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those of Gronholthegn ; the Mochlonyx ponds, those of Store Dyrehave, of Gripso, 

 of Hestehave and of Suserup. To these many regular observations I can add many 

 accidental ones, gathered on excursions often undertaken for quite different purpos- 

 es. In almost all localities the life history of the mosquito is on the whole the same. 



When the ponds in the time from about i/ix to 15/x get the first insignificant 

 volumina of stagnant water, the first Culicin larvae which appear are those of C. morsi- 

 tans. The quantity of water, in which the eggs are hatched, is often extremely 

 small, only some few liters; the height of the water is so inconspicuous, that the 

 larvse are unable to swim, living the first days of their life as creeping animals, 

 winding themselves over the diatom-covered withered, yellow grasses which cover 

 the bottom of the ponds. As the water rises during the autumn, and the waterline 

 reaches eggs lying above the first waterline, new eggs are hatched. If heavy show- 

 ers fill the little water basin in the course of a few days, almost all the eggs are 

 hatched simultaneously, and the larvae are almost all of the same size during the 

 growth. If the filling of the basin takes place slowly through a long time, egg por- 

 tion after egg portion is seized by the water line and it then happens that newly 

 hatched larvse are found with fullgrown ones. 



In the time from about Vx to about Vxn the larvae grow up, pass the three 

 ecdysis-stages and are commonly fullgrown before the ponds are covered with ice. 

 During the whole autumn the C. morsitans larva is the most common of all our 

 mosquito larvae, and in most of the ponds it is the only one occurring at that time 

 of the year. 



It often happens, as in 1919, that a little rain in the beginning of October 

 fills the water basins; 'in the course of a few days the C. morsitans larvae are hatch- 

 ed. They grew up to the second ecdysis, then in November we got a period of 

 frost, and the pond froze to the bottom; then the whole larva material died out; 

 when the ponds were thawed again in the latter part of November, not a single 

 larva could be found. Then when snow and rain in December had filled the water 

 basin to the brim, new lots of eggs were hatched, and new larvae appeared. As 

 many of these mosquito ponds are extremely shallow, it often occurs that a good 

 many freeze to the bottom; in this case all the C. morsitans larvae died and when 

 in early spring the basins were again filled with water and snow, other mosquito 

 larvae especially O. communis took the place of C. morsitans. Then we had an op- 

 portunity to observe the very peculiar phenomenon that these ponds, when freezing, 

 are filled with thousands of C. morsitans larvae; whereas, when again thawed 

 up, they only contain those of 0. communis. This was more especially the case in 

 the winter of 1918 with almost all the ponds in North Seeland; in a mild winter 

 f. i. in 1920, when the covering of ice was but slight and the ponds open in Fe- 

 bruary, the wintering of larvae is a much more common phenomenon. But whether 

 the winter is severe or mild, it is a rule that in April May we hardly ever find 

 the larvae of C. morsitans in the larva swarms of 0. communis; undoubtedly very 

 many of the C. morsitans larvae die out during the winter; and this is, I suppose, 



