PARASITIC FUNGI AND MOULDS. 47 



a damp wall (Fig. 19). When beer or sweetmeats turn 

 sour, it is the work of a fungus." 



VII. PARASITIC FUNGI OF INSECTS, REGARDED AS 

 ALLIES OF MAN. 



Many microscopic fungi attack insects, both living 

 and dead. We have all seen the bodies 

 of flies still, sticking to the window- 

 pane or curtain, and surrounded by a 

 species of aureole formed by the growth 

 of a fungus, Penicillium racemosum, 



- 



or sometimes Sporendonema muscce or 



Saprolegnia ferax, of the family of Oospores (Figs. 



20, 21, 22). 



Cordiceps attacks certain caterpillars of the genera 

 Cossus and Hepialus, when they are buried in the 

 sand before their metamorphosis into chrysalides, and 

 kills them by the development of its mycelium in 

 their tissue. These caterpillars may often be found, 

 bearing on their backs a fungus longer than them-, 

 selves (Fig. 23). 



Sphceria militaris, a parasite to Bombyx pityocarpa, 

 the caterpillar found on pine-trees, represents one of 

 the few fungi which may be regarded as beneficial 

 to man, since it destroys multitudes of these cater- 

 pillars, and thus neutralizes the ravages caused by 

 their devouring the young shoots and pine needles. 

 In the Antilles there is a wasp called the vegetable 



