Apkil 1, 1869.3 



rlARDWICKE'S SCIENCE-GOSSIP. 



77 



through them, that the ladies of the family who 

 resided there at the time avoided them in their 

 evening walks. It is not unlikely that these 

 annelides may prove to have been all this time 

 under the eyes of zoologists in their own head- 

 quarters, for Mr. Bartlett tells me that he has often 

 seen leeches on the greensward in the Regent's 

 Park Gardens. "Whether they are Trocheta or of 

 some other genus, remains of course to be seen. I 

 request the attention of our correspondents to the 

 concluding paragraph of Dr. Baird's letter. Any 

 British leeches, large or small, will be received with 

 thanks by Mr. Buckland or myself for the autho- 

 rities of the British Museum and for our own 

 examination.— Land and Water, March 13, 1869. 



Henky Lee. 



INFLUENCE OE LIGHT ON INSECTS. 



T IGHT, though not actually necessary to the 

 -" maintenance of insect life, has nevertheless so 

 strong a bearing on it, that the proportion.of insects 

 existing without it is infinitesimally small. Among 

 them are certain Coleoptera, found in the monster 

 caves of Carinthia, which pass their whole existence 

 in total darkness, and which are without any organs 

 of vision. Indeed, wherever insects are compelled 

 to go through life without coming in contact with 

 the sun's rays, the eyes are sure to be either 

 obsolete, or so imperfect as to be practically useless : 

 such is the case with Claviger testacevs, Preyss, 

 which lives under stones in ants' nests : and also 

 with Sphodms leucophthalmus, L., Tridonychus 

 terricola, 111., and a few other species, when bred in 

 cellars or similar places, where the light never 

 penetrates. Numbers of insects, which see 

 perfectly well, prefer to remain in retirement during 

 the day, and only issue forth when the sun has sunk 

 into the west. Most of us know to our cost, how 

 active the gnats become in the summer's evening : 

 and many too have listened to the "drowsy hum" 

 of the dor beetle, or watched the "mazy dance " of 

 the May fly: still later the glowworm lights her 

 lamp, a signal to whole hosts of moths and beetles 

 to come forth and seek their mates, or search for 

 prey ; not to mention the crickets, cockroaches, 

 earwigs, bugs, lepisma, &c., all of which, like guilty 

 things, hurry back to their retreats with the first 

 blush of dawn. Most of the night-loving insects are 

 so affected by the sudden appearance of light, that 

 when a candle is introduced, they rush madly into 

 the flame, as though they were deliberately anxious 

 to commit suicide. " The moth circling round the 

 flame " has many a time and oft served " to point a 

 moral and adorn a tale." The true cause of this 

 eccentric proceeding has never yet been satisfac- 

 torily explained. It has been suggested that their 

 eyes do not absorb (as in most insects), but reflect 

 the light : an organisation which enables them to 



distinguish objects in a state of partial darkness, 

 but which leads to their destruction when the light 

 is strong. Blinded, as it were, by excess of radiance, 

 they lose all discernment in the blaze, and perish in 

 the flame. 



The larvae as a rule seek their food only in the day 

 time : still there are some night feeders, to whom 

 the light is distasteful, if not hurtful : as for 

 instance, the caterpillar of the shark moth (Cuciillia 

 umbratica (L.), the buff arches {Thyatira derasa, L.), 

 and the heart and dart moth [Agrotis exclamationis, 

 W. V.). 



It is, however, in the colouring of the outer 

 integument, that the potent agency of the solar ray 

 is shown most conspicuously. Speaking generally, 

 the stronger the light, the more intense and brilliant 

 is the hue, and the more delicate is the play of 

 colour. Such larva; as are produced below the soil 

 or in shady spots, to which the light of day has little 

 access, are constantly white and colourless ; and 

 this bleached appearance clings to the perfect insect 

 so long as the conditions remain the same. Leunis, 

 in his "Thierreich," tells us, "that he accidentally left 

 a bug {Acantlria ledularia, L.) shut up in a box for 

 no less than six months : on again opening the box, 

 he found the animal alive and surrounded by young 

 ones, all of which, together with the mother, were 

 quite white, and ' transparent as glass.' " 



On the other hand, insects, which pass their lives 

 " from the cradle to the grave " in broad daylight 

 (as for example butterflies and chrysomelids), are 

 far more gaily tinted, than the nightflying moths 

 and Coleoptera, which have never been exposed to 

 the solar rays. 



The influence of light, as might be expected, 

 shows itself very remarkably in regard to the 

 geographical zones : the insects of the tropics being, 

 as a rule, far more elegantly and brilliantly coloured 

 than those which are confined to the temperate and 

 arctic regions. 



On looking over a well stocked museum, a very 

 fair guess may be made, at a single glance, as to the 

 quarter of the globe to which we may assign many 

 of the Lepidoptera, the Nymphalids, the Morphos, 

 the Uranias, by the side of which our peacocks j 

 emperors, and admirals look dingy and homely to a 

 degree. What a striking contrast is presented in 

 the two nearly related beetles, Entimus imperialis, 

 Eabr., the gorgeous diamond weevil of Brazil, and 

 our common hedge weevil (Polydrosus micans,Germ.). 

 Nature seems to revel in the glorious ornamentation 

 which she has scattered without stint over the 

 brilliant Entimus, whose wing-covers especially are 

 encrusted with scales, which rival the noblest 

 precious stones in the exquisite play of light 

 reflected from every part of their surface, and which 

 are still further set off by being embedded in hollows 

 on a jet black background, of a velvety lustre. 

 Nor are Nature's lavish gifts confined to this single 



