NATURAL ENEMIES 63 



But the principal cause of the sluggishness on the part 

 of the house fly in the autumn is the attack of fungous 

 diseases. Sometimes they are found to be dead without 

 any evidence of the cause of death. Later they are 

 seen to be surrounded by a white fungus growth. 



There is a group of fungi belonging to the En- 

 tomophthorese, many of which are parasitic upon in- 

 sects. There are several genera in this group, but the 

 only one which need be considered at present is the 

 genus Empusa. The fungi of this group have been 

 studied by Dr. Roland Thaxter of Harvard University, 

 and it is from his writings that the following state- 

 ments have been drawn. 



The infection of insects by these fungi results from 

 contact with a spore which, adhering to the insect, en- 

 ters its body by means of a fungous thread known as 

 a hypha. The exact method of the entrance of the 

 hypha is not known, but it must be through the thin- 

 ner membrane connecting the body segments and the 

 leg joints, or through the breathing pores. It has been 

 suggested that the spores may be eaten, but Thaxter 

 thinks that this is not the usual means of introduction, 

 since experiments that he has made contradict it, and 

 he finds that as a rule the digestive tract during life 

 does not seem to be penetrated by the fungus. After 

 one of these hyphae has entered the body of the insect 

 it develops with some rapidity at the expense of the 

 softer tissues. It multiplies, not by branching or by 

 continuing to grow, but by the formation of short, 

 thick fragments of various sizes and shapes that are 



