Phil Rau.
The Biology and Behavior of Mining Bees, Anthophora abrupta and Entechnia taurea.
Psyche 36:155-181, 1929.

Full text (searchable PDF, 6796K)
Durable link: http://psyche.entclub.org/36/36-155.html

The following unprocessed text is extracted from the PDF file, and is likely to be both incomplete and full of errors. Please consult the PDF file for the complete article.

PSYCHE
VOL. XXXVI SEPTEMBER, 1929 No. 3
THE BIOLOGY AND BEHAVIOR OF MINING BEES, ANTHOPHORA ABRUPTA AND
ENTECHNIA TAUREA.
BY PHIL RAU
Kirkwood, Mo.
Introduction
This paper deals with the behavior and biology of two species of mining bees, Anthophora abrupta and Entechniu taurea, with brief notes on Anthophora raui. Large colonies of these three bees carried on their mining operations in a sheltered clay bank at Wicks, Mo. All three species were also important factors in the life of this microcosm (the clay bank community), and their relations, interrelations and reactions to environment have been studied and re- ported in a paper entitled "The Ecology of a Sheltered Clay Bank : a Study in Insect S~ciology."~ In making an ecological study of that kind, one often faces difficulty in deciding just which data to publish under the title ecology, and which rightfully belongs to biology or behavior. Hence I tried to sift out for that paper the data on ecology, and all the remaining material, which more properly belongs to biology and behavior, is published herewith. Since the reader may not always agree with me in my arbitrary classification of data, and since I have tried not to repeat in this paper the data already published under the title "Eco- logy," I can only recommend that he read the Academy of Science article in connection with the present one. 1 Trans. Acad. Sci. St. Louis, 25:159-276. 1926.



================================================================================

156 Psyche [September
The clay bank (fig. 2) at which these bees (figs. 5, 6 and 7) were nesting, faced the east, where it received the morn- ing sun, and was protected from the weather by the porch above it.
THE TURRET-BUILDING BEE, Anthophora abrupta. Anthophora abrupta makes no secret of its presence. They are neither timid nor aggressive, but they certainly are self-reliant. Their presence is easily and quickly de- tected by two prominent indicators, the bees themselves, and the conspicuous nests which they build. A glance at the picture (fig. 5) will convey to the reader some idea of how conspicuous they are as they noisily swing their ponderous bodies to and fro on the wing, arrive home and scramble into their burrows or come tumbling out headlong and dash off into the sunny fields, with all the exuberance of boys just out of school. They have none of the shy, stealthy ways of maneuvering, whereby some of the smaller and daintier varieties of bees and wasps hold their own in a competitive world. They go boldly and fearlessly about their work, and soon construct nests which are likewise prominent. While many species of solitary wasps and bees try in some way to conceal the location of their burrows, these construct large mud chimneys over their nests, made from the clay dug out of the burrows (fig. 1). Since they work in colonies, or more correctly remain to build on the site where they were born, the result is a very conspicuous village, sometimes a very crowded and busy town of these masonry turrets as shown in profile in fig. 8. At a busy season when many of these huge bees are bustling about with very audible hum and zip, the entire village with its many wonderful towers and industrious citizens form a spectacle which is in itself quite capable of overawing any but the most unemotional individual.
In 1917 the Anthophora abrupta first appeared on June 25th. In 1918, the spring was warmer and they were out and at work much earlier, and the size of the chimneys in- dicated that they must already have been at work some days before I discovered them on May 28th.




================================================================================

FIG. I
Fig. 1, The work of Anthophora abmpta. Turrets built over their nests. Fig. 2. The clay bank under the porch where the three species of mining bees nested.




================================================================================

158 ' Psyche [September
In the spring of 1921 the males were found flying on May 27th, when they were frequently seen on the flower- buds of the rambler roses. Often they seemed to be trying to bite their way into the buds. At evening they were often seen to climb to the top of a grass-blade, grasp the tip firmly in their jaws and go to sleep. Fig. 3 shows a male sipping sugar water from a piece of cotton.
Fig, 3. The male of Anthophora abrupta.
I have never seen mating occur at the bank, and I have often wondered if they do not go elsewhere for the purpose of meeting the females. At a point about one hundred yards distant, on a hill side facing the eastern sun, I repeatedly saw a number of males hovering and flitting over a barren spot about three feet square covered with old rusty slag. At first I suspected that this was the place of their courtahip- dances, but I failed ever to discover a female there. Instead the males were often found devoting their attention to the ruskovered ashes, to which they clung with their jaws. That reminded me how the females of their species at Man- chester, Mo., during the previous summer had shown aston- ishing persistence in eating the rust from an old iron barrel- hoop and rusty fence-wire. Perhaps these males merely went to this bed of cinders to get their supply of mineral salts while the females were emerging and prospecting for burrows. This habit of licking rusty objects was not merely a casual occurrence but a purposeful and persistent activity ; it elsewhere attracted the notice of my companion, who



