Page:Popular Science Monthly Volume 66.djvu/287

Rh The two troublesome species are Culex sollicitans and C. cantator. A third species, C. taniorhynchus is also a migrant, but occurs in much smaller numbers and does not fly so far. The fourth, C. salinarius does not seem to migrate. Except the last, all these species lay their eggs singly in the marsh mud, not in water, and these eggs will maintain their vitality for months during the summer and remain unhatched during the winter. But when they become covered in summer by a spring tide or a heavy rain they hatch within an hour or two, and millions of wrigglers will be found on a marsh after a storm, where none were seen the day before. In a week these wrigglers are ready for the change to pupa and adult. After the adults have hatched, the first warm sultry night sends swarms numbering millions over the surrounding country. Few of these ever get back and none that leave the marsh finally ever reproduce their kind. In C. sollicitans only the females migrate and all those that were examined proved sterile; the migratory instinct replaces the desire to multiply. In C. cantator both sexes fly; but the males drop out after a few miles have been covered, and the females are sterile as a rule; a few exceptions have been found.

It might seem that having said so much, I had placed the problem of control beyond reasonable hope of practical solution; but the statements are yet incomplete and were left so to bring out forcibly the fact that it is no local matter: it is one with which the state must deal comprehensively. In truth not ten per cent, of that vast marsh area breeds mosquitoes at any time, and even a breeding area is not uniformly bad. The mosquito demands water free from fish or predatory insects of all kinds, that shall remain for at least a week. As a rule wherever tides go, the little species of Fundulus or 'killifish' will go and where they go no wrigglers can exist. Wherever fiddler crabs inhabit a marsh area, and there are thousands of acres so inhabited, their holes drain it completely and afford no chance to breed. It is usually at the edge of the highland, where the tide water works in through grass so dense that it bars fish and fills depressions, that the mosquitoes get their best chance and in a number of surveyed areas it was only the edge of the marsh that was reported dangerous. Other danger spots are the irregular, rather high marshes rarely covered by tides, which dry out completely at times, killing all aquatic life, and then fill all depressions by a heavy storm. Cat-tail marshes when they are at all dense are safe from mosquito breeding.

A very thorough survey of the entire salt marsh area determined that not over ten per cent, of it is at all dangerous, and the question arose, what can be done to make that portion safe. Of course any scheme that provided for the reclamation of the marshes and made them available for agricultural or other industrial purposes would also