Record the clue before interpreting it
Photograph the full pattern and a close-up before cleaning. Note whether marks sit on seams, travel edges, cabinet hinges or entry points.
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
- Color and edge shape
- Raised material versus absorbed stain
- Seams, corners or travel routes
- Eggs, skins or droppings nearby
A stain alone cannot diagnose a pest or a bite source. Do not use skin symptoms as the primary identification method.
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.
Bed bug
Cimex lectularius
Ink-like fecal spots, pale cast skins, eggs and flat reddish insects concentrated along bed or furniture seams.
German cockroach
Blattella germanica
Pepper-like spotting, small ridged egg cases and nighttime activity clustered near food, water and heat.
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.
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
Bed bug vs. carpet beetle cast skins
Bed-bug skins preserve a flat insect outline with legs; carpet-beetle skins are hairy and often banded.
Open comparison