38
THE ESSEX NATURALIST
characters. It is the difference in the habits of these closely allied
species which are so clearly marked, although their eggs are also
different. Two types of A. maculipennis occur in England; one,
messeae, breeds in the fresh water of inland ponds and streams;
the other, atroparvus, mainly in brackish water in coastal areas,
but it may be present in smaller numbers in inland areas. It is
considered that only atroparvus is responsible for transmitting
malaria in England, and it is the only important carrier of the
malaria parasite in Northern Europe.
As in the case with all indigenous mosquitoes and other
aquatic insects, their numerical prevalence is largely governed by
two factors—the extent of suitable grounds for the development
of immature stages and the available food supply for the adults.
As these two types of Anopheles maculipennis feed almost en-
tirely indoors, it follows that in areas where suitable breeding
grounds are numerous and domestic animals such as pigs, horses
and cattle are also numerous, both these types may be present in
very large numbers.
The larvae are found chiefly where there is an abundance of
aquatic vegetation and where green algae, such as Spirogyra, are
plentiful. The larvae are never found in highly polluted water.
The females of this species pass the greater part of their adult life
in dwellings. As soon as they emerge from the pupal stage, they
usually enter houses, either animal or human, in search of food
and shelter. They leave the shelter to lay their eggs, returning
again when this has been done. When another batch of eggs is
mature, they sally forth again.
To a certain extent, A. maculipennis in England are zoophilic
(preferring the blood of animals other than man). They seldom
or never attack in the open air. In areas where they are numerous,
for every single specimen found in a human habitation, hundreds,
and sometimes thousands, may be observed hanging from old
cobwebs, in cowsheds, pig-styes and stables.
Atroparvus do not leave the animal houses during the late
autumn and winter. They continue to take blood meals through-
out this period, but at more widely spaced intervals than in
summer. When the atmospheric temperature is 70° F. or over,
a blood meal is digested in about forty-eight hours, but when the
temperature is 40° F. or less, it will not be completely digested
for several weeks.
In 1919, Grove, Acting Entomologist to the Local Government
Board, made some observations on the prevalence and habits of
Anopheline mosquitoes in England, and the Great Wakering area
was one of the three he selected for his observations. He showed
that adults of A. maculipennis never entirely disappear through-
out the whole year, but with the appearance of the first brood in
early June, there was a sudden rise of population, and the peak
was reached in September. During this period, males and females