Art. XXVIII.—Instances of Instinct in Insects.
[Read before the Wellington Philosophical Society, 9th September, 1891.]
The following remarks are offered as a supplement to Mr. Carlile's extremely interesting paper on “Animal Intelligence,” which I had the pleasure of hearing at one of our recent meetings. Two of the observations on instinctive habits are taken from recent numbers of the Entomologist's Monthly Magazine, while the other two are original.
In September, 1886, Mr. C. G. Barrett, F.E.S., recorded the following observation on the habits of a little black moth called Phycis carbonariella:—
“One of the most singular preferences known among small moths is that of Phycis carbonariella for burnt places on heaths. A fire, lighted by accident or for mischief, or sometimes to allow of the growth of young herbage, sweeps across a heath, destroying everything (plants and insects) for hundreds of yards, and leaves a dreary waste of burnt débris and charred sticks; and when the next autumn arrives Phycis carbonariella deserts the living heather, on which it surely must have fed, and resorts in numbers to this burnt ground. I have certainly seen a hundred specimens on such a piece of ground in less than an hour, when the whole number disturbed from among living heather in an afternoon would not exceed four or five, and this on occasions when they flew quite freely, towering in the wildest manner. The resemblance of the moth to the charred sticks is wonderfully close, and its sagacity in choosing such a resting-place would be equally surprising if it could only be satisfied to sit still, and not hurry away at the smallest alarm.
“The only satisfactory explanation appears to be that the creature has an acute-sense of the fitness of things, and, feeling that its black coat harmonizes but ill with anything that is living or growing, it congregates where the fire has reduced everything to the same carboniferous condition. This seems
to be an unexpected application (by the moth) of the theory of natural selection, but, as the normal condition of heaths can hardly be that of periodic burning, or can hardly have been so long enough to produce so important a modification in a moth, and as there are very few birds on these heaths, and none equal to inflicting serious damage on so active an insect, I can only suppose that a theory of individual preference is applicable in this case.—Chas. G. Barrett, King's Lynn, Norfolk, England. September, 1886.
In connection with this most interesting observation, I cannot help thinking that, even allowing for the scarcity of the birds, the habit of perching on burnt ground has probably been the result of natural selection. Prior to the burning of heaths no doubt the black coloration was useful to the insect for another purpose—possibly to absorb heat; but since the alteration in its environment has taken place the colouring has become serviceable for protective purposes. Hence it is probable that if adequate records had been kept we should find that the species had become much more numerous in recent times.
On the 5th October, 1890, while searching for insects on tree-trunks in the forest near Wellington, I heard an unusually loud buzzing sound in the neighbourhood. On endeavouring to ascertain the cause, I discovered a small hunting-spider of the grey species (family Salticidæ), which frequent sunny tree-trunks, struggling with a large flesh-fly fully four times its own size. The spider had seized its victim by the sternum, but the fly continued violently moving its legs and wings for more than eight minutes. During this time the little spider had considerable difficulty in detaining such a large insect.
In this case I think the action of the spider in biting its victim in the sternum, which is the seat of the great thoracic nerve-centre, and consequently the most vital part as regards locomotion, was undoubtedly instinctive. I do not imagine any one would contend that the spider had a knowledge of the internal anatomy of its victim, or that it acted through in-dividual experience. The obvious explanation is inherited instinct, or the experience of the race accumulated during countless generations by natural selection, preserving those individual spiders which were most successful in killing their prey.
On the 1st February of the present year I was collecting and observing insects in the same locality. Whilst approaching a mass of dead branches which was situated near the track I observed what appeared to be a leaf fall from one of the upper twigs, stop for a second on another twig, and finally come to rest on the ground amongst a lot of litter. I felt
perfectly sure it was a leaf, but was impelled for some reason to stoop down and look at it. On close examination I found it was a specimen of Drepanodes muriferata, a somewhat rare moth. The insect was resting with outspread wings, slightly turned upwards, and appeared exactly like a crumpled leaf on the ground. All the varieties of this species resemble dead leaves in their varied tints; but the insect's habit of falling like a leaf when disturbed is, of course, an instinctive action. I think in this case we have an example of structure and instinct developed simultaneously. It is evident that the instinct is just as independent of the will of the animal as its protective colouring, both having been essential to the species in avoiding destruction by insectivorous birds. It is also interesting to reflect on the immense number of abortive variations which must have occurred before the moth acquired its present habits and colouring.
