Signs of a Cockroach Infestation: What to Look For

Cockroaches are nocturnal and excellent at staying hidden — which means by the time you see one during the day, the infestation has often already grown to a significant size. German cockroaches in particular only venture into open areas during the day when population density has become so high that competition for harborage forces some individuals out. Knowing the subtler signs of activity — before you see live roaches in plain sight — allows for earlier detection and much easier treatment.

Droppings

Cockroach droppings are one of the most reliable early indicators of infestation. They vary by species:

• German cockroach droppings: Very small — about 1mm — black to dark brown specks resembling ground pepper or coffee grounds. Found in large quantities in harborage areas: inside cabinet hinges, in the corners of cabinet shelves, along the tops of door frames, behind appliances, and in drawer corners. High concentrations of small dark specks in kitchen or bathroom areas are a very strong indicator.
• American and Oriental cockroach droppings: Larger — up to 2mm — cylindrical with ridged sides and blunt ends. Found in basement areas, under sinks, near drains, and in crawlspaces.

Egg Cases (Oothecae)

Cockroach egg cases are purse-shaped capsules containing multiple eggs:

• German cockroach ootheca: Light tan, about 8mm long, containing 30–40 eggs. Females carry them until just before hatching — finding one indicates recent reproductive activity. May be found glued to surfaces in harborage areas.
• American cockroach ootheca: Dark reddish-brown, about 8mm, containing 14–16 eggs. Cemented to surfaces in protected areas.
• Oriental cockroach ootheca: Dark reddish-brown, about 10mm, containing 16 eggs. Found in protected, humid areas.

Empty, hatched egg cases (lighter in color, open at one end) indicate an established, reproducing infestation that has been active for some time.

Musty or Oily Odor

Cockroaches produce pheromones and other secretions that create a distinctive musty, oily, or musty-sweet odor. This odor is most noticeable in heavily infested areas — inside infested appliances, inside heavily infested cabinets, or in rooms with large American or Oriental cockroach populations. If a cabinet or appliance has an unusual musty smell that was not there before, it warrants inspection.

Shed Skins (Cast Exoskeletons)

Cockroaches molt — shed their exoskeleton — multiple times as they grow from nymph to adult. Each molt produces a shed skin that remains in the harborage area. Finding pale, translucent cockroach-shaped exoskeletons in cabinet corners, under appliances, or in other harborage areas indicates an active infestation with reproducing nymphs.

Smear Marks

In areas with high moisture, cockroaches leave brown smear marks along surfaces they travel repeatedly — along the junction where walls meet floors, along the inside bottom edge of cabinets, and on surfaces near water sources. These marks are more common with American and Oriental cockroaches than with German cockroaches.

Damage to Food Packaging

Cockroaches chew through paper, cardboard, and thin plastic food packaging. Finding gnawed corners on cereal boxes, pasta bags, or other pantry items — particularly with fecal contamination nearby — is a sign of kitchen cockroach activity.

Where to Inspect

Focus inspections on warm, humid, dark, and food-adjacent areas:

• Under and inside the refrigerator — particularly the motor compartment and the drip tray
• Under and behind the stove — especially the area between the stove and the wall
• Inside the dishwasher — particularly around the door gasket and under the bottom rack
• Inside cabinet hinges and the back corners of cabinet shelves
• Under the sink and around plumbing penetrations
• Behind and under the microwave and toaster oven
• In basement floor drain areas (American and Oriental)

A flashlight and mirror are useful for inspecting tight spaces. If you find any of the signs described above, see our article on what to expect from professional roach treatment for next steps.