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- 
tomophthoreae, 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 hyphse 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 
