Defensive Characters. xxxvii 



Great size, as in Aphilotrix radicis, occasionally puts 

 the larva beyond the reach of the parasite, while the 

 very opposite condition protects by insignificance. 

 Another efifective protection is found in Andrims ciir- 

 vator, v^here the inner gall lies in a large hollow 

 chamber, an arrangement which makes the work of 

 the parasite difficult and uncertain. 



Outside enemies such as tits, pheasants, and squirrels 

 are as much to be feared as parasites. The larvae are 

 defended from these, sometimes by the nature of the 

 outer gall, which in Aphilotrix fecundatrix consists of 

 closely imbricated scales resembling a hop strobile. 

 \x\ A. Siebotdi the outer gall is hard and stony ; in 

 Cynips Kollari and Trigonaspis crustalis, the tannin 

 which is contained in the tissues renders them dis- 

 tasteful. As the galls mature the percentage of tannin 

 becomes less, but the hardening of the epidermic 

 layers which then takes place affords a new line of 

 defence. After the gall has fallen another set of influ- 

 ences secure its safety by the changes they produce in 

 its surface-colouring. The galls of Andricus ostreiis, 

 Btorhiza renum, and many others, are supplied, as 

 Beyerinck has pointed out, with certain hydrocarbon 

 compounds, which absorb moisture and undergo mole- 

 cular changes after they reach the ground ; with these 

 chemical changes the growth of the larva and the devel- 

 opment of protective coloration in the gall take place. 



Cymps Kollari, Dryophanta scutellaris, and a few other 

 gall-larvae and gall-flies, have the power of emitting 

 a disagreeable bug-like odour, which is not sexual, 

 since agamous species possess it, but probably protects 

 the flies to some extent from birds. Certain galls have 

 a fruity and aromatic smell \ the use of which does not 

 ^ Paszlavszky, lVti)i. Ent. Zcit., 1883 p. 130. 



C3 



