Cockroach Control in San Francisco, CA

Local Context

Two Species, Two Routes: One Comes Up the Drain, the Other Through the Wall

German cockroaches (Blattella germanica) travel with people and stay indoors. They arrive in a grocery bag, a cardboard box, a used appliance or a moving load, then settle into the warm, tight spaces near food and water: the motor housing of a refrigerator, the void behind a dishwasher, the hinge of a cabinet door. In San Francisco flats and apartment buildings they spread from there through the plumbing chases and party-wall cavities that connect units up, down and sideways. That is why treating one kitchen in an eight-unit Edwardian building rarely holds.

American cockroaches (Periplaneta americana) come the other way. They live in sewers, drains, sub-areas and old brick basements, and they enter through floor drains with dried-out trap seals, gaps at the sewer lateral and open sub-area vents. They are the large ones people find in a basement laundry, a back stair or a ground-floor bathroom after a wet stretch. They say nothing about the household. They say a plumbing or sub-area opening is available.

The mixed-use block keeps both running. Winter lows here sit in the mid to upper 40s, nowhere near cold enough to break a cockroach cycle, and the standard San Francisco arrangement puts a restaurant or a corner market on the ground floor with flats stacked above it and an old basement below. Grease, warmth and a shared plumbing stack sit under the residential units, so the pressure a tenant on the third floor is feeling often starts two floors down and outside their lease. There is no seasonal reset to wait out. What ends an infestation is bait carried back to harborage, a growth regulator that stops juveniles reaching breeding age, and closing the route the population is using.