498 



• KNOWLEDGE • 



[Dec. I'J, 1884. 



elegantly adorned with a delicate tracery of brown or 

 black on a satiny white or creamy ground. Like most of 

 the Pyrales — the section to which they belong — they liave 

 long slender legs and a narrow body, extending considerably 

 beyond the hind wings. To find these beautiful little 

 beings, seek out a jiond where tall plants, such as the Burr- 

 reed, the Arrow-head, the Flowering Rush, and the Water 

 Plantain rise in stately columns straight out of the water, 

 and where the water itself is well stocked with pond- weeds; 

 watch the luxuriant growth for a time, and you will see at 

 any rate some of the Hydroeampidaj playing "hide-and- 

 seek," as it were, amongst the forest of stalks and leaves. 

 Some of their delicate forms are sure to be seen floating on 

 the water in a more or less disintegrated condition — the 

 corpses of such as have either been accidentally drowned, 

 or have perished in the ordinary course of nature, and 

 fallen into the water on their decease. Good specimens of 

 the living insects may easily be secured by sweeping 

 amongst their hiding-places, or by netting them as they 

 dart out from amongst the herbage. 



When at rest, the fore-wings are placed nearly horizon- 

 tally, just covering tlic liind wings, aud giving the whole 

 insect an outline resembling that of an isosceles triangle. 

 The attitude of rest is a matter of importance to the 

 systematic Lepidopterist, for often special attitudes are 

 characteristic of special families. Thus we find that some 

 moths spread out all four wings horizontally, closely 

 applying them to the object on which they are resting ; 

 some turn them up over their back, as butterflies do ; others 

 wrap them alongside the body so as to give themselves a 

 cylindrical appearance ; some rest with head close to the 

 ground and tail in the air, others in just the reverse posi- 

 tion, while, as regards the slope of the wings, there is every 

 cjnceivable degree of inclination between horizontal and 

 perpendicular, and, as a consequence, an infinite variety 

 of triangular outline. But, to return to our China 

 Marks. The prettiest of the family is Hydrocampa 

 stagnalis, the "Beautiful China Mark" (Fig. 1). The 



Fig. 1. — Hydrocampa stagnalis. 



ground colour of the wings is satiny-white, and the 

 markings consist of double, twisted lines of a rich brown 

 colour. Beautiful to the naked eye, it is simply exquisite 

 when viewed by reflected light with a low power of the 

 compound microscope ; the satiny scales lying row upon 

 row on the wings, and standing erect on the head like regal 

 plumes, glisten with dazzling brightness, tempered only 

 by the warm brown tints of the wavy lines that form the 

 pattern. Sloping back at the sides of the thorax, and con- 

 cealing the junction of wings with body, are two plume- 

 covered tippets, found in all Lepidoptera, but of unusually 

 large proportions in this group. The antenna} are most 

 elegant. To the naked eye, they are but fine threads; 

 but under the microscope (Fig. 2) each is seen to be 



rig. 2. — Ponion of antenna of Hydrocampa stagnalis, highly 

 magnified. 



composed of a series of joints carrying on their outer side 

 a little tuft of scales similar to those on the win?, and on 



the inner side a number of fine thort hairs standing erect 

 like velvet pile. 



But it is not in their perfect state that the principal 

 interest attaches to the Hydrocampid;e ; they are re- 

 markable as being the only family of the Lepidoptera that 

 are aquatic in the larval condition. Their caterpillars feed 

 on water-plants and form cases, not like caddis-worms, of 

 ve;;etable debris, but of the fresh leaves of the plants on 

 which they feed, and within these they constantly remain 

 beneath the surface of the water. That a caterpillar should 

 construct a case for itself out of the leaves of its food-plant 

 is nothing extraordinary, there being numerous instances of 

 it amongst the Lepidoptera ; indeed, one large family of 

 minute moth.«, the Coleophorida;, or "case-bearers," have 

 been so named from their indulgence in this habit ; but 

 tint a Lepidopterous caterpillar should habitually live in 

 water is an altogether anomalous fact, as submergence i.s 

 generally very fatal to these insects. Like those of the Lepi- 

 doptera generally, these caterpillars are worm-like beings, 

 with a hard head armed with powerful jaws, and with six 

 short legs in front, and claspers, or false legs, on the hinder 

 segments. The eggs are laid on the leaves of pond-weeds, 

 and in some cases, at any rate, the young grubs, when first 

 hatched, instead of at once making cases, mine their way 

 into the substance of the plant, and thus protect themselves 

 while devouring its interior. The duration of this internal 

 life seems to vary with the season ; those that are hatched 

 late in the year remain in their burrows all through 

 the winter aud do not form cases till the next spring, 

 when the freshly-growing plants afibrd them suitable 

 materials. But others have been observed to mine for only 

 a few days, and then to emerge and begin to construct 

 cases. The case is made of two pieces of leaf joined at the 

 edges. In order to construct it the caterpillar, by means 

 of its claspers, first seizes a leaf firmly near its edge, and 

 then bites a narrow, curved channel through the leaf, 

 beginning at the edge, and working its way round by bend- 

 ing its head to one side. Having then gone over the same 

 ground again, but in the reverse direction, widening the 

 channel, it shifts its claspers to the fixed part of the leaf, 

 and continues the curve almost to the edge again, repeating 

 this operation also a second time. The strip of leaf is now 

 attached only by a narrow isthmus. The caterpillar next 

 transfers itself to this almost detached portion, severs the 

 connecting bridge, and floats away as on a raft. In this 

 way half the case is made ; then, seizing some fixed leaf in 

 its forelegs, and guiding itself thereby, it crawls about in 

 f earch of a suitable leaf from which to cut a piece for the 

 other half. Having found one to its taste, it hauls itself 

 and raft under the chosen leaf and makes the detached 

 piece fast to the underside by fixing it with silk at intervals 

 along the edge, all the time keeping itself snugly ensconced 

 between the two. Having thus laid the foundation, as it 

 were, it uses the lower piece as a tracing model, cuts out 

 the upper by biting round the edges of the lower, and thus 

 finishes the dwelling, no doubt satisfied enough with the 

 economy of its arrangements, which have combined in the 

 most pleasurable way the taking of a meal and the building 

 of a domicile. 



From the open end of this case it can easily feed on the 

 plants around without unduly exposing its defenceless 

 body. But even the best-made cases will grow old, and 

 caterpillars, too, will grow stout, so that there is constant 

 need for the manifestation of constructive genius. The 

 larva^ are by no means fastidious as to the kind of leaf 

 used for the case, and sometimes the two halves even will 

 be of diflTerent materials. Sometimes only half the case is 

 changed at a time, a new roof or floor being put on as 

 occasion may require ; but care is always taken that the 



