A rodent inspection must aim to locate any signs of infestation and then identify the species, determine the extent of the infestation, locate potential harbourages and entry points and then use this information to plan a treatment program.


There are 14 signs of rodent activity to check for

  • sightings of live and dead rodents
  • faeces (droppings)
  • evidence of gnawing
  • burrows
  • runways
  • tracks in dust
  • grease marks
  • urine stains
  • rodent sounds
  • reaction of dogs and cats
  • smell – indication of rodent activity (mice) or of dead rodents
  • damage to stock
  • stock piles of food (hoarding)
  • piles of indigestible food products (eg nut shells)

One tool that may aid in detecting rodent urine on incoming goods and in locating runways and entry points during an inspection is the use of a black (ultraviolet) light.  However, as with any detection tool it has limitations and requires understanding on how to correctly interpret the information from what you observe.

Longwave ultraviolet light (350-405nm) is used for detection of many items that fluoresce

  • otherwise ‘secret’ markings placed on many items from banknotes to arm stamps at discos.
  • to detect changes in cases of forgery and carpet repair
  • to identify natural verse synthetic blue diamonds and other gems
  • it is used to find results in some laboratory techniques
  • items may be laced with a fluorescent powder to detect leaks (similar use to DETEX BLOX)
  • bodily fluids may be detected by UV light (as in the CSI shows)
  • rodent urine and hair may be detected by ultraviolet light.

The detection of rodent contamination by black light is based on the phenomenon of rodent urine showing blue-white to yellow-white fluorescence when viewed under black light. The fresher the stain the more blue will fluoresce. Urine stains on food bags, containers, floors, etc. while invisible in white light, retains their fluorescence and are readily discernible under black light. Furthermore, rodents urinate when in motion and their paths are visible under black light in characteristic “droplet” pattern or trails. Rodent hairs show a blue-white fluorescence.  Rodents have oily hair that is UV reactive, leaving smudge marks where they travel.

However, some cleaning products, bleaches, packaging glues and adhesives also fluoresce.


  • fresh rodent urine fluoresces bluish-white.  Dry it fluoresces yellow-white, duller with age.
  • the pattern is important – a large area with splashing at the edges is probably not from a rodent – rodents urinate as they run, so look for larger drops becoming smaller in a run line.
  • rodent hairs fluoresce bluish-white and can be found in infested areas on product and runways.
  • avoid false positives – some cleaners and lubricants fluoresce.  Other methods of inspection and the pattern of the fluorescence are important.
  • ‘black’ lights are most effective at night
  • the torch may have to be held close to the surface (150-250mm) to detect the fluorescence.


  • provides evidence of contamination of incoming goods
  • confirming rodent entry points and runways
  • confirming areas of high activity aiding optimum placement of baits and traps
  • monitoring activity in sensitive accounts
  • tracking the movements of one or a few rats that may be difficult to find
  • provide evidence to the customer of rodent activity and any building or hygiene improvements required

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