October, ’18] HEADLEE AND BECKWITH: SPRINKLING FILTER FLY 
397 
the egg is almost transparent. From 32 to 48 hours were required 
for hatching at a temperature of 70° F. 
The larvae or maggots are very much like mosquito wrigglers, and 
seem to pass their existence in much the same way. Soon after hatch¬ 
ing they make their way into the film where they thrust their breathing 
tubes through the film itself. The number of larvae on a sprinkling 
sewage filter bed is almost unbelievably large. A single square inch 
of stone has been found to accommodate as many as sixty specimens. 
The larvae are present throughout the filter from top to bottom, but 
they are most abundant in the zone which begins three inches below 
the surface and ends twelve inches below the surface. The length of 
the larval stage ranges from nine to fifteen days under a temperature 
of 70° F. The largest active larva taken at any time in this study was 
9.2 mm. long. 
Transformation to the pupa takes place in the location where the 
larvae fed and developed. The pupa, of course, does no feeding and is 
able to move only by jerking its abdomen. The pupa is about 6 mm. 
long, exclusive of the breathing tubes, and requires from 20 to 48 hours 
to complete development at 70° F. 
Control 
The habits of the adult fly are such as to preclude the control of the 
species through the destruction of the mature form. Nothing short 
of covering the filter with screening which has been treated with a 
substance similar to tanglefoot could be depended upon to destroy the 
adult. The shutting off of the air supply, which would result from 
covering the filters in this way was thought by the engineer in charge 
to be undesirable from the standpoint of the effective operation of 
the filter. Furthermore, the cost of such an installation would be 
large and the length of time the netting would remain effective would 
be limited. 
The problem of control seemed therefore to narrow down to a ques¬ 
tion of destroying the fly in its immature stages. In view of the fact 
that the immature stages of the fly, with the exception of the egg, are 
passed in the film, which is the active agent in the purification of the 
sewage, it seemed necessary to secure an agent, which would be select¬ 
ive in its action in destroying the immature stages of the fly and not 
seriously injuring the other components of the film. A considerable 
number of chemicals was tried in all cases with a view of determining 
the minimum dosage for the fly and its effect on the life and activity 
of the other elements of the film. The tables which follow will serve 
to show the results. 
