INSECT MISCELLANIES.

SECTION I.

SENSES OF INSECTS.

It was well said by the distinguished Danish naturalist, Fabricius, that "nothing in natural history is more abstruse and difficult than an accurate description of the senses of animals*" This inherent complexity of the subject appears to have induced Lehmann to undertake the investigation of the senses of insects t. He collected into a focus all that was known previous to his time, though he has added very little from his own observation; but since that period much has been done by Marcel de Serres, Wollaston, Müller, and others.

The chief difficulty of the subject arises from the great physical differences which exist between animals furnished with bones and warm blood, and insects that have neither, rendering all inference from analogy much less to be depended on than if the physical structure of each were similar. When we see an elephant, for example, use his trunk to lift a small piece of money from the ground, we cannot doubt but that he feels the coin as plainly as we should do in lifting it with the hand, and hence the inference *Nye Samling as det Danske, &c. ii. 375.

† De Sensibus Externis Insectorum, p. 1, 4to., Gottinge, 1798,

B

that the trunk of the elephant is an organ of touch follows of course. But when we see an ichneumon fly vibrating its long antennæ before the entrance of a bee's nest, and sometimes even inserting one or both of them into the hole as if to explore its contents, we are not thence entitled to conclude that the antennæ are organs of touch, for they may, with as much probability, be inferred to be organs of hearing employed to listen to sounds produced by the inhabitant of the nest. It would also be too hasty, as it appears to us, to infer that flies, gnats, and moths, are endowed with eyes of very quick sight, because we find it difficult to approach them without putting them to flight; for the earth-worm (Lumbricus terrestris, LINN.) will retreat with similar rapidity into its hole when the light of a candle is thrown upon it at night, though no anatomist has ever discovered its eyes, nor believes that it has any; and the insects alluded to may be warned of the approach of danger by smell, by hearing, or by touch from slight changes in the currents of air, as probably as by sight. Analogy, it would thence appear, is very apt to mislead; and as we have little else to go upon in the subject of the senses in insects, we can seldom ascertain the facts with minute accuracy, and must rest contented with probabilities and approximations to the truth.

Respecting one point there can be no doubt,namely, that an object must always be present in order to produce a sensation or feeling; light and colours being in this manner the objects of the sense of seeing, and sound of the sense of hearing. In man the impression made by light upon the eye or by sound upon the ear passes along peculiar nerves to the brain, as the signal from a distant telegraph is communicated to a metropolis. In insects we may

* J. R.

suppose that such impressions upon the eye or the ear are only conveyed to the next nervous centre (ganglion), since they possess no general brain similar to ours, but a number of central points in different parts of the body where the adjacent nerves unite *. Whether, also, insects possess one set of nerves for feeling and another set for motion, as Mr. Charles Bell has recently discovered to be the case among larger animals, remains to be ascertained, though analogy would lead us to conclude that they must have something at least similar. Be this as it may, the most obvious mode in which we can discuss the subject before us, is to examine the structure of the organs, and the probable action of objects upon these. It appears to be the most convenient order to begin with the Sense of Touch, and then to take up Taste, Smell, Hearing, and Vision, in succession.

* See Insect Transformations, pp. 400 and 139.

CHAPTER I.

SENSE OF TOUCH.

THOUGH We may entertain considerable doubts of the accuracy of the poet's observation, when he says the spider

"Lives in each thread, and feels along the line,"

there can be no question that the legs of spiders possess considerable powers of touch, so far as resistance is concerned; for in constructing, and still more in repairing, their webs, they never advance a step without making sure of the strength of what has been already completed. They are not even always content with pulling the threads for this purpose, but frequently let themselves down like a plummet from the thread whose strength they wish to try, and bob backwards and forwards with the whole weight of the body. But that the acuteness with which the motion of the threads is felt, when a fly is caught in the net, chiefly governs the motions of the spider in seizing it, we doubt for several reasons. Spiders, for example, are furnished with not less than six, though more commonly with eight, eyes of sparkling brilliancy, and placed in a very prominent situation; and these we should be apt to look upon as in part superfluous, were the sense of touch so exquisite as is generally believed. We have tried numerous experiments by moving and vibrating the lines of the webs of many species, so as to imitate as nearly as possible the entrapment of a fly; but in no case have we

succeeded in bringing the spider to the spot, because, as we inferred, her eyes always detected our attempted deception. But when a fly is held near a web and made to buz, the spider in most cases will peep from her lurking-hole, to look whether it has not been caught in some of the lines or meshes not under her view, proving that the sense of hearing is as acute and useful in such cases as either vision or touch. It appears, further, that a small spider ascertains by touch the superior strength of a blow-fly or a large syrphus which may chance to be caught in its web, hesitating long before venturing to attack it, and sometimes never venturing at all,-a circumstance we have often remarked, and we have frequently, besides, repeated the experiment of putting large flies in the webs of small spiders with similar results *.

The stretching out of the legs of the long-bodied spider (Tetragnatha extensa, LATR.), when it places itself in the centre of its geometric web, appears to have given origin to the opinion under review: though it may be remarked that it does not spread its legs around so as to take cognizance of as many lines as possible, but, on the contrary, huddles them into a close bundle, more apparently with the view of making them appear motionless and lifeless than actively on the alert. This view is still more strongly proved by the circumstance, that when this spider is not on its web watching for prey, but resting on a wall, or in the fold of a leaf, it stretches out its legs in the

same manner.

The long-legged house spider (Pholcus phalangioides, WALCK.) may be referred to as giving more countenance to the opinion, because it not only spins a very loose irregular web in the corners of walls, but keeps its legs spread about as if on purpose to feel the more readily when any thing is caught. We

*J. R.