f line. "I 



Searle, The Pond and its tnhabitanis. 19 



THE POND AND ITS INHABITANTS. 



{Continued .) 



By J. Searle. 



{Read before the Field Naturalists' Club of Victoria, i^th Jan., 1917. 



Aquatic Insects. 



The water flea salready described spend the whole of their 

 lives in the water, but there are other inhabitants of the pond 

 which, thoiigh the}' are born there, and spend their early lives 

 swimming in its waters or crawling over the water-])lants, end 

 their existence as inhabitants of the air. Among these may 

 be mentioned the water-beetles, dragon-flies, water-bugs, caddis- 

 flies, may-flies, mosquitoes, &c. All these are hatched from 

 eggs laid in or on the water, or attached to water-plants near 

 the surface. Some of these insects, like the dragon-fly, on 

 reaching maturity leave the water for all time, spending their 

 lives in the air " hawking " after smaller insects. Others, like 

 the beetles and some of the bugs, spend most of their time in 

 the pond, preying on the other inhabitants, leaving the water 

 at night-time only, to indulge in flight, courtship, or migration 

 to another pool. They are often attracted by the light of the 

 electric street-lamps, and on summer nights may be collected 

 in great numbers around the base of the poles supporting these. 

 The largest of these insects is Hydrophilus, a dark olive - 

 green beetle one and three-quarter inches in length. The 

 female beetle constructs a cocoon in which she encloses fifty 

 or sixty eggs. This cocoon, though thin, is perfectly water- 

 tight, so that the eggs, which would be killed by submersion 

 in water, are kept dry and warm, though the cocoon may be 

 attached to the under side of a leaf of a water-plant. In order 

 that the eggs and the newly-hatched larvae may be supplied 

 with air, the beetle constructs a tube, or ventilating shaft, at 

 one end of the cocoon ; the end of this tube is bent upwards, 

 and projects above the surface of the water. Thus provided 

 for, the eggs are left to hatch out, which they do in three or 

 four weeks (in an aquarium). When hatched, the young soon 

 break through the cocoon and begin their predatory existence. 

 Though rather slow of movement, having a fleshy, tapering 

 body and short, thin legs, they levy a heavy toll on the smaller 

 creatures of the pond, especially the small water-snails, whose 

 shells are readily crushed by the formidable-toothed jaws of 

 the larva. When fully grown they measure about 2-1 inches, 

 and are dark brown in colour. Though living and feeding in 

 the water, these larvae breathe air, which they obtain by 

 elevating their bodies so that the two short, hair-like breathing 

 tubes by which it is terminated are above the surface of the 

 water. These tubes convey the air to the tracheae which 



