314 



NATURE 



\_Atigust 5, 1880 



not only neglect rebcarch, but even their students in the 

 most unblushing manner, in their greed of gold. We hope 

 that when next Mr. Mundella has to ask for a vote for the 

 Science and Art Department, he will present as strong a 

 case for the encouragement of advanced science as he 

 has done for the teaching of elementary science. The 

 facts and figures in favour of the one are as strong as 

 those in favour of the other. 



EUROPEAN CADDIS-FLIES 



A Monographic Revision and Synopsis of the Trichoptcra 

 of the European Fauna. By Robert McLachlan, 

 F.R.S., F.L.S., &c. (London : \'an Voorst, 1S74- 

 1880.) 



MOST persons have seen those curious aquatic insects 

 called caddis-worms, which live at the bottom of 

 the water, protected by tubular cases formed of bits of 

 stick, stones, sand, or shells, and are much used as bait 

 by anglers ; being, as Izaak Walton remarked, " a choice 

 bait for the chub or chavender, or indeed for any great 

 fish." It is also generally known that these caddis-worms 

 are the larva: or grubs of winged insects, known as caddis- 

 flies or water-moths, which abound in the vicinity of 

 rivers or ponds and often fly into houses attracted by the 

 light ; but few persons except entomologists are aware that 

 there are nearly a hundred and fifty ditterent species in 

 the British Isles, while between four and five hundred are 

 known from various parts of Europe — that they constitute 

 a distinct order of insects, named " Trichoptera," from 

 their hairy wings — and that they possess peculiarities of 

 structure of the greatest interest as serving to connect, 

 however imperfectly, such distinct and highly speciaUsed 

 orders, as the Hymenoptera and the Lepidoptera. 



The perfect insects are characterised by four ample 

 membranous wings, of which the hind pair are usually 

 the largest, while the front pair are somewhat more 

 leathery in texture. The wings are always more or less 

 clothed with hair, sometimes to such an extent as to form 

 a dense coat which completely hides the nervures ; and it 

 is this peculiar hairy covering which has given the name 

 to the family. The neuration of the wings consists of 

 longitudinal branching veins with a few cross veins 

 forming cells, very different from the netted veins of 

 most of the Neuroptera, with which the Trichoptera 

 were formerly united, but bearing a considerable re- 

 semblance to those of some of the smaller moths. The 

 body is also hairy, the legs long and spined, while the 

 antennas are usually longer than the body, slender and 

 thread-like ; and when the insect is in repose these are 

 directed forward, and so closely pressed together as to 

 appear like one. The mouth is very small with quite 

 rudimentary mandibles, and M)-. McLachlan thinks that 

 the insects usually take no nutriment whatever in the 

 perfect state, "existing on the superabundant vitality 

 acquired during their long larval stage," but he adds: 

 "some of the larger species frequent flowers at night 

 after the manner of moths, and are even attracted by the 

 mixtures used by lepidopterists to attract their favourite 

 insects, facts which prove that some, at any rate, partake 

 of liquid nutriment." The exact mode in which this is 

 effected is not yet clearly ascertained. 



The eggs are gelatinous, and stick together in a mass 

 which is attached to aquatic plants below the surface of 

 the water, into which the female is said sometimes to 

 enter for the purpose of depositing them in a proper situa- 

 tion. The cases formed by the larvae are built up of 

 various substances fastened together by silken threads 

 spun from the mouth in the same manner as caterpillars 

 spin their cocoons — another curious point of resemblance to 

 the Lepidoptera. These cases vary greatly in the different 

 families and genera, and though at present very imper- 

 fectly known it seems probable that every species has a 

 distinctive form of case. The Phryganeidce, for example 

 make cylindrical cases of morsels of leaves or fibres 

 arranged in a spiral manner, the cases are open at both 

 ends, and it is believed that the larvK have the power of 

 turning in them. When about to change into a pupa the 

 larva closes up the ends with vegetable matter and 

 attaches the case to an aquatic plant. They live only in 

 ponds, lakes, or marshes. Another family — the Limno- 

 philidje — have some genera which live in still, others in 

 running waters, and their cases vary greatly, the most 

 curious being those formed entirely of shells, often taken 

 while their inmates are alive. One genus of this family — 

 Enoicycia — is altogether anomalous, since the female has 

 rudimentary wings and its larva lives in moss, often in 

 woods far away from water, forming a case of fine sand 

 intermixed with vegetable matter. One species is found 

 in England. In the next family — Sericostomatids — the 

 larva; live generally in streams, forming cylindrical cases 

 of sand or small stones, but sometimes the cases are 

 broad and flattened, in others quadrangular, while in one 

 genus — Helicopsyche — they are spiral, formed of sand 

 grains, and often so closely resembling the shells of fresh- 

 water molluscs, that some of them have been described 

 as species of Valvata, Paludina, &c. ! In the Hydro- 

 psychida; and Rhyacophilidos the larvre are carnivorous) 

 and form irregular cases of small stones fixed to larger 

 stones at the bottom of the water, and sometimes several 

 larvK appear to live in company under a common covering 

 of vegetable and other dchi is fastened together with silk. 

 These are obliged to quit their retreats when wandering 

 about in search of food, and they accordingly have the 

 body and abdomen of a firmer consistency. The Rhyaco- 

 philida; especially frequent torrents. Lastly, the Hydro- 

 philida; live in more or less seed-like, movable cases, 

 formed of silk with minute sand-grains, and having a slit 

 at each end forming two apertures, from either of which 

 the larva can protrude its head. They are found among 

 water-plants, on the surface of stones at the bottom of 

 streams or ponds, and have the power of spinning a 

 silken thread by which both the case and its inhabitant 

 can float securely in the water. The insects produced 

 from these larva are the smallest of the order, and often 

 appear in great numbers. 



When the larvae of Trichoptera are about to change 

 into pup;i; they close up the apertures of their cases either 

 with a network of threads or with other materials, and 

 some of them besides spi'^ an inner cocoon. The pupa;, 

 though quite motionless, bear a considerable resemblance 

 to the perfect insect, the antennx, legs, and wings being 

 fully formed, but shorter, and all inclosed in separate 

 sheaths and arranged on the breast. The head is how- 

 ever armed with a pair of strong horny hooks or jaws 



