A HISTORY OF SURREY 



markings, may sometimes have the green replaced by bright mulberry ; 

 this is a very pretty variety. It is not known if the descendants of a 

 mulberry coloured larva will also be mulberry or whether it is merely a 

 ' sport,' but the two forms may be found feeding side by side. Cimbex 

 lutea and Nemafus turgidus also have occasional red forms ; these abnor- 

 mally coloured larva? are very delicate and difficult to rear. 



Many species have brightly coloured larva? which feed in company 

 and are very conspicuous. They protect themselves from birds by their 

 abdominal glands which emit a powerful and disagreeable odour and 

 (probably) by a disagreeable taste. The Croesus genus furnish good 

 examples of this peculiarity, especially C. septentrionalis, which gives out a 

 disgusting and fetid smell when disturbed. The Dineura genus, notably 

 D. stilata, are protected in the same manner. Nemafus abdominalis on the 

 other hand, an inconspicuous green larva, is very fragrant, its scent resem- 

 bling that of the lemon verbena. 



Solitary feeding larvas generally trust to protective colouring for 

 their safeguard and are often very difficult to detect even when they are 

 known to be on a given plant. Such is Camponiscus luridrventris, an 

 absolutely flat green larva which lies stretched out on the undersides of 

 alder leaves on which it feeds. It resembles some kind of scale insect 

 rather than a caterpillar. Others imitate bird droppings, for instance 

 Eriocampa ovata, which is covered with a white flaky substance disguising 

 it very effectually. The flakes can easily be rubbed off and disclose a 

 pale green larva, but they are renewed and intensified after each moult. 



All these devices however effectual against birds seem powerless to 

 repel the attacks of ichneumons and parasitic Diptera to which sawflies 

 are exceedingly subject. Every species suffers from one or more of these 

 parasites, and it is chiefly by their agency that in this country sawflies do 

 not often multiply sufficiently to do serious damage, as has sometimes 

 happened in Germany where swarms of Lopbyrus pint have destroyed 

 whole pine plantations. 



Gallflies form a very large group of insects and much still remains 

 to be discovered concerning their economy. Wherever oaks and roses 

 thrive there will the gall makers and their inquilines and parasites abound. 

 Galls vary infinitely in appearance, texture, structure and position ; they 

 may be situated on any part of a plant including the roots, may contain 

 one or many inhabitants, may drop off the plant in autumn or remain 

 growing with the twig long after the fly has escaped. They may be 

 smooth, spiny or warty ; green, white, brown, yellow, pink or purple ; 

 regular or irregular, round or spindle shaped, globular or ovoid ; woody, 

 succulent or stringy. Mr. Cameron in his Monograph, after mentioning 

 the theories held by different authorities on the origin of galls and how 

 they are produced, concludes that as regards the Cynipida ' there is no 

 evidence that the venom emitted by the insect when laying has anything 

 to do with the origin of the gall, and that as observation shows that the 

 mechanical irritation produced by the birth and growth of the larva is 

 the primary factor in gall genesis, we may fairly conclude that the theory 



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