================================================================================

19291 Biology of Mining Bees 159
suggested that carnivouous insects can derive their mineral salts from the blood and juices of their food, but these mining-bees are nectar feeders; hence it is possible that they may need to obtain their necessary mineral salts by some such direct "methods as this.
On the next day the persimmon blossoms were beginning to open and already the bees had turned their attention thither; within three or four days more they were in- tensely active at this new task. In this short time, less than a week, the males had disappeared. Thus in a short while, and in keeping with the rapidity with which this species lives and does things, the males had come and gone, and the females remained buzzing at their new work. They hummed and danced in the sunlight in front of the bank; this activ- ity, however, was not a courtship dance such as occurs in other insect species, but merely the industrious search in flight before the face of the bank as each bee tried to dis- tinguish her own burrow. It was not a simple task at so early a time in the season, and it gave rise to more commo- tion than later when the bees had had more experience. If one singled out an individual in the crowd and continuously followed it with the eye, one would see that it finally plunged into an opening, sometimes to remain and sometimes to come precipitously tumbling out again and try another. It is little wonder that the returning bees must spend some time in distinguishing their own nest among hundreds or even thousands of burrows, but my observations have sub- stantiated my expectation that later in the season, when the turrets were nearly all built, they would consume less and less time in this orienting dance as they learned more readily to distinguish their own nests among- the hundreds in the group. I have stated elsewhere that when these bees came home late in the evening, their hovering in front of the nests was much prolonged, owing to their difficulty in finding their way in the fading light. A number of the larger turrets and their occupants were marked ; these were watched in comparison with the rest of the population. It was soon apparent that those with large turrets found their homes with much less hesitation than the turretless ones. Hence I sometimes wonder, since I have never yet learned



================================================================================

160 Psyche [September
the utility of these chimneys, whether they might not be built to serve as landmarks for the returning bees. The variation in the size, shape and position of these turrets was much more apparent than that of the mere apertures in the bank. The turrets ran in various directions; some were horizontal, some tilted a little downward, others were at various angles toward north and south. There seemed to be no plan or scheme of direction, except that none were seen with an upward tilt, but the points of the compass were utterly disregarded, (see figs. 1, 4, and 8) and so far I have been unable to discover any factor, light, convenience, effi- ciency, or anything else, that could determine the direction in which these chimneys curved as they grew. Their dia- meter, (fig. 11) about 1/? inch outside measurement, was fairly uniform for the entire colony, but their length varied from nothing to three inches, the greatest number of finished ones measuring about two and one-half inches in length. None of the tubes were found to be closed either at the base or at the orifice of the chimney; the entire channel leading down to the cells was in every case hollow, with an open groove for its full length along the top. The bees did not tear down the chimney and utilize the mate- rial for tunnel-filling as do the Odynerus geminus wasps,l nor did they even seal the tunnel with a thin wall at the surface of the ground. The tunnels were tor- tuous and hard to follow, owing to the closeness of the nests and the extreme hardness of the clay. One tunnel was opened which slanted downward, then upward, forming a letter "V" with a total length of five inches. Another, which had a two-inch tube, penetrated the bank to a depth of six and a quarter inches, following a zig-zag course, and terminated in the usual pocket. This mother evidently had lost her nest or had become lost herself before the nest had been completed or used. This was not the only case of this failing; in a number of cells we found this same condition. But these abrupta went further than merely to dig a burrow in the ground and provision it, as do so many species of their kind. Deep down within the tunnels in the 1 Wasp Studies Afield, p. 299-312, 1918.



================================================================================

19291 Biology of Mining Bees 161
solid clay they built distinct cup-shaped or thimble-shaped cells in which they placed the store of prepared pollen and the egg, and then individually sealed them, in this way obviating the necessity of sealing the outside or main tunnel to exclude intruders. This method gave excellent protection against injury by violence and the weather, for the cells containing the eggs or larvae were heavier than the little pots which the potter-wasps attach to twigs, and they equalled in thickness and warmth the mud walls of Trypox- ylon politurn and they had in addition the protection of the deep burrow. These cells were oval, %, inch in length, placed close together and were varnished on the inside with some special waxy substance. Fig. 12 shows a lump of mud with these brood pots.
The bees continued to extend the tunnels by excava- tion and enlarge the chimneys by addition. They brought water from a mud-puddle in the road fifteen feet dis- tant, carrying the load in the gullet. With a portion of the water they would wet the hard, yellow clay, remove a mouthful of it, back out and apply it to the last ring in the chimney. The bees would carry the mud under the thorax with the front pair of legs, while the two hind pairs furnished locomotion; as the bee backed out of the nest to the opening, the ball of mud was passed to the hind legs, and she now held her footing with the front legs while with hind legs she slapped the mud onto the last layer and with many active thumps with the tip of the abdomen, punched and beat it into shape. "Punched" is really the right word correctly to describe the gesture. Entechnia taurea does similar work with much finer precision; in that species the bee divides the ball of earth into two portions, applies the first part to the center of the tube at the bottom, and care- fully smooths and works it on the left side almost to the top; then she applies the second portion in the same way at the base and works it up on the right side. The result of this method is that, either through the builder having insufficient material, or from some other cause, there remains a split or open groove down the full length on the upper median side of the tunnel, where the two halves of the load of mud fail by only a narrow margin to meet.




