Harvesting Ants and Trap-Door Spiders / Notes and Observations on Their Habits and Dwellings

by John Traherne Moggridge

There is much to be learned, I do not doubt, about the friends and enemies of harvesting ants; and another great desideratum is further information as to the parts of the world in which they are found and what causes may be assigned for the limitation of the habit.

What is the geographical distribution of the harvesting species, and what the geographical distribution of the habit? For instance, to quote Mr. F. Smith,[39] Atta structor, though not "found in England, is scattered over a great part of Europe, having occurred in France, Italy, Germany, Austria, Dalmatia, and Switzerland; it has also been found in Algeria" and Syria; and A. barbara is almost as widely spread. May we then conclude that these species are harvesters wherever they are found, and that they store seed in Germany and Switzerland as freely as they do on the shores of the Mediterranean? If this be really so, then Huber, whose attention was specially directed to this point, and a host of laborious and scrupulous observers of the Continent, have had the very fact under their eyes, though they have been at considerable pains expressly to deny it. I cannot think that this is likely, but it is a matter which could easily be settled by those who travel or reside in Germany, Northern France, or Switzerland.

[39] Mr. F. Smith, On Some New Species of Ants from the Holy Land, in Journ. Linnean Soc., London, vol. vi. p. 35.

It seems to me more probable, however, that they do store in the south, but not in the north; for all the difficulties which attend the preservation of the seed in the granaries in the south would be greatly increased in the wet climates of Northern Europe, and there, moreover, the greater cold would render the ants torpid almost throughout the winter, when food would not be required. But the question is plainly an open one. We may also ask why it is that only a very few out of the many species of ants which inhabit the shores of the Mediterranean should possess this habit of collecting seeds, and differ so widely in their manner of living, from their neighbours?

If we wish to put ourselves in the way to answer these queries, the first thing we should do would be to examine and compare the structure of the digestive organs and parts of the mouth in harvesters and non-harvesters, with a view to seeing whether there may not be some capital difference here.

These observations demand some skill in dissection and preparation, and in regretting that it has not been in my power to make them, I can only hope that some one more skilled than I am may undertake the subject.

It seems probable, that in warmer latitudes there are many conditions which favour the rapid increase of ants, so that a given tract of country in Southern Europe, for example, must have on an average more colonies to support than a similar tract in the north, and that to meet this increase of population, it has therefore become necessary for these creatures to seek their subsistence from as many and as dissimilar sources as possible. The fierce conflicts over booty both between rival nests of the same and of distinct species, tend to show that, even as things are, they frequently have to fight for their food.

Hitherto, as far as I have been able to learn, only nineteen true harvesting ants have been detected in the whole world, limiting this term to those species which make the collection of seeds the principal occupation of their outdoor lives, and are evidently in the main dependent upon this kind of food for subsistence.

Now if we compare these nineteen species of ants[40] together a very curious fact forces itself upon our notice—namely, that all of them are closely related, so much so that not only do all belong to the same division of ants (the tribe Myrmicineæ), but that with one exception (Pseudomyrma) all would have been placed by the great Fabricius in one genus, Atta, and the one exception is not far removed from it.

[40] These are Myrmica (Atta) barbata, from Texas and Mexico; Œcodoma (Atta) cephalotes, from Brazil and Mexico; Œcodoma (Atta) providens, from India; Œcodoma (Atta) diffusa, from India; Atta rufa, from India; Pheidole (Atta) megacephala, from South France; Atta barbara, from South France, Capri, and Algiers; Atta structor, from South France; and Pseudomyrma rufo nigra, from India.