The following notes on Osmia bicolor, Schk., are contributed by Mr. V. R. Perkins, F.E.S. (Entomologist's Monthly Magazine, July, 1891):—
“In vol. xxi., pp. 38 and 67, of this magazine I drew attention to what I considered was a very curious habit of Osmia bicolor, Schk., a habit, I believe, quite peculiar to this one bee—that of picking up dry bents of grass or stick and flying away with them in its mandibles. It is only the female that does this, and I concluded at the time I first noticed it that it must have something to do with nidifi-cation, but in what way I was at a loss to know. This bee is known to make use of the old shells of Helix nemoralis for its nidus. These it fills with its cells, and I have seen the bee right inside the whorl of this shell busily at work, and so captured it; but I have never seen any symptom of stick or bent connected with it; so it was a puzzle what the bees did with them. This present season, notwithstanding the very severe winter and continued cold spring, these bees were out and about quite as early and as numerously as usual, and by the middle of April they had become plentiful. I was too much engaged with other matters at that time to go and look after them, and it was on the 6th of this present month that I was able to get away to one of the spots where these bees can be watched attentively, and where I was not likely to be disturbed. I found the females in abundance, and they were at their old game; so now was my opportunity. I saw them alight on the ground, search about and select a bent, and then fly off with it. I was determined to solve the mystery if possible, so I crept about on my hands and knees, watching intently the bees flitting along the dry sunny bank, working in and out among the short herbage, and soon I saw one start up under my very nose, and I saw also a little pile of bents
collected into a heap, just such as the bees select. It struck me as a very peculiar-looking mound, and I took up the lot in my hand, when what should I see under it but a Helix shell full of cells of the Osmia! Here, then, was the explanation of the mystery plain enough. These bees, when they have filled a shell full of cells, set to work to cover it over—to hide it both from the sun's rays and from any birds, mice, insects, or other enemies that might chance to come across it. Having so far succeeded, I made up my mind to return the next morning, and prosecute my studies further in the same direction. I soon found another of these peculiar little constructions; so I sat myself down by it, and watched to see what would occur. I was close enough to take it up if I wanted to; but the bee came with her load, perfectly indifferent to my presence, and deposited it in her own peculiar way and to her own satisfaction, and then went away for another. She worked hard, and brought them rapidly one after another. With each one she would alight on the top of the mound, then look round, walk over it, and with her jaws push one of the ends into the heap where she wanted it to remain, and so fix it. As soon as she was satisfied with its position off she went for another, brought it in, and did exactly the same. Every bent was put in its proper place, and she never laid one simply down on the top while I watched her.
“These nests very much resemble those of Formica rufa in miniature; they are from 4in. to 6in. round the bottom, and are from 2in. to 3in. high, so that they are very easily detected when you once know what they are; and the labour spent upon them must be very great, for there are hundreds of bents in each, and each one is brought and added separately. I found some dozen or more, all within a short distance, and three so close together that I could watch the proceedings of them all at the same time. This furnishes a complete history of the habits of this wonderful little Osmia. —Wotton-under-Edge, England, 13th May, 1891.”
In this extremely interesting case, much as we might desire to attribute individual intelligence to the insect, I do not think it is possible to do so. The habits of the female bees, first in selecting the empty snail-shells as receptacles for their nests, and secondly in covering them over with sticks, have probably been gradually produced by an immense number of variations in instinct, those variations most favourable to the welfare of the young under the given conditions having been finally preserved. In the discussion which followed the reading of Mr. Carlile's paper, Mr. Harding contrasted instinct and reason, and showed how, in many respects, the former attribute was superior to the latter. If it is admitted that instinct is the inherited experience of the race, whilst reason
is that of the individual only, then the explanation of the superiority of instinct is obvious. Instinct is the result of continued selections from the experiences of countless generations, whilst reason is only the experience acquired during the brief lifetime of a single individual. It is not surprising, then, that instinct so vastly transcends the intellectual power of the animal that exhibits it. I think that we may look for the development of human instinct when most of our individual experience or knowledge has become hereditary. At present only the capacity for acquiring knowledge is inherited by human beings, but, judging from the facts above con-sidered, knowledge itself must in time be inherited also. So far from supposing, then, that we have lost our instincts through civilisation, I do not think that they have yet been evolved. Now nearly all our results have to be attained by long training and laborious mental calculations, but in the future we may hope to arrive at far greater results by almost unconscious instinctive processes.