200 SOME SOUTH INDIAN INSECTS, ETC. (HAP. XXI. 



[Dytiscidae, Gyrinidae, etc.) arc entirely predaceous, as indeed are 



most of the Bugs which live in the water or run along its surface. 



The Coccinellidce, or Lady-bird Beetles, are familiar and 

 extremely beneficial insects, feeding on scale-insects, Aphids and 

 various other pests both in their larval and adult stages. They are 

 generally of very characteristic shape and colour (see plate V) 

 and every cultivator should make himself familiar with their 

 appearance. The adults have, as a rule, red wing-cases spotted 

 with black but the markings are variable and may be wholly red 

 or black, occasionally yellow or dark blue. A very large black- 

 spotted red species is found in the Hills attacking the large Aphid 

 found on pear-trees, and at least one lady-bird (see figure 133) 

 is known to be an enemy of Green Scale-bugs. The mite so 

 common on cholam is attacked by a minute species (Scymnus sp.) 

 which does not apparently touch the mites themselves but devotes 

 all its attention to devouring their eggs. 



I [G. 86.— Parasite "t Diatrcea sp. The small figure shows the natural 

 size. (< Iriginal.) 



Parasites undoubtedly play a much more important part than 

 predators in the reduction of the numbers of any species of insect, 

 and this is largely because parasites as a rule only lay their eggs 

 so that their larvae can feed on their victims, and they are there- 

 lore able to destroy a large number of these latter. It must here be 

 emphasized again that it is by no means every parasite that is 

 beneficial. Probably every species of insect, without exception, is 

 parasitized by one or more other insects and it is obvious therefore 

 thai some parasites must be injurious by their destruction of 

 beneficial insects. Even when an injurious insect is attacked it 

 may be parasitized by two or more different parasites, only one of 

 which is likely to survive, and it frequently happens that this 

 survivor is destructive to a really beneficial parasite and its survival 



