210 THB entomologist's record, 



degree. The floating islands and floating trees, borne by ocean and 

 river, would carry, probably, hundreds of insects for one mammal, and 

 it is well-known that large numbers of insects, whose larvje live in 

 solid timber, have been introduced into countries thousands of miles 

 distant from their native habitat. 



Wallace observes {Geoy. Dist. of Animals, i., p. 38) : " Most insects 

 have the power of existing for weeks or months without food, and some 

 are very tenacious of life. Many beetles will survive immersion for hours 

 in strong spirit ; and water a few degrees below the boiling point will 

 not always kill them. We can, therefore, easily understand how, in the 

 course of ages, insects may become dispersed by means which would 

 be quite inadequate in the case of the higher animals. The drift- 

 wood and tropical fruits that reach Ireland and the Orkneys ; the 

 double cocoa-nuts that cross the Indian Ocean from the Seychelle 

 Islands to the coast of Sumatra ; the winds that carry volcanic dust 

 and ashes for thousands of miles ; the hurricanes that travel in their 

 revolving course over wide oceans, all indicate means by which a few 

 insects may, at rare intervals, be carried to remote regions, and 

 become the progenitors of a group of allied forms." 



The importation of certain Colcoptera into distant lands by the 

 influence of man, leads one to point out that species of other orders of 

 insects have been similarly introduced, and are in some instances 

 leaving their mark on the fauna of the country. The introduction of 

 Sesia tipnliformis, Pieris rapae, and Porthetria dispar, from 

 Europe into America, are not only matters of fact, but matters of 

 considerable economic importance, since these insects have com- 

 mitted considerable damage in many parts of their adopted country. 

 The number of foreign insects that have been found in the neighbour- 

 hood of the docks of our large British ports is evidence of the importa- 

 tion of insects into this country. The oriental cockroaches — Stilopycjia 

 orientalis and Phyllodrovtid yninaiiica — which abound in houses, 

 are very old importations into this country, whilst L'ancJilora maderae, 

 Periplanefa americana and Periplandd australasiae have quite 

 recently made their appearance, evidently introduced with imported 

 produce. The larvfc of UeliotJiis amiiyera are introduced every year 

 in tomatoes (propably from America), and from the Canary Islands 

 the larvns of the Noctuid moth, Prodenia litfora/is, have also been 

 introduced in tomatoes. Many similar cases might be mentioned, but 

 they are rather outside the scope of our enquiry, and the examples 

 cited have only been given to show the influence of man on the 

 dispersal of some insects. 



It might be supposed from the above that many insects would 

 be almost cosmopolitan, and have a very wide range, but this is not so. 

 Certainly a few insects arc almost world-wide in their distribution, and 

 others, again, have a very great range, but, as a rule, the habitat of a 

 particular species is more or less restricted, and oven in the case of 

 dominant species with great natural powers of dispersal, their sedentary 

 range is often of comparatively small extent. This is essentially 

 due to two causes : (1) Food — many species of inseois being 

 restricted to a particular species, or, at most, a particular genus of 

 plants. (2) Climatic conditions — which kill oft' (particularly in the 

 winter), the progeny of those insects that migrate from subtropical 

 to temperate regions, owing to the inability of such progeny to pass 



