Observations on the So-called Trumpeter in Bumblebee Colonies.
Psyche 30(5):146-154, 1923.
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146 Psyche [October
OBSERVATIONS ON THE SO-CALLED TRUMPETER IN BUMBLEBEE C0LONIES.l
College of Liberal Arts, Boston University. About 250 years ago, the Dutch painter Goedart (1685) published a comprehensive treatise2 on insects, volume 2 of which contains a unique and probably the oldest account of the life-history and habits of bumblebees. The account seems to be based almost entirely on the author's own observations, and is of interest chiefly because of its many naive anthropomor- phisms. Thus, for example, Goedart (pp. 242-245) states that the members of a bumblebee colony, besides keeping a "king" like the honeybees, also have another individual among them which mounts to the top of the nest each morning about 7 A. M., and, like the bugler in the army, calls his companions to work by rapidly vibrating his wings, thereby producing a noise not unlike that of a drum. This performance, according to Goedart (p. 245), lasted for about a quarter of an hour each morning, and was observed repeatedly, not only by him, but also by others. About seventy-five years later, Goedart's (1685) observation was con- firmed by the French Abbe Noel de Pluche (1764)3, but de
Pluche (p. 185) found t,hat the "drummer", or "trumpeter", which he had under observation, called his companions to work at 7.30 A. M., instead of 7.
No one seems to have questioned this fantastic story until 1742 (about 75 years after the story originated), when the great French engineer and entomologist, Reaumur (pp. 1-30), published his observations on bumblebees. Although this famous scientist had a large number of bumblebee colonies under observation, he was unable to discover any such behavior as that described 1Contributions from the Entomological Laboratory of the Bussey Institution, Harvard University, No, 225.
2The first edition of this work appeared from 1662-1669, both in Dutch and in Latin. It was later also translated into English (1682) and French (1700). 3Accordine to Sladen (1912, p. 48). other editions of this work appeared as early as 1732 Translations into English (by Samuel Humphreys (1740). German (1746), and Spanish (1754); made this comprehensive workaccessible to alarge number of readers outside of France.
19331 Observations on the So-called Bumblebee Trumpeter 147 by the earlier observers, and therefore came to the conclusion that Goedart's (1685) "trumpeter" story was a fable. R6aumur7s (p. 30) opinion in this matter naturally carried much weight, being accepted by such eminent entomologists as Kirby and Spence (1818, p. 384)) and dealt the bumblebee "trumpeter" a blow which was effective for almost 150 years, when Goedart's (1685) story was again revived by the well-known Austrian bumblebee student Hoff er (1881, 1882-83). Being acquainted with the contradictory claims of Goedart (1685) and Reaumur (1742)) Hoffer (1882-83, p. 23) tried for a number of years to find a "trumpeter" among the numerous bumblebee colonies which he had under observation, but his efforts were unsuccessful until the summer of 1881. On July 7 of that year, Hoffer (p. 23) obtained a strong colony of Bremus (Bombus) ruderatus which he placed in a window facing southeast. Early the following morning, Hoffer7s (p. 24) attention was suddenly attracted by a peculiar humming in the new colony, and, upon investigating, he found that the sound was produced by one of the larger bees which was perched on the waxen envelope of the nest and was vigorously, but uniformly vibrating her wings. Overjoyed at having rediscovered the long-sought 'trumpeter," Hoffer (p. 25) roused his wife and children, and later also called in the neighbors, to witness the interesting per- formance. However, Hoffer's (1 882-83) "trumpeter", or "trump- eterette" as she ought to be called, evidently was some- what of a slave-driver, and rat,her persistent, as compared with those of Goedart (1685) and de Pluche (1764), for "with painful regularity" she called her companions to work every morning shortly after three o'clock, and continued her "trumpeting" for about an hour. Hoffer (p. 25) now became interested to know what would happen if he removed the "trumpeter" from the colony, and, on doing so, found that thereafter t'he "trumpeting" was performed by another member of the colony, although about an hour later than before. As the colony grew smaller toward the end of the summer, the activities of the "trumpeter" became more and more irregular. This, and the fact that one of his former students claimed to have heard a "trumpeter" in a colony of Bremus lapidarius, led Hoffer (1882-83, pp. 25, 26) to the
148 Psyche [October
conclusion that only Bremus ruderatus, and perhaps some other "hypogeic" species, have "trumpeters," but only while the colonies are strong.
