II.] PROTECTION OF PLANTS BY INSECTS. 35 



base, and a small, sweet, pear-shaped body at the tip. 

 In consequence, it is inhabited by myriads of a small 

 ant, which nests in the hollow thorns, and thus finds 

 meat, drink, and lodging all provided for it. These 

 ants are continually roaming over the plant, and con- 

 stitute a most efficient body-guard, not only driving 

 off the leaf-cutting ants, but, in Belt's opinion, render- 

 ing the leaves less liable to be eaten by herbivorous 

 mammalia. Delpino mentions that on one occasion 

 he was gathering a flower of Clerodendron fragrans, 

 when he was suddenly attacked by a whole army of 

 small ants. 



I am not aware that any of our English plants are 

 protected in this manner from browsing quadrupeds, 

 but not the less do our ants perform for them a very 

 similar function, by keeping down the number of small 

 insects, which would otherwise rob them of their sap 

 and strip them of their leaves. 



Forel watched, from this point of view, a nest of 

 Formica pratensis. He found that the ants brought in 

 dead insects, small caterpillars, grasshoppers, cercopis, 

 &c., at the rate of about twenty-eight a minute, or 

 more than one thousand six hundred in an hour. 

 When it is considered that the ants work not only 

 all day, but in warm weather often all night too, 

 it is easy to see how important a function they fulfil 

 in keeping down the number of small insects. 



Some of the most mischievous insects, indeed — 

 certain species, for instance, of aphis and coccus — 

 have turned the tables on the plants, and converted 

 ants from enemies into friends, by themselves develop- 

 ing nectaries, and secreting honey, which the ants 



D 2 



