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 Funct of INSECTS, REGARDED AS 
ALLIES oF Man. 
Many microscopic fungi attack insects, both living 
anddead. 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, gece 
or sometimes Sporendonema muscae or —egnia eran” 
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), 
'  Spheria 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 