Hoffer's (1882-83) confirmation again brought Qoedart's (1685) "trumpeter7' story into good repute among biologists for a period of more tlhan twenty years. With apparently the single exception of Perez (1889)) it was accepted-in most cases after personal verification-by Firtsch (cf. Hoff er, 1882-83, p. 25)) Kristcf (1883)) Barter (1890), Sharp (1899)) Marshall (1902)) and Bcngtsson (1903). Perez (p. 117)) while not in the least doubting the general correctness of Hoffer's (1882-83) ob- servations, rejected the latter's interpretation by pointing out (1) that there is little sense in having a "trumpeter" unless he be the first one to rise, and (2) that the sound produced by the 'trumpeter5' is of no use whatever, as far as rousing the colony is concerned, since (according to Perez) bumblebees, like honey- bees and ants, are completely deaf. Perez (1889) then offers his own explanation. After expressing the opinion that the bumble- bee "trumpeter" fulfills no social function, and that the "trump- eting" is probably done for his own benefit, Perez (p. 117) suggests that the "trumpeters" in bumblebee colonies, like the so-called ventilators among honeybees, are newly-hatched individuals which are training their wing muscles for the long flights which they will soon make. However, as we have already seen, Perez7 (1889) theory, although more plausible than that of Qoedart (1685), seems to have made little or no impression upon contemporary biologists.
Fourteen years after the publication of this theory, a third interpretation was offered by the well-known German bee student von Buttel-Reepen (1903, 1907). Unlike Perez (1889)) this author suggested that t5he bumblebee "trumpeter7' has the same social function as the ventilators in t'he honeybee colonyj4 4Since writing the above, I have discovered that a similar explanation was offered by Mr. J. Angus in a letter to Messrs. A. S. Packard and F. W. Putnam (cf. Packard (1868). 35 years before vor~ Buttel-Reepen published his interpretation. Mr. Angus' letter partly reads as follows: I have found the males [of Bremn-s (Bombus) va.ga.ns} plentiful near our garden fence, with a hole such as would be made by a mouse. They seem to be quite numerous. I was at-
tracted to it by the noise they were making in fanning at the opening. I counted at one time as many as seven thus employed, and the sound could be heard several yards off. Several males were at rest, but mostly on the wing, when they would make a dash among the fanners, and all would scatter and sport around. The workers seem to be of a uniform size, and fully as large as the males. I think the object of the fanning was to introduce air into the nest, as is done by the Honey-bees.
19231 Observations on the So-called Bumblebee Trumpeter 149 namely, to reduce the temperature, or to expel moisture or bad odors from the nest. Similar conclusions were reached by the Norwegian biologist Lie-Pettersen (1906). This new inter- pretation was accepted-in some cases after extensive experimen- tation-by Stierlin (1906)) Wagner (1907), Gundermann (1908), Lindhard (l912), and Sladen (1912).
However, within the last decade, Goedart's (1685) "trump- eter" story has found another adherent in Bachmann (1915, 1916). What is more, Bachman (1915) has discovered that the bumblebee "trumpeter", in addition to rousing tthe members of the colony in the morning, also attends to the "curfew" in the evening. This latter perfomance, Bachmann (1915, p. 87) describes as follows: "Urn 9 Uhr begann der Hiimmel- trompeter sein Abendlied. Es war ein langerer Ton, unterbrochen von einem Triller ahnlich wie wenn ein Tier im Kastchen fliegen wurde. Der Trompeter schlug aber nur, auf der Wabe stehend, die Flugel."
The activity of the bumblebee "trumpeter7' in the morning is described very vividly by Bachmann (1916, p. 103) in the following words: "Genau um 6 Uhr erhebt sich ein Sunimen im Nest, das ununt'erbrochen 2 Minuten dauert. Ich musste gleich
an den Hummeltrompeter denken, den Hoffer in einem Nest von Bombus ruderatus entdeckt hat.
Dreimal setzt niein Musikant
an, bis es lebendig wird und ein Tierchen zum Abflug erscheint. Urn 6.26 bringt ein geschaftiges Weibchen eine grosse Larve geschleppt und der Trompeter ubt unentwegt seine Kunst. Zuerst in gleicher Tonlage sunimend, werden, wenn es langer dauert, die Schwebungen hoher und tiefer, vibrierend, dann stossweise wie das Gerausch des Wagnerschen Hammers oder bei der Entladung elektrischer Funken, endlich wie ein langsamer Tromnielwirbel, bis der Ton etwas hoher wird und dann langsam erstirbt.
"Mitunter hore ich deutlich die Flugel schlagen und meine dabei, es fliege eine Hummel nahe am Kopf voruber. Dieses Wecken dauert von 6.44 bis 7.06, also 22 Minuten ohne Unter- brechung and ohne die geringste Storung meinerseits. Bis 8 Uhr hore ich noch dreimal einen kurzeren Ruf. Dann kriechen
150 Psyche [~ctober
gleich 3 Hummeln auf einnd aus dem Nestloch, nachdem mit Korbchen beladene im Tor vorher einpassiert waren und der Betrieb in der ~ummelburg kommt in regen Gang." These two passages would not have been written, had Bach - mann (1915, 1916) paid more attention to the literature of the preceding decade. As we have already seen, Bachmann's (1915, 1916) assertions were cont'radicted years before, by statements published by several authors, notably von Buttel-Reepen (1903), Lie-Pettersen (l906), Wagner (l907), Lindhard (19 12), and Sladen (1912). To these may be added certain observations and experiments of my own.
