Nov. 7, 1884.] 



♦ KNOWLEDGE • 



379 



out the differences between the two orders, Lepidoptera 

 (moths) and Trkhojitera (caddis-flies). 



On placing examples of each side by side, with wings 

 expanded, a superficial glance will detect little more 

 difference than that the wings of the caddis-fly, especially 

 the liind pair, have a semi-transparent and somewhat glossy 

 and iridescent appearance which is absent from those of the 

 moth, and the most important structural difl'erences will 

 need microscopic work for their complete determination. 

 Applying the microscope tirst to the wings, we find that in 

 the moth the pattern is due not to the colour of the wings 

 themselves, but to innumerable minute appendages in the 

 form of tiny scales attached to the wing by the pointed 

 end only, lapping over one another like slates on the roof of 

 a house, and producing by their different colours a sort of 

 mosaic pattern, the elements of which are so small that 

 the mosaic effect is lost when viewed simply by the 

 naked eye. On removing the scales, which can be done 

 by gently brushing with a camel's hair brush, we find that 

 the true wing consists of a transparent, colourless mem- 

 brane with nervures forming its framework. Examining 

 the caddis-fly in the same way, we see that the nervures 

 are more numerous, and that such pattern as there may be, 

 which is generally not a great deal, is produced partly by 

 the coloration of the membranous wing itself, and partly 

 by minute hairs, not scales, scattered more or less thickly 

 over the surface. These differences will generally suffice 

 for the separation of moths from caddis-flies ; but there are 

 a few moths that, so far as appearance and clothing of 

 wings are concerned, approach very near to the Trichop- 

 terous type, the wings being semi-transparent, glossy, and 

 iridescent, and the scales attenuated to such a degree as to 

 be scarcely distinguishable from hairs, a condition best 

 exemplified in the common pale brownish moth, Nudaria 

 mundana. The antennrc of a caddis-fly are generally pro- 

 portionately longer and stouter than those of a moth and 

 are carried, pointing straight forward in front of the 

 head. In the organs of the mouth (Fig. 1) there is a 



?>!-\ 



A B 



Fig. 1. — Side view of head of moth (A) and caddis-fly (B) ; a, 

 base of antenna^; ?y, labial palpi; m, maxiU;t;; my, maxiUarj- 

 palpi. 



great difference. The moth carries a pair of long, 

 flexible appendages closely applied to one another, and 

 curled up in a flat coU which is placed in a vertical 

 plane underneath the head ; no such coiled apparatus exists 

 in any other kinds of insects. On each side of this coil is 

 a jointed organ, clothed more or less thickly with scales, 

 the pair of which form between them a sort of groove, into 

 which the coil fits. These two pairs of organs are called 

 respectively maxillaj and labial palpi, and are the principal 

 organs of the mouth in the Lepidoptera. The maxilla^, which 

 can be ttncoiled at pleasure, carry along their inner edge, 

 which is grooved, numerous short hooks, those of one side 

 interlocking with those of the other, and thus forming a 

 central tube, up which the liquid food taken by the insect 

 must pass in order to enter the mouth, an aperture between 

 the bases of the maxillre. In the caddis-fly the only organs 

 distinctly perceptible are two pairs of delicate, jointed 



appendages, the maxillary and labial palpi. Though its 

 larva ])osses.sed a pair of stout jaws, and was able to make 

 good u.se of them, the perfect insect is, equally with the 

 moth, entire!}' destitute of any such organs : the moth's 

 coiled maxilla', however, sufliciently distinguish the insect. 

 In a few moths the maxillae are quite nidimentary, the 

 palpi being almost the only recognisable mouth organs : 

 this manifesth- approximates the mouth in ap]iearance to 

 the Trichopterous type, and there is a noteworthy instance 

 in which even competent entomologists were for a time 

 misled by this condition. The insect in question is a small, 

 whitish moth, called Acentropv.s niveus, which, as it is a 

 genuine lover of ponds, will come in for more lengthened 

 notice later on ; it was bandied about from one order to the 

 other, at one time being considered a caddis-fly, at another 

 a moth, till, the discussion having waxed hot and strong, 

 it found a final resting-place amongst the Lepidoptera. 



Some of the caddis-flies, viz., those of the family Lepto- 

 ceridcF, are remarkable for the enormous length of their 

 antennw, which are sometimes four or five times as long as 

 the body. It is these little creatures, some of them soot}- 

 black in colour, that form dancing groups just above the 

 surface of the water. By entomological beginners they are 

 sure to be mistaken for moths, especially as there is a 

 well-known family of moths of the same size, of similar 

 shape, with equally disproportionate antennfe, and with 

 their colours, too, sometimes not unlike those of the Lepto- 

 ceridie. Attention to the structural characteristics men- 

 tioned above will, however, infallibly lead the observer to 

 their true systematic position. It should constantly be 

 borne in mind that mere superficial resemblances count for 

 nothing to the systematist ; insects that look something 

 alike in general appearance are not necessarily at all related, 

 for there are numerous instances of mimicry between 

 species belonging to altogether different orders : an exami- 

 nation, therefore, which pays more attention to general 

 effect than to matters of detail, will often fail to detect 

 either real points of similarity or of disagreement ; and 

 students of entomology should be very careful in forming 

 an opinion as to an insect's systematic position without the 

 closest scrutiny of all essential parts, assisted by at least a 

 hand-lens, and, if necessary, even by the compound micro- 

 scope. 



Caddis-flies are to be found during the summer months. 

 Thev fly with a heavy, zigzag sort of flight, and when in 

 the net often simulate death, bringing the wings close along- 

 side the body (the hind pair, which are much larger than 

 the fore, being folded up Uke a fan), relaxing their hold, 

 and falling over on their side. But any attempt to secure 

 their persons will speedily convince them of the futility of 

 this pretence, and elicit spasmodic struggles for liberty. 



There are some other water-frequenting, winged crea- 

 tures, such as the stone-flies, willow-fly, and alder-fly, that, 

 like the caddises, are used as bait by anglers, and are there- 

 fore sometimes confounded with them. These, however, 

 though in habits resembling the subjects of the present 

 paper, are pretty easily seen, by examination of the wings, 

 not to belong to quite the same group ; their wings are 

 more or less closely reticulated by means of a number of 

 tra7isrerse nervures in addition to the longitudinal ones 

 (those of caddis-flies being chiefly longitudinal), and are 

 only reri/ slightly hairy, generally, indeed, imperceptibly so, 

 without considerable magnification ; and, in consequence, 

 are more transparent than those of caddis-flies. Most of 

 them, too, carry two long filaments at the tail, which the 

 true caddis-flies never do. These insects, together with a 

 number of others, such as May-flies, dragon-flies, snake-flies, 

 and lacewing-flies, constitute the wonderfully mixed assem- 

 blage known as the order Neuroptera — a group with which 



