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Darwin Correspondence Project

From Fritz Müller   [c. January 1874]1

For some years I have been engaged in studying the natural history of our Termites, of which I have had more than a dozen living species at my disposition.2 The several species differ much more in their habits and in their anatomy than is generally assumed. In most species there are two sets of neuters, viz., labourers and soldiers; but in some species (Calotermes Hg.) the labourers, and in others (Anoplotermes F.M.) the soldiers, are wanting.3 With respect to these neuters I have come to the same conclusion as that arrived at by Mr. Bates, viz. that, differently from what we see in social Hymenoptera, they are not modified imagos (sterile females), but modified larvæ, which undergo no further metamorphosis.4 This accounts for the fact first observed by Lespès, that both the sexes are represented among the sterile (or so-called neuter) Termites.5 In some species of Calotermes the male soldiers may even externally be distinguished from the female ones. I have been able to confirm, in almost all our species, that fact already observed by Mr. Smeathman a century ago, but doubted by most subsequent writers, that in the company of the queen there lives always a king.6 The most interesting fact in the natural history of these curious insects is the existence of two forms of sexual individuals, in some (if not in all) of the species. Besides the winged males and females, which are produced in vast numbers, and which, leaving the termitary in large swarms, may intercross with those produced in other communities, there are wingless males and females, which never leave the termitary where they are born, and which replace the winged males or females, whenever a community does not find in due time a true king or queen. Once I found a king (of a species of Eutermes) living in company with as many as thirty-one such complemental females, as they may be called, instead of with a single legitimate queen. Termites would, no doubt, save an extraordinary amount of labour if, instead of raising annually myriads of winged males and females, almost all of which (helpless creatures as they are) perish in the time of swarming without being able to find a new home, they raised solely a few wingless males and females, which, free from danger, might remain in their native termitary; and he who does not admit the paramount importance of intercrossing, must of course wonder why this latter manner of reproduction (by wingless individuals) has not long since taken the place through natural selection of the production of winged males and females. But the wingless individuals would of course have to pair always with their near relatives, whilst by the swarming of the winged Termites a chance is given to them for the intercrossing of individuals not nearly related. I sent to Germany, about a year ago, a paper on this subject, but do not know whether it has yet been published.7

From Termites I have lately turned my attention to a still more interesting group of social insects, viz., our stingless honey-bees (Melipona and Trigona).8 Though a high authority in this matter, Mr. Frederick Smith, has lately affirmed, that “we have now acquired almost a complete history of their economy,”9 I still believe, that almost all remains to be done in this respect. I think that even their affinities are not yet well established, and that they are by no means intermediate between hive- and humble-bees, nor so nearly allied to them, as is now generally admitted. Wasps and hive-bees have no doubt independently acquired their social habits, as well as the habit of constructing combs of hexagonal cells, and so, I think, has Melipona. The genera Apis and Melipona may even have separated from a common progenitor, before wax was used in the construction of the cells; for in hive-bees, as is well known, wax is secreted on the ventral side: in Melipona on the contrary, as I have seen, on the dorsal side of the abdomen; now it is not probable, that the secretion of wax, when once established, should have migrated from the ventral to the dorsal side, or vice versâ.

The queen of the hive-bee fixes her eggs on the bottom of the empty cells; the larvæ are fed by the labourers at first with semi-digested food, and afterwards with a mixture of pollen and honey, and only when the larvæ are full grown, the cells are closed. The Meliponæ and Trigonæ, on the contrary, fill the cells with semi-digested food before the eggs are laid, and they shut the cells immediately after the queen has dropped an egg on the food. With hive-bees the royal cells, in which the future queens have to be raised, differ in their direction from the other cells; this is not the case with Melipona and Trigona, where all the cells are vertical, with their orifices turned upward, forming horizontal (or rarely spirally ascending) combs. You know that honey is stored by our stingless bees in large, oval, irregularly clustered cells; and thus there are many more or less important differences in the structure, as well as in the economy, of Apis and Melipona.

My brother, who is now examining carefully the external structure of our species, is surprised at the amount of variability, which the several species show in the structure of their hind legs, of their wings, &c., and not less are the differences they exhibit in their habits.

I have hitherto observed here 14 species of Melipona and Trigona, the smallest of them scarcely exceeding 2 millimetres in length, the largest being about the size of the hive-bee. One of these species lives as a parasite within the nests of some other species.10 I have now, in my garden, hives of 4 of our species, in which I have observed the construction of the combs, the laying of the eggs, &c., and I hope I shall soon be able to obtain hives of some more species. Some of our species are so elegant and beautiful and so extremely interesting, that they would be a most precious acquisition for zoological gardens or large hot-houses; nor do I think that it would be very difficult to bring them to Europe and there to preserve them in a living state.

If it be of some interest to you I shall be glad to give you from time to time an account of what I may observe in my Melipona apiary.

