34 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



modified ; and observation shows that they are pro- 

 vided with numerous contrivances for the better 

 protection of their tenants. 



Gall-insects are f)reyed u^ion by numerous insects. 

 Some live in the galls, feeding on the gall structure, 

 ousting, cuckoo-fashion, the legitimate owner, which 

 is killed; many feed on the larvae. Now the gall- 

 larvse can only feed when the galls are soft and 

 juicy. The spring galls, as a rule, are always in 

 this condition, but then the larvae feed up very 

 fast and become perfect insects in a very short 

 time. The autumnal galls, on the other hand, 

 have a much longer duration. iVt first they are 

 soft, as must of necessity be the case if the larva 

 is to feed; but after it has become full-fed the 

 galls turn quite hard, if not woody, in texture. It 

 is evident then that if the parasitic or inquiline 

 flies are to obtain a footing in the galls they must 

 attack them when in their soft condition — for their 

 ovipositors are unable to pierce the hard woody 

 galls, while the cuckoo-flies can, like the gall-larvae 

 themselves, only eat the galls when in their early 

 soft state. To x>i'otect the gall-flies at this period 

 we find numerous contrivances. Many are minute 

 and not readily seen ; so as to make them less 

 visible the catkin-galls assimilate in colour with 

 the catkins, being greenish when young, and bro^vn- 

 ish when old. The pilosity on some of them, e.g.y 

 Andricus pilosus^ adds to their resemblance to the 

 catkins. A few are concealed in the leaf-buds, 

 e.g., AjMlothvix coUaris, where they can scarcely be 

 noticed. There is no doubt also that the x:>ractice 

 of some of the softer galls of dropi)ing to the 

 ground, after the larva has reached maturity, is a 

 valuable aid in i^rotecting it ; for it reduces greatly 

 the time during which it is exposed to attacks. 

 These galls also when on the tree are green, but 

 before falling become dark in colour, and thus are 

 hidden effectually on the dark soil. The galls of 

 Neurotcrus again do not become fully developed 



