402 LAND ANIMALS 



species of certain larger groups occurring in the tropics and subtropics 

 with the number in other regions, we find: 8 - 



Tropical and 

 Subtropical Non-tropical 



Locustids 2726 1120 



Acridids 2811 1842 



Dragonflies 2096 921 



Pentatomids 3675 1560 



In this connection, it should be remembered that the species of the 

 temperate zones are much better known. There are in South America 

 4.560 species of butterflies in 272 genera ; in the entire palaearctic re- 

 gion, Europe and Asia north of the Himalayas, 716 species are known. 

 Within the radius of an hour's walk at Para, Bates collected 700 species 

 of butterflies, 83 all Europe possesses about 400 species. In Venezuela, 

 78 species of sphingids were collected at electric lamps, almost three 

 times as many as are found in all Europe. 84 Not all insect groups are 

 similarly distributed. Thus bees, gall insects, may flies, and caddis flies 

 are fewer in the tropics than in the higher latitudes. 



Ants are especially characteristic of the insect life of the tropics, 

 and the termites are still more so. We know 2888 formicid species from 

 the tropics, from the temperate zones only 1055 ; s2 the termites are 

 confined mainly to the tropics. Ants and termites have a powerful in- 

 fluence not only on the rest of the insect world but also on the biota 

 as a whole; even man may be helpless against them. The highly devel- 

 oped method of rearing the broods, together with the protective struc- 

 tures that are situated everywhere, above and under the earth in the 

 most varied types and sizes, may well offer the explanation for their 

 overwhelming numbers of individuals; the ability of ants to thrive on 

 the most diverse food, and of termites to feed on wood or other parts of 

 plants, gives them an advantage over other animals; both are pro- 

 tected also by soldier castes. The hosts of ants may explain the fact 

 that other predatory and carrion insects, like the carabids, the staphy- 

 linids, and necrophorids, are reduced in numbers, as reported from all 

 parts of the tropics by various observers. 85 Wherever the armies of the 

 infamous driver or army ants arrive (Dorylus in Africa and India, 

 Eciton in tropical America), there arise an energetic flight and a great 

 massacre; Vosseler 80 estimated that such an ant colony collected 

 1,600,000 insects from a single field in 10 days. These ants are also dan- 

 gerous to larger animals, if for any reason they are unable to escape. 



The enormous numbers of ants and termites occurring in the tropics 

 has led large animals of varied origin to live on these small insects; 



