34 ON PLANTS AND INSECTS. [LECT. 



of acacia : this tree, if unprotected, is apt to be stripped 

 of the leaves by a leaf-cutting ant, which uses them, 

 not directly for food, but, according to Mr. Belt, to grow 

 mushrooms on. The acacia, however, bears hollow 

 thorns, while each leaflet produces honey in a crater- 

 formed gland at the 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 roam- 

 ing over the plant, and constitute a most efficient 

 body-guard, not only driving off" the leaf-cutting ants, 

 but, in Belt's opinion, rendering the leaves less liable to 

 be eaten by herbivorous mammalia. Delpino mentions 

 that on one occasion he was gathering a flower of Clero- 

 dendron 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. 



