The Senses of Insects.

Otago Witness, Issue 2849, 21 October 1908, Page 76

The Senses of Insects.

Dtr Auguste Foi«l'« important work. "The Senses of Insects?" (Aicthu-en and Co.). has obtained very ooiibid-craLlo attention on the Continent. Tins fascinating book, translated by Mr MacLeod Yoai^lcy, { and dedicated to lx>rd A-v-ebuiy, whose ! patient researches have dune so much to ; stimulate interest in tho myriads of mys- ■ terious in.-aeets arotuid us, will oj.en up to ' the unscientific a field of observation pos1 sibly undreamed of, and, in tho author's I words, "teach them, to look with a mor-e i kindly eye upon tho£>e being.s' 1 * whoto doings hitherto lia\e perhaps only annojed them. It is a world oi marvels, to which Dr Forol dntroduoed such readers. In his chapters on vision he points out that it can be proved that insects are especially able to perceive motion. "There are only a very few insects that can see distinctly. For example, I watched one day a wasp chasing a fly on the wall of a verandah, as is the habit of this in- ! sect at the end of summer and in the ! auttunn. She dashed violently in flight 1 at the flies sitting on the wall, which I mostly escaped. j ''She continued her pursuit with remark- ' able pertinacity, and buceeeded on several 1 occasions in, catching a, fly, which she 1 .killed, mutilated, and bore away to her ' nest. Each time she quickly returned to ' continue tho hunt. In one spot of the 1 wall • was stuck a- • black naii, which wae ' just the size of a fly, and I saw the wasp . very frequently deceived by this nail, upon ' which she sprang, leaving it as ooon as she perceived her error on touching it. Nevertheless, she made the same mistake with thf nail fehortly aft^r. "I have often made similar observations. We may cc-rtuinh conclude that the wasg faw something rho eizc of a fly, but without <i I=l.l ntriH>-hjng th<* detail*:; therefore, she tew it indistinctly. 10\ iiiently the waM) nor only perceived motio'i; .-he also distinguit-lKd tho- eizc of objects '*J, "Wh<*n I put d<-.id iiio on n, table to be ] carried off by another wasp, she took them, one after the other, a* veil <-pideis and

