Rats in the rowhouse wall, or roaches by the back door?

What should you do before a technician comes to a Philadelphia rowhouse?

Clear the space under the sink and in the cellar, bag food, and photograph what you see. Do not seal the holes or set traps in a hurry.

The technician needs to see how the pest is getting in, and a hole sealed with foam or steel wool before the visit hides the route. A bait or trap left out at random can also teach a rat to avoid the spot. Photographs of the droppings, the gnaw marks and any shed wings help identify the pest before anyone opens a wall.

• Photograph the evidence: droppings, gnaw marks, the trail along the baseboard, shed termite wings.
• Clear under the sink and in the cellar so the technician can reach the back wall.
• Bag food and pet dishes and store them in sealed containers.
• Note where and when: rats are usually heard at night, and roaches show up on the stove after dark.
• Tell the technician about children and pets so products and placement suit the house.

Why do Philadelphia cellars and party walls attract rats and roaches?

Rats follow the drains, the gas and water lines and the gaps around them, and roaches follow moisture, grease and warmth. Old masonry, shared walls and a busy block give both plenty of route.

The Norway rat burrows under slabs and runs along the outside of foundations. A cellar drain with a cracked collar or a gap around a gas line is a common way in, and a rat that finds one can use the same route into the next house. Standing trash in a back alley makes the route worth using.

German cockroaches are the species most often found in Pennsylvania buildings, according to Penn State Extension. They like moisture, grease and the cracks behind an apartment stove, and they travel between units through the same walls and pipe chases. That is why a single apartment is rarely the whole problem, and why the inspection looks at the units either side.