84 THE WORLD OF LIFE 



and here we find the total number of the Lepidoptera in 

 Essex, which is not far from an average county, very nearly 

 the same as its area. The number of species of these 

 insects is also suggestive, in being about one-half greater 

 than the number of flowering plants (ioio) on which they 

 almost all feed in their larval state. We know that many 

 different species feed on some of our commonest plants — 

 as the oak, poplar, elm, nettle, etc. — while some larvae feed 

 on several distinct plants indiscriminately. But probably 

 the larger number feed on one species of plant only, and 

 thus almost all our plants, except the very rarest, afford food 

 for at least one lepidopterous larva. 



Again, just as we found that a selected area of 10 square 

 miles in Surrey had nearly two-thirds of the plants in the 

 whole county, so here we find that a selected area of 10 

 square miles in Essex has nearly two-thirds of the Macro- 

 lepidoptera found in the county. Here, too, we see the 

 result of the dependence of the insects on the plants, the 

 great variety of the latter in Epping Forest (450 species) 

 rendering possible a corresponding variety of the former. 



Coleoptera {Beetles) 



The enormous order of the beetles (Coleoptera) not being 

 exclusively feeders on living plants, but both in their larval 

 and perfect state often feeding on animal food or on vege- 

 table debris, are probably more uniform in their numbers 

 in different areas if not absolutely barren or very highly 

 cultivated. 



Area. Species. 



Great Britain .... 87,500 3260 



Essex ..... 1,530 I0 55 



As it requires perseverance in collecting for many years 

 in order to obtain all the beetles in even a very limited 

 district, I think it probable that the above figures do not 

 so closely represent the actual number of species inhabiting 

 the county as in those given for the plants, or even the 

 moths. 



To show the vast numbers and variety of the insect tribes, 

 I give here the approximate numbers of actually described 

 insects, kindly furnished me by Mr. C. O. Waterhouse 



