Finding elusive rodents in a warehouse

Ramp up your inspection to find the stragglers

You’ve accomplished a lot in this warehouse. Reduced the rodent population significantly. But there always seems to be a couple of mice left behind. Your customer is getting restless; you need to find and eliminate those last few mice now.

1. Make sure you know where all food products are stored. If your warehouse is a food storage warehouse, you need to know the flow of products through the warehouse: where they enter, how they’re processed, how rejects are handled, product rotation, etc.

   If you’re note dealing with a food warehouse, consider that there could still be stored food present. For example, an office supply retailer also sells break room items such as coffee creamer, sugar, cookies, and snacks. And don’t forget to ask management about the warehouse employees’ lunch room, where coffee supplies are stored, and how trash is handled.

2. Look outside to find the source of rodents inside. The rodents are most likely breeding inside the facility, but they could be coming in from outside. Walk around the outside of the facility looking for rodent entry points into the building such as cracks in concrete slabs or brick, openings around conduits for utility lines, unscreened roof and wall vents, poorly sealed heating and air condition ducts, and spaces around loading cock doors, doors that don’t seal tightly, or doors that employees leave open.

   The best time to conduct an outside rodent inspection is just after dark or about an hour after human activity in the building ends for the night. Consider setting up low-light video cameras with motion detectors on tripods to record rodent activity both outside and inside the warehouse.

3. Look for rodent signs. If you find a suspected rodent entry pint, look closely for rub marks, dark greasy stains that show the rodents’ travel routes. You might find rub marks around pipes, along beams, along baseboards, wherever rodents touch surfaces as they travel.

   Rodent droppings are most numerous along runways, near harbourage sites, and near food sources. Remove rodent droppings and nest material as you find it (after noting the location). This insures that rodent signs found on follow-up visits will be evidence of a new or ongoing infestation.

   The best way to detect rodent urine is with a hand-held UV light. Follow the trail of fluorescing urine to locate rodent entryways into the warehouse and follow the trail back to their harbourage areas. Other liquids like certain industrial chemicals also fluoresce under UV light, so make sure you are tracking rodent urine droplets.

4. Check areas that you might have considered inaccessible before.

   1. Wall and ceiling voids. Look inside wall voids in high probability areas. If you suspect rodent activity inside a wall, inspect the voids. There are a few ways you can inspect voids. You can open up the wall or ceiling, or you can look inside with a borescope (not always possible because of insulation), listen with a stethoscope, or a video contractor may be able to thread a remote camera into and along certain voids. Also check inside drop ceilings and utility runs. An inspection mirror with a telescoping handle is useful for checking in drop ceilings and in unreachable, tight spaces.

   2. The subfloor space. Check floor drains. The concrete around old door drains often crumbles letting pests enter from below the slab. Ask about abandoned sewer lines that can provide entry points for rodents. Conduit, pipe, and refrigeration lines in and under slabs can become breeding and runway sites for rodents. Also check inside floor access pits, rail pits, and the dock floor pit.

   3. The roof. Don’t limit your inspection to the main, ground floor. Rodents may be nesting in attic void spaces. They will climb up conduits, building corners, and gutters to reach the roof where they can enter through rooftop vents and equipment such as ventilation fans and air handling systems.

5. Check these warehouse areas that are particularly susceptible to rodent infestation:

   1. Receiving dock – Food smells, spillage, and open doors attract rodents. Check the dock pit space below the floor.

   2. Return goods storage area – Products in this area are likely to be open or have damaged packaging making them easier for rodents to penetrate. Food products can sit undisturbed in this area for some time.

   3. Refrigeration areas – The enclosed dead space above, and the false floor below, coolers provide voids that can house rodents. Mice can live in the insulation in a walk-in cooler and in the warmth around compressor motors.

6. Consider using a tracking patch. If you suspect rodents are in a certain area of the warehouse but you just can’t find any evidence, place a temporary tracking patch that will capture footprints. Dust a paper-thin layer of a nontoxic powder such as talc, unscented baby powder, powdered clay, or ground limestone onto suspected runways. Check back in a day or two to see if there has been rodent activity.