December 1, 1898.] 



KNOWLEDGE. 



227 



Coleoptera, or beetles. Many of these insects feed upon 

 plants, and amongst these vegetarian groups arc several 

 species that construct cocoons. Two of the most interesting 

 instances may be mentioned, both taken from the beetles 

 called weevils. A w'eevil may be easily recognized by the 

 peculiar structure of its face ; this is prolonged into a longer 

 or shorter beak or snout, sometimes reminding one of an 

 elephant's trunk, and carrying the mouth organs at the 

 tip. Hi/prra vdriabilis is the name given to a brownish 

 species which feeds upon various leguminous plants, and, 

 while generally common, is sometimes found in absolute 

 profusion. The grub of this creature, a short caterpillar- 

 like being, covers its body with a sticky substance secreted 

 by a gland placed at the tail. When it has eaten its 

 destined amount of lucerne or other leguminous food, and 

 reached its full size, it retires to the underside of a leaf, 

 and begins to construct there, with this same sticky 

 substance, a kind of oval cage consisting of a thin and 

 open network of threads. Within this the little creature 

 enters upon its pupal experience, remaining, of course, still 

 visible from the outside through the meshes of the network. 

 Few natural objects are more graceful and delicate than 

 these little cages, which may often be seen attached to 

 leaves. The construction of the cage is rather a slow 

 business, occupying, although it is not a large structure 

 and the network is but one layer thick, about twenty-four 

 hours in completion. So delicate a structure would, no 

 doubt, stand but little wear and tear, and would be a most 

 imperfect shelter against climatic changes ; but fortunately 

 its durability is not greatly put to the test, for the perfect 

 beetle is rapidly developed within, and issues after only a 

 few days of captivity. The genus Ht/pcra is a large one, 

 containing sixteen British species, the habits of all of 

 which are similar to those detailed above. 



The other instance of beetle cocoons is that of the genus 

 Clonus. Here we have half a dozen species of extremely 

 pretty weevils, with large globular bodies, variously 

 coloured, and always adorned with raised velvety patches, 

 some of which are rectangular streaks and others circular 

 discs. These beetles are specially attached to one order 

 of plants, the Scrophuhriacea, and particularly to those 

 members of it called fig worts (Scrophularia). The fig worts 

 grow in damp places m tall clusters ; they may be known 

 by their disagreeable odour, their succulent stems carrying 

 opposite pairs of smooth, broad, rounded leaves with 

 notched edges, and their bunches of small, deep red, cup- 

 shaped flowers at the top. The flowers do not all open at 

 the same time, so that often there may be seen on the 

 same cluster buds, flowers, and seed-vessels. Sometimes 

 the leaves of these plants are seen to be riddled with holes, 

 as though someone had been making them a target for the 

 discharge of small shot ; the leaves are then more or less 

 di'y and brown. This damage is wi'ought by the larvre of 

 weevils belonging to the genus Ciomis, and a little close 

 inspection will usually reveal the beetles crouching down 

 on the leaves ; or failing this, if the eye be carried to the 

 bunch of flowers, buds, and seed-vessels at the top of 

 the stem, a still more careful scrutiny will probably detect 

 a number of oval olive-brown bodies amongst the rounded 

 buds and seed-vessels, and very closely resembling them 

 in appearance (Fig. 7). These are the cocoons of the 

 beetles, and though perfectly exposed, they are yet beau- 

 tifully concealed by their resemblance to the fruitage of 

 the plant. In many respects the economy of these insects 

 is like that of the genus llypera : there is the same sticky 

 secretion on the larvie, furnished by a gland at the tail, 

 and as before it is worked up into an oval cocoon to enclose 

 the pupa. But there is this difference : whereas the cocoon of 

 Uypera is a network, that of Clonus is a continuous papery 



Fig. 7. — Part of Fignort Flower-head, 

 with seed-vessels and cocoons of 

 Ciontis scrophiilarut. 



layer without openings, so that the chrysalis is entirely 

 hidden. The structure, in fact, reminds one of a child's 

 air ball, and within it the chrysalis lies free, rattling 

 against the sides when shaken. Within its balloon-like 



covering the insect lies 

 for about a week, when 

 it casts its last skin, 

 cuts nearly off a neat 

 segment from the bot- 

 tom of the cocoon, 

 and crawls out through 

 the hole. From the 

 above it will be seen 

 that these beetle co- 

 coons are not strictly 

 comparable with those 

 of moths, inasmuch as 

 the material of which 

 they are composed is 

 secreted, not by a 

 gland opening beneath the mouth, but by one which 

 opens upon the upper surface of the last segment of the 

 body. 



A third order of insects, the Hymenoptera, now claims 

 our attention, for the habit of cocoon-forming is widely 

 extended, and occurs amongst most of the groups of 

 insects whose metamorphosis is complete. Our illustra- 

 tions will be taken from the parasitic members of this 

 extensive order, which go by the general name of ichneumon 

 flies. They are long-legged, thin-bodied, four-winged 

 insects, with long antennie and very often with the body 

 terminating in a longer or shorter stick-like ovipositor. 

 Most of them are daring their larvahood internal parasites 

 of other insects, their footless maggots living inside the 

 bodies of caterpillars and other larva3, and subsisting at 

 the expense of the tissues of their hosts, whose ruin they 

 thus achieve. Of these creatures, two extensive and well- 

 defined families are recognized — the Ichneumonidce and the 

 Braronidce. These two groups are very similar in general 

 appearance, and certain members of the one family closely 

 mimic certain of the other, so that a novice who did not 

 know exactly what points to look for in endeavouring to 

 distinguish them, would probably consider as identical two 

 insects that would be in reality widely different, as would 

 at once become evident if their whole life-histories could be 

 simultaneously passed in review. But they may very 

 easily be distinguished by paying attention to the arrange- 

 ment of the nervures of the fore-wings. A comparison of 

 the two wings in Fig. 8 will at once make this plain. In 

 both there is a dark spot, 

 called the " stigma," 

 more than half-way 

 along the upper margin 

 of the wing ; in the 

 lohneumonid the space 

 immediately beneath 

 this forms a large cell of 

 a more or less distinctly 

 five-sided outline and 

 with its lower and outer 

 edge concave ; in the 

 Braconid the same 

 space is occupied by 

 three cells, each roughly 

 four-sided. The little 

 nervure marked n also 



is present in the one and absent in the other. There is 

 endless diversity in the actual forms of these cells in the 

 different genera, but the general plan remains much the 



Fia. 8.- 



-Fore 

 Qonid, 



wings of (a) Ichueu- 

 (b) Braconid. 