' insects of but little different size placed by their side. On the other ' hand, she took no notice of- insects much larger or , much smaller put among the flies. The J last exoerimant is >a very easy one to try, for the deception of wasps by giving them { { inert objects of the size and colour of < flies. "Many entomologists have observed- with what ingenuity and sureness dragon-flies distinguish, follow, and catch the smallest j insects on jthe wmg. Of all insects, tihey have, beyond compare, the best sight. ■ j Their enormous convex eyes have the • greatest number of facets, equalled only j by the eyes of the diurnal lepidoptera. ' Their number has been estimated at 12,000, | 17,000, etc. — The Hunter and the Dragon-fly. — "Their aerial chases resemble those of ' the swallows. By trying to catch them j , at the edge of a large pond, one can easily ' j convince oneself that dragon-flies amuse ! j themselves by making sport of the hunter; j J they will always allow one to approach. I just neai enough to- mise catching them (I speak of iEschna, Goniphus, and Libellula). "It can be seen to what degree they are able to measure the distance and reach of < j their enemy. It is an absolute fact that . ' dragon-flies (unless it is cold or in the • evening) always manage to fly at just that ; distance at which the entomologist cannot ' touch them, and they see perfectly well , [ whether one is ■armed with a net or has ■ nothing _ but his hands; one might even ' say that jthey measure the length of the handle of the net, for the ..possession, of a I long handle is no advantage. They fly , ■j just out of reach of one's instrument, what- i ! ever trouble one maf give oneself by ' hiding it from them and suddenly lunging ! as they fly off. v._ ( "It- i© known that many insects will i blindly fly and dash against a lamp at^ night until they burn themselves. It has ■ often been wrongly thought that they were fascinated. We ought to remember that natural lights, concentrated at one point like our artificial lights, are extremely rare in . Nature. j "The light of day, which is the light i of wild animals, is not concentrated at one ' point. Ineecte when they are in darkness j (underground, beneath bark or leaves) are j accustomed to reach the open air, where the light is everywhere diffused, by directing themselves towards the luminous point. "At night, when they fly towards a lamp, they- ore evidently deceived, and their small brains cannot comprehend the novelty of this light concentrated at one spot. Consequently their fruitless efforts , aro again and again renewed against the flame, and the poor innocents end by burn- j ing themselves. i "Several domestic insects 1 , which have evidently- become little by little adapted to artificial light in the course of generations, I no longer allow- themselves to be deceived , thereby. This is the ease with houseflies. { "T© what extent do insects perceive i form — that ia to 6ay, the dimensions and ' contours of whatever catches their eye? , It is very evident that they do not perceive ■ it as dearly as we do, but it seems to me undoubted that, when they possess welldeveloped compound eyes, they appreciate • size, and more or less distinctly the con- j tours of objects. j "How could they otherwise measure distances, alight from, the wing on to objects with so much precision, orient themselves so well (find again with certainty-such and' • such a stone, some particular corner of , ground, some special bit of wood), despite , the absence of the sense of smell? The : following^ •experiment, conducted after Lub- j bock's method, seems to me to show that i wasps and bumble bees distinguished tihe , shape of objects, as ie, further, the opinion ' of X^ul>boc]c aJso—The White-paper Experiment. — "I placed a wasp (V. germanica) on some honey put on a disc of white paper a little more than thocee centimetres in diameter, the whole being put on my trunk. After gorging the honey the wasp flew off, and soon returned straight to the white paper, where she gorged herself a second time with the honey. "I then replaced the disc of white paper by a similar disc (with the honey) at t'hc side, about two inches away. The wasp, returning, went frrst to the empty disc (in ■ the old place) ; then, finding nothing on '< it, raised herself a little in the air, hovered , two or throe times, saw tho other di.«c, j went for it, and gorged herself anew with i honey. j "I profited by her fr^ali absence to put ' I the honey this time on a cross of white ' paper 11^ centimetres long, in all directions, and with branches 2j centimetres ' broad. •'The cross and the <Ji«c without honey 1 were pJaced close to one anothrr on each fijde of the place to wluch ilio wa-p came 1 for her lepast. When tho wa?p returned ehe searched a little uu<\ found the h-oii-ey ! very quickly. I thought th<> cross diffeied . I too little from the cli»c, an<l I cut out some ' band« of paper 10 centimetre* long and ! 8 millimetres broad. ! I "After the departure of the wa«»p I re- i 1 moved the cross and placed on eaeli side j ! of the place where it had been, at about , ' ' tho same distance from the latter (one or , i two inches), on one side, a white disc with- , j out honey. As soon as the wasp returned j J 6he flew straight to the white diec, where j she vainly searched for the honey a long , time. i "Then ehe searched tho middle, on the ! grey bottom of the trunk where the honey j j had been, and finding nothing flew away* | j But ahe returned quickly, searched anew > ]on tho disc, then on the old grey place ; » . • then she began to smell and hunt about to > ' j right and left so well that she ended by finding the honey. j ' "It was interesting to 6ee the same wasp (she brought no companions) remember the , paper on each occasion at which she had j eaten on tho last- of her visits, and judge j of it by its shape and size, for I replaced the honey paper every time by another paper cut on the same model." j ' Spiders appear to see very badly. "Web- j spinning spiders recog-ni=e their prey by ' tho vibration of the web, by means of , ' touch. A little attentive observations will ( : ' convince one of this. | ' "As to jumping spiders, it appears to : , me that they only see their prey when they | move at a short distance from them. Then they turn in their direction and spring ' ' upon them." ' ! Regarding- the memory of inse-cts, Dr | Forel t-a> - : "I lune observed that wasps ' have a much better memory of places than ' ', humble-bees, although the sight of tho I latter is rather better, acd we have seen

that this memory is independent of the antennae.." —The Memory of Insects. — j "The males of ants show scarcely any . trace of memory, and this is the case with . many solitary insects, but not with all. Thus a Dytisous" marginalis that 1 had in a bowl, and which I was in the habit of feeding when I returned., finally became ' somewhat -tame. Instead- of flying' to the ' bottom of the bowl - when I entered, as he did at the beginning, he started to jump J almost out of the water, and immediately i seized what I gave him, even the end--of my fingers. ""Heretofore tranquil, he began to move when he saw me come in. He must h*Tpe j remembered that it was I who brought ', him food (I do not- believe he. distinguished i me from another person). I even got to making thi6 aquatic insect eat on my table. Only he instinctively acted as in the -water, and" stretched his front feet forward, which , made him tumble regularly on his back, ' but did not prevent him from finishing his ' repast in this abnormal position."