I have often observed that the whole bulk of larvae, when the pond is almost 

 dried up, .are metamorphosed into pupae in the course of very few days and often 

 probably in the course of a few hours; in these very small water reservoirs, black 

 with the pupae, often lying in layers over each other, the temperature rises in the 

 sunshine to about 28 C.; the pupae-stage lasting only one or two days. 



Further I have observed ponds which had a good deal of water in 1918, and 

 from which enormous masses of 0. communis were then hatched, but were dried up in 

 1919 during the whole of spring, and only in July got a decim. of water in the 

 deepest holes of the bottom. These holes were often formed by the cattle plodding 

 in the mud. In these very small water reservoirs a small part of the enormous 

 egg masses which covered the whole bottom was hatched; in the course of only 

 eight or ten days, by the drying power of the sunshine, in our hottest summer- 

 months, the whole metamorphosis was finished; at last the little water-mass was 

 packed with pupae, these being so numerous that they lay in layers over each 

 other, pressed together to suffocation; the whole mass is in a constant circulation, 

 the deepest layer always trying to reach the surface. In the greyish dried, up sur- 

 face of the pond these small holes shone black from the masses of black pupae. 



The huge masses of larvae in the last stage as well as the pupae are of course 

 extremely good as food for many lower animals. Whereas the pupae of Chirono- 

 midae when they come up to the surface from the great depths of the lakes are 

 a welcome prey to the dikeswallows, I do not know of any insect-eating bird 

 which has learned to catch its food in the ponds teeming with mosquito larvae or 

 pupae; at all events I have never disturbed our singing birds on the drying mos- 

 quito-ponds; for the blackbird, which comes in late autumn and winter to the 

 same ponds to search for the larvae of Trichoptera, the mosquito larvae are prob- 

 ably too small. On the other hand, the surfaces of these ponds, near the hatching 

 time of the mosquitoes, are covered by pondscaters which dig their huge probos- 

 cis into the fat forepart of the pupae. As most of the pondscaters are wingless, we 

 must admire the speed with which they are able to find these small and often 

 sheltered ponds. But also different Dytiscidae more especially of the genera Colym- 

 betes and Rhantus as larvae prey almost exclusively upon O. com /n urns-larvae; the 

 eggs are laid in early spring, and it is interesting to see how these larvae in their 

 development keep time, so to speak, with the mosquito larvae; they are hatched 

 as larvae at the same time as these and they are ready to pupate a little after the 

 mosquito larvae have metamorphosed into pupae. It is very interesting to find these 

 ponds which, a few days before, have delivered the whole mass of mosquitoes to 

 another element, teeming with black and white coloured Dytiscid-larvae. An- 

 other fat morcel would have been desirable before pupation, but such a one can- 

 not now be obtained, the mosquitoes all being out of their reach; now they 

 have only one prey upon which to satisfy their hunger, viz. their own comrades. 

 This is exactly what happens, woe to the larva which, when the mosquitoes have 



