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Tech Talk – Using Black Light to Detect Rodent Evidence

By William Kolbe, BCE

The amino acids in rodent urine and hair will fluoresce (shine) when uncovered to sure wavelengths of sunshine present in black gentle, generally known as ultraviolet gentle. Black gentle shines a deep blue and sometimes is used with creative poster shows. Different substances like starch, bleached sack fibers, optical bleaches, glues and adhesives, dyes, some cleansing brokers, and lots of industrial chemical substances additionally will fluoresce, so care and follow is required to successfully use this inspection and diagnostic device as a PMP.

See more: What color is mouse urine when it dries

Rodents are incontinent. This implies they defecate and urinate as they transfer about consistently. Not like people, as quickly because the rodent physique produces excreta, it’s expelled. Pest management practitioners know most urine and droppings are deposited the place the rodents spend most of their time and the place they journey. A visible inspection utilizing a flashlight will usually reveal rodent droppings, urine staining and different proof. The black gentle can be utilized to corroborate suspected contamination and rodent presence.

After visually figuring out probably rodent entry factors alongside a construction’s perimeter, use a black gentle to find out whether it is certainly getting used as a runway. Black gentle inspection of premises is much less correct as mud, grime, particles and cleansing brokers can obscure urine fluorescence. The sunshine is simplest for inspecting packages, saved supplies and bagged items.


  • Rechargeable black lights needs to be absolutely charged when used, to permit for the strongest potential illumination.
  • Black lights needs to be utilized in darkish, or subdued lighting areas. If sensible, flip overhead lights down, or transfer items being inspected to darker, much less well-lit areas.
  • Transfer the black gentle unit over the floor being examined, holding it as shut as potential with out damaging the unit.
  • Maintain the sunshine at an angle, permitting visible observations to be made.
  • Urine staining is probably discovered between bins and luggage.


  • Rodent urine fluoresces blue-white to yellow-white when dry, bluer when recent and turning into paler with age.
  • Rodent hair fluoresces blue-white.
  • Starches, detergents and soaps present as an excellent blue-white stain.
  • Bleached fibers in sacking appears to be like blue-white.
  • Pitches and tars look yellow.
  • Glues used to seal cardboard bins radiate a mustard yellow coloration.
  • Human urine appears to be like like rodent urine, however might be current over bigger areas.
  • Lubrication oils and grease fluoresces green-white to blue-white to brown.
  • Rodent urine usually will seem as a skinny line of dots, drops or streaks working between cartons and luggage, particularly on vertical surfaces.
  • Rodent urine usually could have tail drag marks via the fluorescing deposit.
  • Rodent urine has little to no symmetry to its deposit. If a deposit seems giant, patchy and evenly distributed, it’s not rodent urine.

PRACTICE MAKES PERFECT! Apply utilizing the black gentle on items of cardboard or packaging identified to have been involved with rodents. You additionally may go to a pet retailer and ask the supervisor should you can follow close to the pet mice or rat containers (earlier than or after hours in fact). You would possibly land a contract checking for rodent escapees!

Use the black gentle on cartons and luggage identified to come back from uninfested areas and cardboard identified to have been uncovered to bleach, glues and different chemical substances to turn into accustomed to what different supplies and chemical substances appear to be when fluorescing.

LIMITATIONS AS A TOOL. Perceive black lights have limitations as a device. Black gentle urine proof needs to be used as a primary indicator of potential rodent contamination, or to corroborate different suspected proof. It shouldn’t be used as a stand-alone, diagnostic device to reject items as we all know different substances fluoresce.

Kolbe is the director of technical and coaching companies, Viking Pest Management, Bridgewater, N.J. His profession in pest administration began in June 1974 after graduating from the College of Delaware.

This Tech Speak article was initially revealed within the September 2016 version of PCT journal.

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