PestDecoderDecode a clue

Evidence guide

Damage and gnawing

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

Record the clue before interpreting it

Photograph the entire damaged item and a close-up. Record material, height, fresh debris and whether damage returns.

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

  • Paired tooth grooves versus exit holes
  • Hollow or blistered wood
  • Irregular grazing versus clipped fibers
  • Fresh debris or repeated damage
Handling boundary

Damaged wiring, structural wood or contaminated food should not be treated as cosmetic. Isolate the area and seek qualified help.

Read the full safety guide

Common candidates

These candidates are not ranked until location, scale, pattern, context and timing are added. Open a profile to see confirming and contradicting evidence.

high concern

House mouse

Mus musculus

Small smooth tapered droppings along edges, fine gnawing and shredded nesting material near food routes.

DroppingsHoles and openingsSounds and movement
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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
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high concern

Roof rat

Rattus rattus

Slender rat-scale droppings and nighttime movement in attics, rafters or elevated routes.

DroppingsHoles and openingsSounds and movement
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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
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high concern

Drywood termite

Kalotermitidae

Uniform hard pellets in small piles directly below tiny wood openings, often recurring after cleanup.

Frass and pelletsWings and swarmersHoles and openings
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medium concern

Carpenter ant

Camponotus spp.

Coarse mixed wood shavings below a slit or crack, often with large ants and moisture-damaged wood nearby.

Frass and pelletsWings and swarmersHoles and openings
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medium concern

Powderpost beetle

Lyctinae and related groups

Tiny round holes with flour-like powder accumulating below unfinished or stored wood.

Frass and pelletsHoles and openingsLarvae and grubs
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high concern

Old house borer

Hylotrupes bajulus

Larger oval exit holes, coarse packed frass and feeding sounds in softwood framing.

Frass and pelletsHoles and openingsLarvae and grubs
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low concern

Varied carpet beetle

Anthrenus verbasci

Hairy banded larval skins and irregular grazing damage in lint, wool, feathers or stored natural fibers.

Shed skinsLarvae and grubsDamage and gnawing
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low concern

Clothes moth

Tineola bisselliella and Tinea pellionella

Smooth pale larvae, attached silk cases or webbing and clipped natural fibers in dark garment folds.

Webbing and silkLarvae and grubsDamage and gnawing
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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
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low concern

Firebrat

Thermobia domestica

Mottled tapered insect with three tail filaments recurring near a hot, humid appliance or boiler zone.

Shed skinsDamage and gnawing
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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.

RodentCockroach

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.

RodentRodent

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.

RodentRodent

Open comparison

Side-by-side decision

Termite frass vs. carpenter-ant debris

Drywood termite pellets are uniform and hard; carpenter-ant debris is mixed and fibrous, often with insect fragments.

Wood pestWood pest

Open comparison

Side-by-side decision

Drywood vs. subterranean termite signs

Drywood termites push pellets from wood; subterranean termites preserve humidity with soil-connected shelter tubes.

Wood pestWood pest

Open comparison

Side-by-side decision

Powderpost beetle vs. old house borer

Exit-hole diameter and frass texture are decisive: powderpost signs are tiny and flour-like; old-house-borer signs are larger and coarser.

Wood pestWood pest

Open comparison

Source basis