Record the clue before interpreting it
Record room, intensity, timing, moisture and whether ventilation changes the odor. Never inhale material at close range.
A useful record includes scale, shape, texture, placement and whether the material returns after a clean baseline is established. Avoid changing the scene merely to make identification easier.
What to note
- Exact source zone
- Moisture or drain connection
- Nighttime change
- Physical signs in the same area
Leave areas with strong sewage, chemical, gas or unknown hazardous odors and contact the appropriate utility or professional.
Read the full safety guideCommon candidates
These candidates are not ranked until location, scale, pattern, context and timing are added. Open a profile to see confirming and contradicting evidence.
German cockroach
Blattella germanica
Pepper-like spotting, small ridged egg cases and nighttime activity clustered near food, water and heat.
American cockroach
Periplaneta americana
Large droppings or dark capsules near drains and humid utility routes, often with a large fast adult sighting.
Oriental cockroach
Blatta orientalis
Shiny dark adults, larger droppings and egg cases concentrated in cool wet lower-level routes.
House mouse
Mus musculus
Small smooth tapered droppings along edges, fine gnawing and shredded nesting material near food routes.
Norway rat
Rattus norvegicus
Large thick droppings, broad gnawing and lower-level routes near foundations, drains or burrows.
Roof rat
Rattus rattus
Slender rat-scale droppings and nighttime movement in attics, rafters or elevated routes.
Phorid fly
Phoridae
Hump-backed side profile, erratic running and repeated emergence near hidden moist decay or plumbing defects.
Drain fly
Psychodidae
Fuzzy triangular wings, weak short flight and adults resting near one persistent wet-film source.
Comparisons that resolve common confusion
Side-by-side decision
Mouse vs. cockroach droppings
Size and surface are the fastest split: mouse droppings are distinct rice-like pieces; German-cockroach evidence is usually pepper-like spotting or tiny ridged material.
Open comparison
Side-by-side decision
Mouse vs. rat droppings
Overall length, thickness and associated damage matter more than color. Rat evidence is substantially larger and heavier.
Open comparison
Side-by-side decision
Norway rat vs. roof rat signs
Vertical location is the strongest household clue: Norway rats favor ground and lower levels; roof rats concentrate signs above.
Open comparison
Side-by-side decision
German vs. American cockroach evidence
German cockroaches cluster in warm indoor harborages; American cockroaches are far larger and often travel from humid utility or drain systems.
Open comparison
Side-by-side decision
German vs. Oriental cockroach evidence
Temperature and level separate them: German cockroaches favor warm appliance voids; Oriental cockroaches favor cool damp lower spaces.
Open comparison
Side-by-side decision
American vs. Oriental cockroach evidence
Both favor damp lower spaces; American cockroaches are reddish, larger and warmer-route oriented, while Oriental cockroaches are darker and tolerate cooler wet sites.
Open comparison