24 



* KNOWLEDGE 



[Jlly 11, 1884. 



faith. That they have coiue to be mistaken for the ideas 

 symbolised; that with the lofiiest spiritual teaching there 

 should remain commingled belief in miraculous power in 

 fragments (mostly spurioue) of dead men and their clothes ; 

 only shows the persistency of that notion of a vital connec- 

 tion between the lifeless and the living which this jiaper 

 has sought to illustrate. 



THE ENTOMOLOGY OF A POND. 



By E. a. Butler. 



THE MIDDLK DEPTHS {continited). 



THE larvw of these two great water-beetles are elongate, 

 six-footed creatures, with powerful jaws (Fig. 1), 

 presenting no sort of resemblance to the beetles themselves ; 

 both are carnivorous and extremely voracious, dealing de- 

 .struction to great numbers of their companions in pond- 

 life. The ordinary spiracles being aborted, their respiration 

 is conducted through certain projections at the tip of the 

 tail, which are thrust above the surface to imbibe air. 

 Having passed a comparatively short life in the larval con- 

 dition, the insect quits the water, and, forming a cell in the 

 damp margins of the pond, there effects its change to the 

 pupal state. In due time the beetle is produced from this, 



Fig. 1. — I-.irva of Hydrophilna piceua. 



at first 6oft and pale, but acquiring, after a few days' expo- 

 sure to the air, its normal colour and consistency. The 

 female Hydrophilus forms a marvellous sac for the recep- 

 tion of her eggs. It is composed of a gummy substance, 

 the secretion of which is effected not in or near the mouth, 

 but at the other end of the alimentary canal. A tough, 

 papery bag is formed, which carries a long .spike, and is 

 attached to subaqueous plants. The eggs, about fifty in 

 number, are regularly placed side by side within this, and 

 are thus protected from the attacks of such aquatic creatures 

 as might feel disposed to try the taste of beetles' eggs. 



Another of the Philhydrida, a much smaller insect, of 

 yellowish -brown colour, called Sperchevs emarginatus 

 ( Fig. 2), which used to be found at Whittlesea Mere, and 

 was supposed by many to have become extinct as a British 

 species until recently rediscovered by Mr. T. R. Billups at 

 a certain spot in the neighbourhood of South London, forms 



Fig. 3. — Spercheus emarginatus. 



a bag which the mother carries about on the under surface 

 of her body. This insect, both in the larval and perfect 

 state, is described by the Rev. W. W. Fowler, who has 

 kept and watched the species, as having the peculiar habit 

 of walking on the under-side of the surface of the water 

 with its back downwards, after the fashion of a fly on a 

 ceiling, a thin film of air contained between the body and 



the edges of the elytra seeming to act as a float ; the larva, 

 too, is so completely permeated with air by means of its 

 large trachea- as to be rendered quite buoyant, and to find, 

 apparently, as much difliculty in sinking as a man with a 

 cork jacket on ; so it needs no effort to maintain itself in 

 its inverted position just below the surface. 



Water-beetles, as we have already .said, are not confined 

 to the water, but at night frequently leave their native 

 ponds and enjoy themselves in the air, or migrate to other 

 quarters. >Jo collection of water is so small as not to 

 prove attractive to them ; even cart-ruts that have been 

 converted into so many miniature canals by a heavy rain 

 may soon become tenanted. They cannot boast of any 

 great brilliance of colouring. Yellows of no very con- 

 spicuous hue, browns, greys and blacks, singly or inter- 

 mixed, are the prevailing tints. Some few of the brighter 

 yellow species are spotted with black, and so become rather 

 pretty, and some of the Philhydrida are slightly adorned 

 with spots and patches of a metallic tint something like 

 that of " peacock copper ore," but with these few excep- 

 tions they are a sombre set of insects, and their chief inte- 

 rest certainly lies in the remarkable niodifications which 

 fit them for aquatic life. 



We now pass to the Dipterous fauna of the middle 

 depths. The Diptera, it will be remembered, are the two- 

 winged flies, and none of these in the perfect state inhabit 

 water ; some, however, are aquatic during their two earlier 

 stages. Omitting a few very aberrant forms, there may be 

 considered to be two very distinct types of tlies, one slender, 

 with abnormally long and fragile legs, and with sintennje of 

 moderate length, and frequently tufted or fringed with 

 hairs ; the other stouter and more substantial, with much 

 shorter legs, and antenn;e so inconspicuous as often to be 

 unnoticed. It is to the former of these groups that most of 

 the species whose larvse are aquatic belong. They consist 

 of certain kinds of gnats, midges, and daddy-longlegs, insects 

 whose names are as familiar as household words, though no 

 very exact signification appears to be popularly attached — 

 at any rate to the two former «i these, which are often vaguely 

 used for any minute and delicate flying insect, of whatever 

 nature. Very varied are the habits of the long-legged, 

 long-horned flies : some of them are the causes of certain 

 gall-like excrescences that occasionally disfigure plants, and 

 inside which their larva' live ; the larva' of others, again, 

 live in the earth, especially in damp places, and it is only a 

 few members of the group that are aquatic, and that we have 

 now to deal with. 



It may seem diflicult to conceive of a method by which 

 80 fragile a creature as a gnat, which would be irretrievably 

 damaged by contact with the water, can manage safely to 

 convey its eggs into such a position as will permit the larvae 

 hatched from them at once to get into their proper element 

 Most wonderful, indeed, is the plan adopted. Finding some 

 floating shred of straw, stick, grass, or other such support, 

 the expectant mother rests her two fore-legs on this, allows 

 the next pair gently to touch the water, and crosses the 

 third pair behind to form a sort of vice in which to hold 

 the eggs as they are deposited. Then a long oval egg is 

 lodged in the angle formed by the crossed legs, with its 

 longer diameter vertical ; another, following it, is glued on 

 to the side of the first in a similar position, and so on till 

 some "200 or 300 are fastened into a sort of raft, or 

 rather life-boat, as the mass is curved upwards at each end. 

 Then the little vessel is abandoned to the mercy of winds 

 and wavelets, and so floats about for a few days, benefiting 

 by sun and air, till the growing embryos, finding their 

 quarters too close, push open a kind of trap-door in the 

 floor of the egg and take a dive at once into their watery 

 home. They are qviaint-looking creatures, with a big head 



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