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Identification

Signs of pests: droppings, frass, smells and damage

Many pests are active at night and stay hidden, so their droppings, frass, rub marks and smells are often the first clues. Clean up droppings safely: never sweep or vacuum rodent droppings, and don't breathe dust from bat or bird droppings.[9][10][3]

The short answer

  • Rodents: droppings, fresh gnaw marks, tracks and greasy rub marks; rats leave gnaw marks about 1/6 inch wide, mice about 1/12 inch.[1][2]
  • Bats: droppings (guano) crumble easily and show shiny bits of insects; mouse droppings don't.[3]
  • Drywood termites: piles of tiny pellets with six flattened sides below small kickout holes.[11]
  • Wood dust: carpenter ants push out coarse, fibrous sawdust; powderpost beetles leave flour-fine powder.[12][5]

Droppings and specks

  • Mice and rats leave droppings along walls, near food and pet food, and in recycling bins; place traps where you find them.[1][2]
  • German cockroaches leave fecal specks, shed skins and empty egg cases where they hide and breed.[14]
  • Bed bugs leave small reddish-brown to black fecal spots and blood spots on bedding and mattress seams.[15]
  • Bat droppings collect below roost entry points, often with stains from body oils and urine. Bat guano crushes easily into shiny insect bits, and it's never white.[3]
  • Raccoon feces can carry roundworm eggs that cause serious illness if swallowed or inhaled.[6]

Pellets, sawdust and powder

  • Drywood termite pellets are elongated with rounded ends and six flattened sides; dampwood termite pellets are football-shaped without clear ridges.[11]
  • Carpenter ant sawdust is coarse and fibrous, often mixed with insect parts, and their galleries are smooth and clean.[12][13]
  • Subterranean termites build pencil-wide mud tubes and fill damaged wood with bits of soil.[16][17]
  • Powderpost beetle frass feels like flour or talcum powder; deathwatch beetle frass feels gritty; false powderpost beetle frass is the coarsest and packed tightly in the hole.[5]

Smells

  • A musky odor is common in large or long-term house mouse infestations, and dead rodents in walls cause odors after poisoning, which is one reason UC IPM favors trapping indoors.[2]
  • Heavily infested bed bug areas can have a foul or acrid 'buggy' smell.[15]
  • Odorous house ants give off a strong, rotten smell when crushed.[18][19]
  • Stink bugs, boxelder bugs and multicolored Asian lady beetles release unpleasant odors when crushed or disturbed; vacuum them instead.[20][21][22]
  • Some pantry beetle larvae give infested food a disagreeable odor and taste.[23]

How to inspect

  • Check under sinks, in cupboards and along pipes and wires, where ants and cockroaches travel; a small mirror on a long handle helps in hard-to-see spots.[7][8]
  • Sticky traps set in several locations show where cockroaches are concentrated.[8]
  • In scorpion country, a portable black light helps you find them: scorpions glow brightly under UV light.[4]
  • For drywood termites, clear away pellets near a kickout hole and check a few days later; new pellets suggest an active infestation.[11]

Sources

  1. University of California Statewide IPM Program, “Rats (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/rats/ (accessed 2026-10-06)
  2. University of California Statewide IPM Program, “House Mouse (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/house-mouse/ (accessed 2026-10-06)
  3. University of California Statewide IPM Program, “Bats (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/bats/ (accessed 2026-10-06)
  4. University of California Statewide IPM Program, “Scorpions (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/scorpions/ (accessed 2026-10-06)
  5. University of California Statewide IPM Program, “Wood-Boring Beetles in Homes (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/wood-boring-beetles-in-homes/ (accessed 2026-10-06)
  6. University of California Statewide IPM Program, “Raccoons (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/raccoons/ (accessed 2026-10-06)
  7. University of California Statewide IPM Program, “Ants (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/ants/ (accessed 2026-10-06)
  8. University of California Statewide IPM Program, “Cockroaches (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/cockroaches/ (accessed 2026-10-06)
  9. University of California Statewide IPM Program, “Pest Notes: House Mouse, Publication 7483 (revised July 2025).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnhousemouse.pdf (accessed 2026-10-06)
  10. Centers for Disease Control and Prevention, “How to Clean Up After Rodents.” www.cdc.gov/healthy-pets/rodent-control/clean-up.html (accessed 2026-10-06)
  11. University of California Statewide IPM Program, “Pest Notes: Drywood Termites, Publication 7440 (August 2014).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pndrywoodtermites.pdf (accessed 2026-10-06)
  12. University of California Statewide IPM Program, “Pest Notes: Carpenter Ants, Publication 7416 (August 2009).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pncarpenterants.pdf (accessed 2026-10-06)
  13. Penn State Extension, “Carpenter Ants.” extension.psu.edu/carpenter-ants (accessed 2026-10-06)
  14. University of California Statewide IPM Program, “Pest Notes: Cockroaches, Publication 7467 (revised December 2019).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pncockroaches.pdf (accessed 2026-10-06)
  15. University of California Statewide IPM Program, “Pest Notes: Bed Bugs, Publication 7454 (May 2013).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnbedbugs.pdf (accessed 2026-10-06)
  16. University of Kentucky Entomology, “ENTFACT-604: Termite Control: Answers for Homeowners (revised March 2026).” entomology.mgcafe.uky.edu/ef604 (accessed 2026-10-06)
  17. University of California Statewide IPM Program, “Pest Notes: Subterranean and Other Termites, Publication 7415 (May 2014).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pntermites.pdf (accessed 2026-10-06)
  18. Penn State Extension, “Odorous House Ant.” extension.psu.edu/odorous-house-ant (accessed 2026-10-06)
  19. University of California Statewide IPM Program, “Pest Notes: Ants, Publication 7411 (October 2012).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnants.pdf (accessed 2026-10-06)
  20. Penn State Extension, “Brown Marmorated Stink Bug (revised December 2017).” extension.psu.edu/brown-marmorated-stink-bug (accessed 2026-10-06)
  21. University of Kentucky Entomology, “ENTFACT-444: Boxelder Bugs.” entomology.mgcafe.uky.edu/ef444 (accessed 2026-10-06)
  22. University of Kentucky Entomology, “ENTFACT-416: Asian Lady Beetle Infestation of Structures.” entomology.mgcafe.uky.edu/ef416 (accessed 2026-10-06)
  23. University of California Statewide IPM Program, “Pest Notes: Pantry Pests, Publication 7452 (March 2013).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnpantrypests.pdf (accessed 2026-10-06)

Updated 2026-10-06. Built from sourced records. Spot an error? Tell us.