Improve Your Roof Rat Inspections, Treatments with These Tips

It’s not a big surprise that roof rats are typically found in elevated areas. It is right there in their name! They are also called black rats, ship rats and house rats. The tendency to be up high makes them hard to get to. They may be in drop ceilings, high wall voids and almost any other off-ground location. Those locations aren’t easy to inspect and can be even harder to implement control methods.

Of course, sanitation and exclusion are important. By reducing the amount and access to food sources, rodents have to work harder for less. They grow slower, reproduce less often and have higher overall mortality. They may leave the area to more easily find food. Exclusion keeps them out, so they can’t enter and find any food or harborage.

It is easy to say “clean up all the food” and “seal up all the openings.” However, that can never be completely accomplished. There will always be some food source, and there will be openings that aren’t detected or are inaccessible. That doesn’t mean effort shouldn’t be put into fixing openings and removing food. It means working around and compensating for those issues.

THE PROBLEM. All living things need food, water and shelter. So where are the food, water or shelter spots that can’t be removed? By eliminating what can be eliminated, roof rats can be driven to those remaining food areas. Inspections, trapping and baiting can be focused on those problem areas. I was working in a food facility a few years ago that was having issues with roof rats infesting several areas within the plant. They instituted a much more robust sanitation program, and the amount of available food was reduced considerably. From there, we could see where they were traveling to get to the few food sources left to them. There was an intensive period of trapping that significantly reduced their population. That allowed us to focus our time and effort on a few key areas instead of worrying about the entire facility.

At that same site, we had to determine how they were getting in. We couldn’t inspect every inch of the ceiling areas, but from what we could see, there didn’t appear to be a great deal of nesting inside. The facility was in the process of fixing openings and installing exclusion devices. Knowing we were dealing with roof rats, we redirected their efforts from doors on the ground level to the roof and higher openings. During that process, they discovered a skylight (yep, this food facility had skylights!) that was stuck open. They could not fix that immediately; however, they could seal up many other openings they found at the roof level. This drove the rats to the one opening, and we put control equipment around the outside and as close as we could to the inside of the open window. It’s not that the ground floor openings were not important. They were less important than the active pathways on the roof the rats were using to enter.

INSPECTION CHALLENGES. Roofs and drop ceilings are hard to inspect because they are physically hard to get to. They may require extension ladders, lifts, special PPE or finding the one person who has a key to access the areas. That means they get inspected less regularly. There is less light and limited access, all making it difficult to detect and mitigate roof rat activity. Getting traps and bait stations to these areas takes more time and effort than dropping a bait station on the ground or setting a few ground-level snap traps. Roof rats are not going to be in those locations.

Bait stations can be placed outside on flat roofs. Drop ceilings can be more difficult because a heavy bait station may collapse through the ceiling tiles. When placing stations, try to get them in the pathway the roof rats are running along. Of course, this is especially hard when they are running on beams, cables or other conduits. If it is safe to do so and the station can be secured on those surfaces, it’s a great place to target. In drop ceilings, they may need to be placed closer to walls instead of on the tiles.

DROP-CEILING BAITING. Most rodenticide labels state, “Tamper-resistant bait stations must be used if children, pets, non-target mammals or birds may access the bait.” There won’t be many children or pets in drop ceilings, so technically, bait wouldn’t have to go in stations. But there are a few reasons to take the extra time to do that.

• Monitoring — If you throw a bunch of blocks or packs of bait in a drop ceiling, it’s impossible to tell how much they are eating and where they are eating. Putting bait in contained stations means you can track feeding consumption. You can tell where that feeding may be concentrated. Move stations in response to that data.
• Contamination — Labels also typically state, “Do not place near or inside ventilation duct openings. Do not contaminate water, food, feedstuffs, food or feed handling equipment.” If you are putting bait in an elevated area, ask yourself what is below it? Securing the bait in a station prevents rodents from relocating it. Even worse, this prevents it from falling down to food areas or into ducts.
• Replacement — When the infestation is eliminated, that bait should be removed. Rodenticide labels say, “Replace contaminated or spoiled bait immediately.” If loose bait is tossed into a drop ceiling, it is difficult to know which ones need replacing and/or removal. Contained in a station, you know exactly where the bait is and can more easily check it.

TRAP PLACEMENT. Traps should follow the same guidelines as bait stations. Traps can be easier to set in high areas because they are smaller and lighter. Many snap traps can be zip-tied or otherwise attached to beams the roof rats are running along. They can be put in small, tight areas. Traps can be lined up on a section of cable, put in a circle around an opening, scattered in drop ceilings and more. Snap traps also can be used outside on flat roofs. Location is vital for trap efficacy because the rats will not go out of their way to visit a snap trap when they have food and established runways in another direction. If there is a pizza sitting on the counter, you wouldn’t go around it to get to a pizza at your neighbor’s.

In most cases, putting a small amount of food or other attractant on a snap trap encourages rats to visit the trap, especially if many of their other food sources are taken away. Finding which food source is the most attractive to them can be a challenge. Start baiting with all different types of food. You may be putting something different on each individual snap trap. Since they are using drop ceilings as pathways to their food, the closer bits of food on the traps may be enticing. The drawback to using any type of food material is that it won’t last forever. If it sits on the trap for long periods of time, it will get moldy, hardened or unappetizing. The old material needs to be cleaned out and replaced. If traps aren’t checked every week, there may be better options than food.

Editor’s Note: A version of this story first appeared in QA’s sister publication, PCT magazine.