Apart from the blood-sucking flies, there are many other interesting points about the insects of Europe, notably the wealth of beautiful and striking forms which occur round the Mediterranean basin. One of these, which extends northwards and westwards to northern France, is the curious Praying Mantis, a predatory insect belonging to the same order as the locust. It is an eastern form, which, like so many others, has taken advantage of the mild climate of western Europe to extend its range far beyond what we must regard as its natural limits. In France it shows the effect of relatively unfavourable conditions in the fact that it takes some nine to ten months for the eggs to hatch, whereas in hotter countries the process may take place in a few weeks. In the warmer parts of Europe a very striking feature is the number and large size of the members of the locust and grasshopper families, whose shrill noise is so characteristic a sound in, for example, the pastures of Switzerland in summer-time. Among the locusts there occur, in many parts of Europe, those migratory forms which possess that power of periodic enormous multiplication which we have already noted so frequently among grassland animals. The migratory instinct only seems to develop when the numbers have greatly increased in any given locality, and in Europe generally the climate does not permit this to take place. It does, however, occur in the south-east of the Mediterranean basin, notably in the island of Cyprus, in Syria, and also in Northern Africa, where locusts sometimes reach the dimensions of a plague.