506 Observations on Habits and Parasites of Common Flies 
Empusa disease. 
The mode of infection in this disease is at present not well understood, 
and the writer hopes that his observations and experiments may help 
to carry us a step further. 
Brefeld (1873) successfully inoculated the spores of Empusa muscae 
under the skin and obtained germination of the gonidia on the surface 
of the fly. 
Olive’s (1906) experiments with an allied species, E. sciara, indicate 
that infection may occur in the very young larvae on the surface of 
excreta, before they burrow into its depths. Gussow (1913) infected 
flies by painting them with water containing spores, and he found 
also that he could infect flies by bringing them into contact with dead 
flies covered with spores. He suggests that “it is not unlikely that the 
flv becomes more susceptible to the disease as it grows older, while 
newly emerged broods are more or less resistant.” 
Hesse (1914) thinks that “the theory, expressed in published works, 
that the fungus, E. muscae , attacks the fly from the exterior does not 
seem very credible.” He succeeded in infecting flies by allowing them 
to feed on empusa spores and also by allowing them t® feed on spores 
derived from cultures made from flies dead of the disease. These 
cultures, it should be noted, produced a fungus identical with M. 
racemosus. 
Bernstein (1914) also succeeded in infecting flies by the same means. 
He seems to think that the larvae may become infected, but says that 
“the question as to whether the disease can be transmitted from fly 
to fly in the adult stage is still unsettled, and experimentally it has not 
proved successful.” Bamsbottom (1914) has up to the present failed 
to cultivate empusa from a single spore, and seems inclined to doubt 
whether the Mucor, which usually grows in cultures from infected flies, 
has any connection, as Hesse asserts, with Empusa. 
Thaxter (1888) in America found Empusa muscae on several species 
of hover-flies (Syrphidae) and records its occurrence in L. caesar and 
C. vomitoria, and states that two other species of empusa, E. sphaero- 
sperma and E. Americana occasionally attack house-flies and blow-flies. 
The former species destroys insects belonging to several orders. Lucas 
(1908) exhibited to the Entomological Society of London “a spike of 
the grass Molinia caerulea with dead Syrphids, Melanostoma scalare 
Fabr., attached by the parasitic fungus Empusa muscae, found on 
Esher Common, October 3, 1908. Most were attached by the point of 
