as India, Siberia, Morocco and the Lower Rio Grande Valley.

In 1911, Cockerell submitted an article titled “Some New Bees from Flowers of Cactaceae" to The Canadian Entomologist, in which he recorded Melissodes opuntiellus.  Cockerell’s observations of the species were based on three Texas specimens found between 1905 and 1908 feeding on prickly pear.  The last, a male, had been discovered in Brownsville, the largest of the  southernmost towns of the Lower Rio Grande Valley.  [Fig. 11]

After confirming the identification of our Melissodes opuntiellus, we would learn that T. D. A. Cockerell had also been the first to describe the cactus bee Diadasia rinconis, and the compact Anthophorula, both in 1897.  Between the two of them, Wilmatte and T. D. A. Cockerell had uncovered all members of the Fab Four.  [Fig.12]

THE TEXAS PRICKLY PEAR CACTUS BLOOM

About three weeks after the first prickly poppies opened in at the National Butterfly Center in 2019, Texas prickly pear cactus began blooming throughout Hidalgo County. The prickly pear bloom of the Lower Rio Grande Valley brings arid landscapes to life, like a traveling circus camping out for a month on the outskirts of a sleepy town.  [Fig. 13]

In early April, we took day trips through the Valley to examine prickly pear cacti between Hidalgo County and Point Isabel, which lies approximately 80 miles southwest of the National Butterfly Center.  In areas devoid of other flowers in early spring, the prickly pear cactus bloom attracted a parade of female bees.  

The flowers of Texas prickly pear (Opuntia engelmanni) are large and bowl-shaped, designed to accommodate many bees at once -- provided that the bees are equipped to negotiate the unique blossoms. The flowers have numerous, tightly packed stamens that form a gluey, deep center -- qualities likely to scare off butterflies -- but ones which provide a protective and rewarding environment for many native bee species. The stamens of prickly pear flowers are also thigmotropically sensitive, that is, the filaments move in response to contact, a phenomenon thought to enhance pollination.  

The blossoms of Texas prickly pear produce exuberant amounts of pollen.  In 1979, entomologists Verne Grant and Paul Hurd co-authored a study titled “Pollination of the Southwestern Opuntias,” in which they listed, in addition to various pollinator-beetles, a total of 41 species of native bees that pollinate prickly pear cactus in various habitats from California to Texas.

 

A universe of bees in the Lower Grande Valley benefits from the prickly pear bloom. During the April 2019 cactus bloom in Hidalgo County, we discovered a wide spectrum of generalist bees foraging for pollen on Texas prickly pear.  Among these were the dazzling emerald- green Aztec sweat bee (Augochlora azteca), a species endemic to the Texas-Mexican border; and the Tepanec long-horned bee (Melissodes tepaneca), a species Wilmatte Cockerell had documented on Lower Rio Grande Valley cactus during her 1917 trek.  [Fig. 14 & 15]

Also of note was the blue metallic mason bee Osmia subfasciata, which appeared in the first days of the cactus bloom. This small bee swarmed prickly pear plants throughout the county -- not for their pollen, but instead to harvest materials from the soft leaf buds that rim prickly pear pads in spring.  Mason bees derive their name from their practice of using masticated plant parts, mud and even pebbles to build nests.   We speculated that the mucilaginous leaves of the prickly pear provided an excellent base for mason bee nest mortar.   [Fig. 16]

By far, however, the most common pollinators of local Texas prickly pear were the Fab Four species we had discovered earlier on prickly poppy – the cactus woodborer bee Lithurgopsis littoralis; the cactus bee Diadasia rinconis; Anthophorula compactula; and the little prickly pear long-horned bee Melissodes opuntiellus.  The entire cactus bloom lasted for about six weeks, and during its entirety these four species remained a persistent and populous presence on prickly pear blossoms across the Rio Grande Valley.

 

In early April 2019 in throughout Hidalgo County, females of these four species emerged from their winter holes to mob Texas prickly pear flowers.  The female bees dug deeply into the anthers of the cactus flowers, disappearing into their depths. Upon emerging from the blossoms, the bees often appeared covered with the pollen, as if they had been rolled in corn flour. 

​After the female bees arrived, male cactus woodborer bees, little prickly pear long-horned bees and compact Anthophorula abandoned their roosts in Argemone poppies at the Butterfly Center and nearby preserves.  The male bees resituated themselves inside prickly pear cactus flowers, waylaying females as they busied themselves gathering pollen. 

 

Male ​Diadasia rinconis cactus bees continued to sleep in golden prickly poppies (Argemone aenea) from late evening through late morning all through April. One evening after a particularly violent thunderstorm during cactus-bloom season, we peered into dozens of golden prickly poppies at the National Butterfly Center, and found male Diadasia rinconis hunkered down in nearly every one. By day, the Diadasia males busied themselves busy patrolling cactus flowers. [Fig. 17]

 

​Also of note was the recurring interest of Fab Four female bees in prickly poppies. During the weeks when prickly-pear was blossoming, the cacti cycled through periods in which the bloom reached its full height and then seemed to end, only to be followed by a new phase of blossoming.  During the lulls, female wood -boring bees, Anthophorula compactula, Diadasia rinconis, and Melissodes opuntiellus would appear precipitously in large numbers on prickly poppies to harvest pollen.  

