Q-
I service one of the schools in San Francisco and they have found a
number of little "worms" swimming around in several of the commodes. What are they and what can we do about them?

A-
The "worms" you sent are the larval (maggot) stage of the black
scavenger fly (family Sepsidae). The larvae live in excrement and various types of decaying organic materials. The adults are common flies that are often found near materials where the larvae breed. Since it is not likely the
adult flies would have access to the contents of the commode or sewer line, I
suspect that there may be a plumbing problem at the school. Possibly
there is a break in the line somewhere giving the adult flies access to the
excrement. The larvae will easily breed in the sewer sludge and will
work their way back into the commode. As a pest control operator there is
nothing you can do about this problem except to advise the school
officials. You certainly can't spray any pesticides into the commodes to kill the maggots. Once it is determined where the adult flies have access to
the sewer sludge, then they can be stopped at that point using mechanical
controls such as repairing any breaks in the line.