================================================================================

162 Psyche [September
The bee here considered, Anthophora abrupta also left an opening along the top of most of the chimneys, (figs. 4 and II)1 but here it was not due to the method of building fol- lowed by E. taurea, for A. abrupta, applied her load of mud wherever she happened to strike the edge, on the bottom or sides, and the job of spreading it was quickly done. In Fig. 4. A close-up view of the turrets over the nests of Anthophora abrupta.. this species the chimney was somewhat greater in diameter, and it was rougher on the outside, but the interior surface was very smooth and neat. Sometimes in her hurry to apply the mud, the bee dropped it; at other times she might be seen brushing out loose, moist materials by kicking them backwards, probably the crumbs or scraps that had dropped 1 Fig. 4 and 1 show these openings very distinctly, while Fig. 11 does not show so many, because in the latter figure they were inverted when the photograph was made. In most of the turrets in Fig. 11 we see the bottom side,




================================================================================

19291 Biology of Mining Bees 163
from the walls in the process of biting out the hard clay, or the scraps that dropped while she fashioned her thimble- like cups.
Unlike the homes of some species, this gallery was roomy enough that the owner could turn around in it, for while she always backed out when she emerged with her load of mud, she did just the opposite when she came out for water, for then she always came out head first and dashed away. One singular feature occurred in the great majority of individuals observed; when they had used up the water, and had applied the last load of mud to the turret, they did not realize their need and fly directly out and away for more water, but re-entered the hole as usual, sometimes stayed in a few minutes and then came out head-first and flew away to the watering place. This might be due to the fact that the bee did not know that the water was gone and must have as a stimulus the experience of biting out the dry soil to arouse her inclination to go for more water. On the other hand, it might be that she entered the hole only to turn around so as to leave head-first, instead of tumbling out backwards as when she had applied her mud. The bees, when they had arrived at the water, did not alight upon the surface as do certain wasps, by spreading their legs, but landed on the soft mud on the margin, and with the long tongue protruding lapped it up. They were not bound by instinct even to go to the same place regularly for water, for one year after a rain many were seen availing themselves promptly of the temporary convenience and gathering the drops from the vegetation very near to their doors, instead of going to their customary place.
The round trip for water consumed from one-fourth to one-half minute, and the number of pellets of mud that could be carried out with each mouthful of water was inter- estingly varied. One bee which was watched for one hour, from 2:03 to 3:05 p.m. made twelve trips for water, and removed forty-seven balls of mud. When one considers that the mud was not only excavated, but was built into the chimney, one feels that this is a good hour's work for so small a creature. One gulletfull of water would remove 2 to 5 balls of earth, the greatest frequency being 4 ; this num-



================================================================================

164 Psyche [September
ber occurred six times, five loads occurred three times, three loads twice, while in only one instance did she carry only two loads for one mouthful of water.
Another bee working from 2 :03y2 to 3 :01 p.m. made twelve trips, and carried out 2, 1, 2, 2, 3, 5, 2, 5, 5, 2, 1, 2 loads, or thirty-two balls of earth in 5734 minutes; she was not quite as industrious as the first one. A third one also made twelve trips in the same hour, and carried out 1, 7, 2, 2, 0, 4, 3, 2, 2, 6, 2, and 2, totaling 33 loads. This is sufficient to show that there is no regularity in the number of balls removed.
I was unable to ascertain whether the entire amount of water was ejected at one time and the dirt thereby softened, or whether, as in the wasp Odynerus geminus, only a little water at a time was disgorged upon the spot, the mud bitten out, and then another spot moistened.
By the middle of July, I found the Anthophora, abrupta, had entirely disappeared, and some of the chimneys were dropping to the ground beneath. When these bees had completed their work, neither the chimney nor the tunnel was plugged up, and, since the former often dropped through disintegration soon after the work was completed, it seemed that they could serve no utilitarian purpose ex- cepting during nidification. Some of the turrets were built so well that they withstood the winter, remaining intact for a year or more.
Chalcid parasites of the genus Monodontomerus were abundant about the bank, loitering about the holes, wait- ing for the provisioning to take place. They were indolent, and did not even evade when one attempted to take them in the fingers. Many of the empty pupal cases of Anthophora obrupta harbored several of these live chalcids. In one cocoon I found twenty living pupae of this parasite on June 28th, and since the adults were plentiful there a month earlier, the finding of the pupae at that date indicated a second generation. On June 24, 1920, several cells of this mining-bee were brought indoors. They were not examined until September 2, when several chalcid parasites emerged. To be exact, there were 109 females and 39 males from four cells, or an average of 35 to each cell. Of the other



