PestDecoderDecode a clue

Inspection route

Basement and crawlspace pest clues

Cool damp routes, foundation gaps, drains and structural wood concentrate lower-level pests and rodent evidence.

Inspect in this order

Start where evidence is most likely to remain undisturbed. Photograph scale and placement before cleaning, then establish a clean baseline only when the material can be handled safely.

  1. Check foundation edges and utility entries.
  2. Inspect sill plates and wood-to-soil contact.
  3. Map moisture before treating insects.
  4. Photograph tubes, droppings or debris without disturbing them.
Avoid this shortcut

Do not enter unsafe crawlspaces or disturb extensive contamination.

Common candidates in this location

Location helps prioritize candidates, but it does not identify a pest by itself. Use a physical sign and companion clue before making a treatment decision.

high concern

Norway rat

Rattus norvegicus

Large thick droppings, broad gnawing and lower-level routes near foundations, drains or burrows.

DroppingsHoles and openingsSounds and movement
Read evidence profile
medium concern

Oriental cockroach

Blatta orientalis

Shiny dark adults, larger droppings and egg cases concentrated in cool wet lower-level routes.

DroppingsEggs and casesOdors
Read evidence profile
medium concern

American cockroach

Periplaneta americana

Large droppings or dark capsules near drains and humid utility routes, often with a large fast adult sighting.

DroppingsEggs and casesShed skins
Read evidence profile
high concern

Subterranean termite

Rhinotermitidae

Mud shelter tubes, soft or hollow wood and equal-length swarmer wings near soil-connected routes.

Wings and swarmersHoles and openingsDamage and gnawing
Read evidence profile
low concern

Silverfish

Lepisma saccharinum

Silvery tapered body, three tail filaments and irregular surface grazing in cool humid paper or storage areas.

Shed skinsDamage and gnawing
Read evidence profile
low concern

Springtail

Collembola

Large clusters of tiny specks that spring when disturbed and disappear as the moisture source dries.

Larvae and grubsSounds and movement
Read evidence profile

Evidence types worth checking

Droppings

Shape, ends, texture and placement can narrow rodents, cockroaches and bats without touching the material.

7 candidate profiles

Inspect this clue

Holes and openings

Diameter, edge quality, material and debris below an opening can distinguish insect exit holes, rodent routes and wildlife entry.

8 candidate profiles

Inspect this clue

Sounds and movement

Time of day, route height, rhythm and weight can narrow rodents, squirrels, bats, insects and plumbing-related noise.

6 candidate profiles

Inspect this clue

Damage and gnawing

Surface scraping, paired tooth marks, hollow wood, clipped fibers and food-package holes are high-value contextual clues.

12 candidate profiles

Inspect this clue

Stains and smears

Fecal spotting, rub marks and blood-like stains gain meaning from placement, solubility and nearby physical evidence.

5 candidate profiles

Inspect this clue

Odors

Musty, oily, ammonia-like or sewage-associated odors are supporting clues only and should be tied to a physical source.

8 candidate profiles

Inspect this clue

Build a repeatable baseline

Record the date, exact position and a scale reference. If cleanup is safe, note whether the sign returns in the same route, below the same opening or near the same resource. Repeat location can be more informative than color or a single photograph.

Source basis