When the cacti recommenced blooming, these female bees returned to pollinating prickly pear.  The Argemone poppies, in addition to providing shelter for male bees, served as default pollen sources for females in landscapes where little else was in bloom.

Of these four species, only the Lithurgopsis littoralis woodborer bee might be deemed a cactus specialist.  As its name implies, the cactus woodborer bee makes use of cacti for purposes other than gathering pollen.  Female littoral cactus woodborers tunnel into the dead and dying flower stalks of cactus to build nests. The bees lay eggs in chambers at the ends of the tunnels, provisioning them with cactus pollen for their offspring.  Upon hatching, the larvae feed on the pollen, spin cocoons and pupate, all within the cactus plant.  [ Fig. 18]

 

​All of the other three species of the Fab Four nest in the ground and have been documented foraging on a variety of flowers.  During the Lower Rio Grande cactus bloom, however, we rarely observed any females of these species feeding on any other flowers other than prickly poppy and prickly pear.  After the bloom ended, the cactus woodborer bee and the compact Anthophorula vanished entirely.  Diadasia rinconis and little prickly pear long-horned bees lingered on, visiting a variety of available pollen sources until fading away near the end of June.

#1

Female Lithurgopsis littoralis cactus wood-brer bee - (c) Copyright 2019 Paula Sharp

A female littoral woodborer bee on a prickly poppy (Argemone sanguinea)

#2

WJPEG-Tetraloniella-1-Face-NBC-#51-Yello

A Wilmatte's Tetraloniella (Tetraloniella wilmattae), named after Wilmatte Cockerell 

#3

WJPEG-Argemone-aenea-prickly-poppy-#119-

A golden prickly poppy (Argmenone aenae)

#4

JPEG-4-Megachile-montivaga-F-in-flight-#

A silver-tailed petalcutter (Megachile montivaga) trimming prickly poppy petals

#5

Male Lithurgopsis littoralis cactus wood-brer bee - (c) Copyright 2019 Paula Sharp

A male Lithurgopsis littoralis cactus woodborer bee  

#6

A littoral cactus woodborer bee (Lithurgopsis littoralis) disappearing into the dense stamens at the center of a prickly pear blossom.

#7

Diadasia rinconis inside pricly poppy - (c) Copyright 2019 Paula Sharp

Male Diadasia rinconis "cactus bees"  resting together inside a golden prickly poppy 

#8

WJPEG-Melitoma-peering-from-esperanza-cr

A male Melitoma marginella peering from a fallen esperanza blossom after a storm

#9

Anthophorula compactula bee - (c) Copyright 2019 Paula Sharp

A compact Anthophorula (Anthophorula compactula) 

#10

Melissodes opuntiellus long-horned bee - (c) Copyright 2019 Paula Sharp

A male little prickly pear long-horned bee (Melissodes opuntiellus) 

#11

Cockerell, Melissodes opuntiella, Melissodes opuntiellus, Can Ent Vol 35 (1897)

Cockerell's 1911 description of the little prickly pear bee 

#12

WJPEG-Striped-Bee-on-Prickly-Pear-Facing

A female Diadasia rinconis cactus bee inside a prickly pear blossom

#13

WJPEG-Opuntia-engelmannii-Prickly-Pear-F

A Texas prickly pear cactus blossom (Opuntia engelmannii)

#14

Aztec sweat bee - (c) Copyright 2019 Paula Sharp

An Aztec sweat bee (Aughochlora azteca) emerging from a prickly pear blossom

#15

A Tepanec long-horned bee (Melissodes tepaneca), a generalist pollinator that feeds occasionally on prickly pear

#16

Osmia subfasciata mason bee - (c) Copyright 2019 PaulaSharp

A blue mason bee (Osmia subfasciata) harvesting nest materials bus from a Texas prickly pear cactus  

#17

Diadasia rinconis chimney bee - (c) 2019 Paula Sharp

A male Diadasia rinconis cactus bee negotiating the petal of a cactus flower

#18

A littoral cactus woodborer inside a Texas prickly bear blossom

Paula Sharp is a photojournalist and the author of the national bestseller Crows over a Wheatfield and four other novels.  She has taught writing at Yale, Bryn Mawr and Weslyen University in Connecticut.  She and photographer Ross Eatman are the creators of the well-travelled website Wild Bees of New York and of the new website Wild Bees of Texas, which documents bees of the National Butterfly Center.  An exhibit of Sharp & Eatman’s photographs of bees is currently on a National tour.

All Photos and text (c) Copyright 2019 Paula Sharp.