Now these worker ants are destitute of stings, and I can only suppose that their power of combination, stronger jaws and more horny coats, have gained them this immunity. I remarked that the smaller lizards appeared to have some difficulty in dealing with the males and females which they captured, and would beat and pound them against the stones before devouring them, while the larger ones would often make but one mouthful of them, swallowing wings and all!
If it were not for this body-guard of workers it is difficult to see how the males and females in such situations could ever escape. It is also plain that if the worker harvesting ants were as liable to be seized and devoured as their winged companions, the species would soon become extinct, for they expose themselves more than ants ordinarily do, and their long provision-laden trains would be almost at the mercy of any enemy which could attack them without fear of results.[113]
[113] Speaking of the enemies of ants, I may mention having seen a young robin in England picking up and swallowing the workers of Formica nigra just as if they were crumbs. I knew that birds would eat the male and female ants, but I had thought the workers were exempt from their attacks, and, indeed, they must be so as a rule, for otherwise they would speedily become extinct.
Remembering this, it is interesting to note how differently the tiger-beetle (Cicendela) behaves when hunting the powerful harvesting ants and when preying upon the weak little Formica (Tapinoma) erratica; for, while it seizes the latter without taking any precautions, it is evidently more than half afraid of the former.
I have seen this beetle lying in wait near a train of structor or barbara ants, watching until some individual separated a little from the main body, when it would rush forward and make a snap at it, retiring again as quickly as it came. If the tiger-beetle fails to seize its prey exactly behind the head it will let it go again, and two or three ants are often thus cruelly mutilated before a single one is carried off.
No doubt the beetle has learned that if once this ant clasps its mandibles upon either antennæ or legs, nothing, not even death itself, will make it release its hold. It therefore tries to pin the ant in such a way that it cannot use its formidable jaws. Perhaps the habit of forming long compact trains may have been acquired by the ants partly with a view to guarding against attacks of this kind.
The colonies of the little F. erratica, on the other hand, apparently have to trust to their habit of working under the covered ways which they construct, as well as to their activity and great numbers for their preservation.
I had thought that the very powerful, and, to me, disagreeable, odour of these little ants might have rendered them distasteful to the tiger-beetle, but this is evidently not the case.
I have said above that, as far as our present knowledge goes, only two out of the 104 species of European ants are possessed of the habit of collecting and storing seed, and it may be reasonably asked how it can have come about, if this is the case, that the ancient authors were so well acquainted with the fact.