INSECTS AND OTHER ORGANISMS 417 



drop into the rich food-supply, complete their growth, and 

 when mature increase and multiply at an alarming rate. 

 Members of another order of Arachnida, the Chernetida 

 (" false-scorpions "), also are often carried relatively long 

 distances by flies to whose feet they cling with their small 

 but conspicuous '' pedipalps " which resemble in their form 

 the pincers of a miniature lobster. It is also worthy of 

 notice that insects take at least a subordinate part in helping 

 the dispersal of creatures belonging to a very distinct group 

 of animals, the Mollusca. Some interesting examples of 

 such association are given by H. W. Kew (1893), and the 

 majority of them refer to the carriage of freshwater molluscs 

 by aquatic insects which are able to fly and thus carry the 

 shell-fish from one pond or stream to another. Thus 

 species of the bivalves Sphaerium and Pisidium have been 

 found clasping, between the margins of the two valves of the 

 shell, the foot of the water-scorpion {Nepa cinerea^ Fig. 85) or 

 the large water-beetle Dyticus marginalise while these insects 

 were flying through the air. Water-snails and the little 

 fresh- water '' limpet " {Ancyliis fluviatilis) also can obtain 

 aerial transport by crawling on to the elytra of water-beetles 

 and adhering there by the " sucker " action of the foot ; in 

 this way new ponds and streams can be colonised by these 

 molluscs and the range of their species extended. In such 

 and in numberless other ways do insects come literally into 

 close touch with other creatures, and in the course of their 

 usually brief lives take their share in weaving the vast 

 intertwined complex of vital connections that has been well 

 named the " web of life." 



2 H 



