Predation 393 



of plants are also included. Predatory animals that eat other animals 

 are carnivores, and those that feed on plants are herbivores. Some 

 herbivorous animals kill the plants on which they feed by consuming 

 all or most of each individual. Aquatic filter feeders necessarily de- 

 stroy all the diatoms, flagellates, and other algae that they digest, 

 and herbivorous animals on land that feed on small plants may do the 

 same. However, many insects and many ruminants browse lightly 

 over the vegetation in such a way as to allow the plants to continue 

 life indefinitely. We have seen that the grazing of sheep, for ex- 

 ample may trim the grass harmlessly and prevent the invasion of 

 other plants, thus aiding in the development of a healthy permanent 

 turf. 



Usually plants serve as food for animals, but in a very few excep- 

 tional instances the tables are turned, and animals fall prey to car- 

 nivorous plants. In the terrestrial flora these are also known as in- 

 sectivorous plants since insects are the usual prey on land. Plants 

 with this food habit are adapted in various remarkable and intriguing 

 ways to attract, catch, and digest their victims. The sundew 

 (Drosera) for example, has round, reddish leaves provided with hairs 

 that are progressively longer toward the periphery and tipped with 

 glistening drops of a sticky, sweet secretion. When an insect, at- 

 tracted by the color or odor of the plant, alights on the leaf, it sticks 

 fast to this little bit of natural fly paper. The presence of the insect 

 causes the hairs to bend over it; a digestive secretion is produced, and 

 the body of the insect is absorbed. The vase-like leaves of the 

 pitcher plant are filled with water and serve as death traps for other 

 insects (Fig. 10.13). Animals that fall into the pitchers are unable 

 to climb out because of the steep sides and downward directed hairs; 

 they eventually drown and are digested by special tissues at the base 

 of the leaf. Further interspecific relations result from the fact that 

 several protozoans and aquatic insects, including certain mosquito 

 larvae, normally live in the water of the pitchers. In the larger 

 plants of the tropics frogs station themselves at the openings of the 

 pitchers and spiders spin webs across them to secure their take of 

 the insects that stray past. 



Some plants are hunters of even smaller game. Specially adapted 

 bladders of the aquatic bladderwort Utricidaria open suddenly when 

 any plankton organism comes in contact with the trigger bristles; 

 the unlucky plankter is sucked inside and digested. Equally remark- 

 able are adaptations that permit certain predaceous fungi to capture 

 and to consume prey even larger than themselves. One species pro- 



