Perhaps the most important human aspect of the European reptiles is the presence of numbers of insect-eating forms. In the warmer parts of Europe every wall or patch of rock seems alive with lizards in the summer sunshine, and these must play a not inconsiderable part in the keeping down of noxious insects.
Omitting a great number of other groups, we may say something about insects, which are of enormous importance in human life, both directly and indirectly.
It has been shown of late years that many insects are the sole means by which certain very deadly diseases are transmitted from man to man, or from one animal to another. Almost every few months a new announcement of an insect-carried disease is made, but the most important forms are the following:--Mosquitoes and gnats transmit such diseases as malaria, yellow fever, and more horrible diseases still, due to the presence in the blood of small parasitic worms. Tsetse flies carry sleeping sickness, and also transmit the very fatal fly disease of domesticated animals, a fact which has been and is of great importance in the settlement of Africa. In the case of most diseases there seems to be a close connection between one particular species of insect and a particular disease.
Mosquitoes and gnats are very abundant in many parts of Europe, and the forms belonging to the genus Anopheles, which carry the germ of malaria, are widely distributed. In parts of the Mediterranean area their presence is associated with the prevalence of malaria, which has existed there for a prolonged period, and is believed by some to have had an important bearing upon the fates of the ancient civilisations of the Mediterranean basin.
The regions in Europe affected, or seriously affected, by malaria are diminishing yearly. This is now due to conscious efforts, but a similar process has been going on probably for a long period, for many obscure diseases, notably "ague," seem to have been forms of malaria. Their disappearance seems to be due to drainage, which diminishes the breeding places of the mosquitoes, and also to the progress of agriculture, for ponds which form on rich, well-manured land are apparently unsuited to mosquito larvæ. The subject is of great geographical importance, for the spread of man over the surface of the globe, and the progress of civilisation must have been influenced in all time by the prevalence of fly-borne disease. Such diseases have hitherto been the greatest obstacle in the way of the civilisation of Africa.