A 365nm UV flashlight reveals what's invisible in daylight — scorpions, rodent urine trails, and pest activity. Here's exactly how to use it and what to buy.
| Target | UV Response | Color | Notes |
|---|---|---|---|
| Scorpions | Glows brilliantly | Bright blue-green | ALL scorpion species; best UV use case |
| Rodent urine (dry) | Glows brightly | Blue or blue-white | Maps rodent runways |
| Bed bug fecal stains | Glows faintly | Dull orange-brown | Supplement to white-light inspection |
| Dog/cat urine | Glows brightly | Bright blue-green | Very effective for finding old stains |
| Cockroach feces | Glows faintly | Pale yellow | Helps confirm harborage areas |
| Live cockroaches or bed bugs | Does NOT glow | — | Use white light for live pest inspection |
| Tonic water (test) | Glows brilliant blue | Vivid blue | Use this to calibrate your UV light |
True UV-A wavelength. Creates genuine fluorescence. LEDs appear nearly colorless (not bright purple). Cost $20–$60. Brands: Escolite, Hausbell, Convoy. Test with tonic water — should glow brilliant blue.
Slightly less effective than 365nm but much better than 395nm. Makes scorpions glow, may miss faint rodent urine trails. Good budget option for scorpion-only use.
The cheap purple-LED flashlights sold everywhere. More visible light than UV. Scorpions glow weakly, rodent urine barely fluoresces. Often mislabeled as "blacklight." Not suitable for pest inspection.
Scorpions are nocturnal and most active 1–3 hours after dark. Complete darkness makes fluorescence visible — even a single ambient light source can wash out the UV glow.
Scorpions appear as bright blue-green glowing shapes. Look under rocks, along foundation walls, in plant debris, and around water features where prey insects congregate.
Arizona bark scorpions enter homes regularly. Shine UV under beds, in closets, inside shoes before putting them on, and along ceiling-wall junctions — bark scorpions are climbers.
Turn off all lights. Ambient light from windows prevents you from seeing faint older stains.
Mice and rats travel the same paths repeatedly. Their urine trails create lines along walls and inside cabinets. A trail of fluorescent spots reveals exactly where rodents are moving.
Use blue tape to mark the floor near fluorescent spots while inspecting. These are exactly where snap traps should be placed. Concentration of fluorescence = the most active runway.