250 A BOOK OF INSECTS 



Normally, the mature blade, or " trap," lies flat, or nearly 

 so, and is more or less continuous with the stalk ; but if 

 an insect ventures upon it and comes into contact with 

 one of the sensitive bristles, the two lobes spring together 

 with considerable force, and the intruder is imprisoned 

 beneath the interlocking marginal spines. The whole 

 contrivance reminds one of an iron gin or rat-trap. Darwin 

 found that each leaf is able to capture and digest two, or 

 perhaps three, insects in succession ; but not more. It 

 then withers, and its place is taken by a younger leaf. 



Insects are also killed by fungi. In the autumn, dead 

 house-flies may often be seen sticking to walls and window- 

 panes. Their bodies are greatly swollen, and are sur- 

 rounded by a quantity of white powder. Such insects 

 are the victims of Empusa muscce — a fungus which attacks 

 flies of various kinds. All the internal organs are gradu- 

 ally invaded and destroyed ; and when death results the 

 minute spores of the fungus (the white powder) are ejected 

 in all directions. They are capable of infecting other 

 flies ; but how this is accomplished, and in what manner 

 the Empusa is carried on from one season to the next, are 

 points which are at present uncertain. 



Other species of Empusa are known, one of which 

 (E. aphidis) infests aphides, and exercises an important 

 check upon their increase. Another (E. grylli) attacks 

 grasshoppers and crickets ; while E. auliccc occasionally 

 causes a high rate of mortality among caterpillars. 



The remarkable objects known as " vegetable cater- 

 pillars " are the burrowing larvae of large swift-moths 

 (Hepialidce) from Australia and New Zealand, which 

 have been done to death by fungi belonging to the 

 genus Cordyceps. The fungus first replaces every part 

 of the insect's body, and then sends up a long fructifying 

 shoot through the soil. The caterpillar of our own garden 