================================================================================

19291 Biology of Mining Bees 165
nine cells collected, three had dead larvae, five contained dried-up balls of food, and one harbored a parasitic cuckoo- bee.
The "open door policy" of this species sometimes brought its trouble too. Not infrequently an animated fight was to be seen between two females, one evidently trying to usurp the burrow that had been made by another, and often dead bees were found at the foot of the bank. Occasionally a dead one was found in the burrow, and in all probability a second mother, in appropriating the nest, cleared the dead body out with the other rubbish. Frequently, however, the fights appeared quite alarming without proving fatal. One pollen-laden mother was seen backing out of her hole with the front leg of an intruder in her mandibles. The visitor showed no fight, but resisted with all her might; at the foot of the hole, every little gain that the rightful owner made was offset by the intruder pulling her back. At last the intruder lost her hold, and as they went tumbling to the ground they engaged in a pugnacious embrace. Needless to say that the rightful owner lost most of her load of pollen, which deluged the face and head of her antagonist. Another pair was locked in deadly embrace for over twenty minutes, and there seemed no probability of their separating soon. They were so intent that they were unaware of the fact that they were being pushed into a test-tube. After five minutes more of violent struggling in this novel place, they lost their grip for a moment and separated, and when they were liberated, they both flew into the air, little disconcerted by the ordeal.
A. abrupta made nests either with or without turrets, and the turret-making activities were directly correlated with water conditions. They required water in abundance, and when it was plentiful, so too were the turrets; in droughty years they struggled on with few and small or no turrets, and their nesting activities were much reduced. If they had to struggle on with a small drop of water, they consumedmuch more time in mining than when they could be generous with the water and thoroughly and quickly wet the hard clay. It was pathetic to see the mother back out of her hole with a load of slightly moist soil instead of a load of wet mud;



================================================================================

166 Psyche [September
when she attempted to work it into the turret it would crumble and fall to the ground. The size of the population, it seemed to me, was just as much regulated by the amount of water available as by the number of parasites, for in 1922, when hundreds of bees were at work and the fewest turrets were made, the official statement from the local weather bureau at St. Louis showed that the precipitation for the five months, May to September inclusive, was the least recorded in 85 years.
In another colony, in a different locality, the nests were also built without turrets, but in that case the deficiency was due to lack of clay instead of water. Here the mothers were nesting in the disentegrating mortar of an old stone chimney. Despite the fact that so little turret material was available, and no normal chimneys were made, a good many of the tunnels had a very small ring or collar at the opening. This bee was almost contemporaneous with A. raui (fig. 6) ; however, interbreeding of the two species was not pos- sible. Careful observations in 1922, showed that A. abrupta emerged from May 30th to June Znd, and by June 3rd all the males were dead. A. raui did not appear until June loth, a week after the males of A. abrupta were gone. This made it impossible for the males of A. abrupta to fertilize the females of A. raui and since the females of A. abrupta had already been fertilized when the A. r& emerged, a second fertilization was improbable. In 1929, the A. abrupta population waned on about July 2, and the A. raui about July 12.
Since A. raui Rohwer is a new species, reported so far only from this particular clay bank, it would be fascinating, if justifiable, to surmise that this habitat is the cradle of the species, an offshoot from A. abrupta.
We may cite for comparison some observations on other species of this genus in various localities by different in- vestigators.
Sharp1 says Anthophora is one of the most extensive and widely distributed of the genera of bees. He also points out that Friese has made the discovery that A. personata2 at 1 Insects. Pt. 11, p. 33, 1899.
2 A. personata is now called A. fulvitarsis Brulle. (fide T. D. A. Cockerell).



================================================================================

19291 Biology of Mining Bees 167
Strasburg takes two years to accomplish the life cycle of one generation. "Some of the species make burrows in cliffs and form large colonies which are continued for many years in the same locality."
Say, in referring to the habits of European A. parietina, says that this species digs a hole in a clay bank and that the entrance consists of a cylinder extending downward more than an inch in length and made of small pellets of earth compacted together, rough on the exterior and smooth within.
Hungerford and Williams1 made note of the nesting habits of A. occidentalis, which they call the "larger