During the summers of 1921 and 1922, I had under obser- vation about sixty Bremus (Bombus) colonies belonging to ten5 of our thirteen New England species, and have frequently had occasion to observe the behavior which gave rise to the "trump- eter" story. That the fanning of these so-called trumpeters has to do with ventilat'ion of the nest, and not with rousing the colony, or the exercising of wing muscles, may be demonstrated very easily by exposing a bumblebee colony to the rays of the sun, a fact which was first pointed out by Lie-Pettersen (1906) and Wagner (1907). The conclusions which these two authors reached are corroborated by the following observations which were made during the summer of 1921.
Of the thirteen colonies which I had under observation during that summer, eleven were kept in windows facing south and the remaining two in a window which faced north. Like Lie-Pett'ersen (p. 18), I found that on every warm day, especially if the weather was sultry, one or more workers in each of the colonies on the south side of the building mounted to the top of the nest and began to fan shortly after the rays of the sun reached the nest-boxes. In a colony of Bremus impatiens, consisting of about 125 individuals, the number of fanning workers sometimes even increased t,o more than a dozen. As soon as the sun receded from their nest-box, these "trumpeters" discontinued their work, one after another, and crawled back into the nest. 5Brcrnzis afjinis, bimaculatus, fervidus, impatiens, pennsylvaukus, perplexus, separafus, fernarius, terricola , and vagans.
19231 Observations on the So-called Bumblebee Trumpeter 151 While this restless activity was in progress on the south side of the building, not a single bee, as a rule, was engaged in "trump- eting" in the two colonies which were kept on the north side, although one of the latter-also belonging to Brems impatiens- consisted of more than 450 workers. The exposure to the hot midday sun evidently did not agree with the bees, for the colonies on the south side of the building did not thrive nearly so well as those on the north side, and during the following summer all of my bumblebee colonies were therefore kept in shady situations. While "trumpeting" in a bumblebee colony is most pro- nounced when the nest is exposed to the rays of the sun on a hot day, it may, as is indicated by the observations of Goedart (1685)) de Pluche (1764)) Hoffer (1882-83)) Bengtsson (1903), and-Bach- mann (1915, 1916), also take place in the morning and evening, in fact, as Wagner (1907) has pointed out, at any time of the day. Thus, for example, I have occasionally found one or two workers fanning at various hours during the night, oven if the t'emperature outside was less than 70'.
In this case, as has been suggested by
von Buttel-Roepen (1903)) fanning no doubt has to do with the expulsion of moisture or disagreeable odors from the nest. Neither is it true, as Hoffer (1882-83), von Buttel-Reepen (1903), and Sladen (1912') assume, that "trumpeting" is resorted to only by species which have subterranean nests. Wagner (1907) found that Bremus muscorum, a European species which usually nests on the surface of the ground, resorts to fanning when the temperature of the nest gets too high, and this, as will be seen later, is also true of Bremus fervidus in this country. As already stated, Hoffer (1882-83) believed that small Bremus colonies have no "trumpeter." Wagner (1907) and Lindhard (1912), on the other hand, claim that small colonies also resort to fanning. In order to determine which one of these claims is correct, the following experiment was performed. At 2 P. M., on June 3, 1922, I exposed the next-box of a small colony (1 queen and 2 workers) of Bremus impatiens to the rays of the sun. Three minutes later, one of the workers crawled to the top of the nest and began to fan, and within another minute, the remaining worker and the queen appeared and assisted in this activity.
152 Psyche [October
Later in the summer, an experiment was also carried out to test Perez' (1889) theory, according to which the so-called bum- blebee trumpeters are newly emerged individuals which are exercising their wing muscles. On August 14th) at 1.30 P. M., I removed the board which shaded the nest of a queenless colony of Bremus fervidus so that the nest-box was exposed to the sun. The result was as follows: At 1.34, a worker appeared on top of the nest, and after crawling about a few seconds, began to fan vigorously. By 1.36 two more workers were engaged in this. work, and by 1.38, the number of "trumpeters" had increased to six. All of these "trumpeters", as the hardened pollen lump on the thorax showed6, were old bees which had done considerable foraging. Bremus fervidus usually nests on the surface of the ground, and hence this experiment incidentally also shows that Hoffer (1882-83)) von Butt'el-Reepen (1903)) and Sladen (1912) are wrong in assuming that only "subterranean7' species have "trumpeters."
Summary and Conclusions.
1. The so-called trumpeters in bumblebee colonies are bees which are engaged in ventilating the nest,. 2.
This ventilation is brought about by a rapid vibrat'ion of the wings and may take place at any time during the day or night. 3. Species which nest on the surface of the ground likewise make use of this method of ventilating their nests. 4. Ventilation by fanning is also resorted to by small bumble- bee colonies.
5. Perez' theory, according to which the so-called trumpeters in bumblebee colonies are newly emerged individuals which are exercising their wing muscles, is not founded upon facts.
Buchmunn, M. 1915. Biologische Beobachtungen an Hummeln. Mitteil.
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6The source of these pollen lumps will be discussed in connection with another paper.
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