Believe me, dear Sir, &c., | Fritz Müller

Footnotes

The date is established by the relationship between this letter and CD’s letter to Nature, 11 February 1874, with which he enclosed this letter. Post from Brazil usually took about six weeks.
Müller began studying termites around 1869. Müller sent a description of a termite nest to Hermann August Hagen on 30 August 1869; Hagen presented it at a meeting of the Boston Natural History Society on 29 January 1870 (F. Müller 1870). Most of Müller’s research was done after he received Hagen’s monograph on termites in autumn 1871 (Hagen 1855–60; see Möller ed. 1915–21, 2: 199).
Calotermes is a synonym of Kalotermes, a genus of the family Kalotermidae, dampwood termites. Anoplotermes is a genus of Termitidae, higher termites.
Henry Walter Bates compared the mode of growth or metamorphosis of ants and termites in Bates 1863, 2: 61–2.
Charles Lespès made this observation in his study of the structure and habits of Termes lucifugus (now Reticulitermes lucifugus; see Lespès 1856, p. 233).
Henry Smeathman had described king and queen termites and their relative sizes (the queen about a thousand times larger than the king) in his ‘Account of the termites, which are found in Africa and other hot climates’ (Smeathman 1781, pp. 151–3). He noted that because of their large size, neither king nor queen could exit the royal chamber. His description was based on his observations of Termes bellicosus (now Macrotermes bellicosus), although he mentioned other species as well (see ibid., p. 147).
Müller completed the third part of his study on termites in November 1872 and it was published in 1873 in the Jenaische Zeitschrift für Naturwissenschaft (F. Müller 1873–5, pp. 451–63). Müller argued that the two forms of sexual reproduction were accounted for by CD’s theory, expressed in Variation 2: 144: ‘the crossing of animals and plants which are not closely related to each other is highly beneficial or even necessary’; he likened the reproductive strategy of termites to the existence of open and cleistogamic flowers (modified forms in which the flower never opens and only self-fertilisation is possible) in some plants (F. Müller 1873–5, pp. 458–9).
Müller’s interest in stingless honey bees began while he was reading proofs of his brother Hermann Müller’s book on the fertilisation of flowers by insect agency (H. Müller 1873) and initially he tried to find the bee species mentioned in that work. He sent specimens of some Brazilian bees to Hermann who sent them on to Frederick Smith for identification (letter from Fritz Müller to Hermann Müller, 15 December 1872, Möller ed. 1915–21, 2: 208–10). In January 1873, Fritz sent around forty bee specimens, including nine species that he described as in the genera Melipona and Trigona (letter from Fritz Müller to Hermann Müller, 29 January 1873, Möller ed. 1915–21, 2: 214–18). For more on Fritz Müller’s work on stingless honey bees, see Möller ed. 1915–21, 2: 208ff., and West 2003, pp. 178–82.
Smith made this comment in his paper ‘Observations on the economy of Brazilian insects, chiefly Hymenoptera’ (F. Smith 1868, p. 134).
Müller later referred to the species as Trigona limào (see letter from Fritz Müller, 20 April [1874] and n. 19).

Bibliography

Bates, Henry Walter. 1863. The naturalist on the River Amazons. A record of adventures, habits of animals, sketches of Brazilian and Indian life, and aspects of nature under the equator, during eleven years of travel. 2 vols. London: John Murray.

Hagen, Hermann. 1855–60. Monographie der Termiten. Linnea Entomologica 10 (1855): 1–144, 270–325; 12 (1858): 1–342; 14 (1860): 73–128.

Lespès, Charles. 1856. Recherches sur l’organisation et les mœurs du termite lucifuge. Annales des sciences naturelles. Zoologie 4th ser. 5: 227–82.

Müller, Fritz. 1873–5. Beiträge zur Kenntniss der Termiten. I. Die Geschlechtstheile der Soldaten von Calotermes. II. Die Wohnungen unserer Termiten. III. Die ‘Nymphen mit kurzen Flügelscheiden’ (Hagen), ‘nymphes de la deuxième forme’ (Lespès). Ein Sultan in seinem Harem. IV. Die Larven von Calotermes rugosus Hag. Jenaische Zeitschrift für Naturwissenschaft 7 (1871–3): 333–58, 451–63; 9 (1875): 241–64.

Müller, Hermann. 1873. Die Befruchtung der Blumen durch Insekten und die gegenseitigen Anpassungen beider. Ein Beitrag zur Erkenntniss des ursächlichen Zusammenhanges in der organischen Natur. Leipzig: Wilhelm Engelmann.

Smeathman, Henry. 1781. Some account of the termites, which are found in Africa and other hot climates. In a letter from Mr. Henry Smeathman, of Clement’s Inn, to Sir Joseph Banks, Bart. P.R.S. [Read 15 February 1781.] Philosophical Transactions of the Royal Society of London 71: 139–92.

Smith, Frederick. 1868. Observations on the economy of Brazilian insects, chiefly Hymenoptera, from the notes of Mr. Peckolt. [Read 3 February 1868.] Transactions of the Entomological Society of London (1868): 133–6.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.

West, David A. 2003. Fritz Müller. A naturalist in Brazil. Blacksburg, Va.: Pocahontas Press.

Summary

Agrees with Bates that neuter termites are not modified imagos (sterile females), but modified larvae (of both sexes).

Systematic relations of stingless honey-bees (Melipona and Trigona) are not yet well established.

Letter details

Letter no.
DCP-LETT-9281
From
Johann Friedrich Theodor (Fritz) Müller
To
Charles Robert Darwin
Sent from
unstated
Source of text
Nature, 19 February 1874, p. 309

Please cite as

Darwin Correspondence Project, “Letter no. 9281,” accessed on 15 October 2019, https://www.darwinproject.ac.uk/letter/DCP-LETT-9281.xml

Also published in The Correspondence of Charles Darwin, vol. 22

letter