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What You Can Learn From the Calling Cards Rats and Mice Leave Behind

An engineer at heart who knows how to get rid of unwanted furry animals.

Droppings and urine trails are how rats and mice communicate with each other. What signs of their presence have you seen?

Droppings and urine trails are how rats and mice communicate with each other. What signs of their presence have you seen?

Why Are Mice and Rats So Messy?

There are probably no animals that defecate and urinate more often than mice and rats (up to 100 times per day), and there are probably no animals that are so indiscriminate about where they make their toilets. But why are these common house rodents so messy? What impels them to leave their waste in places that alert us to their presence so we take measures to eliminate them?

It turns out, scientists tell us, that droppings (which you can see) and urine (which you can smell) are the way rats and mice communicate with each other about food supplies. A rodent actually prefers food that has been contaminated with another rodent's body waste. That keeps humans from consuming the spoiled food supply, of course, but it also lets the next rodent know that the food is safe for rodents to eat.

And not just to gross you out, it is important to know that mice and rats eat the feces of other mice and rats. This means that if the first rodent is carrying a food-borne infection, such as E. coli or Salmonella, future rodents will acquire it to, resulting in more and more furry brown visitors who can infect everyone in your household, unless you make cleaning up rat droppings a priority.

What Droppings Tell Us About the Best Placement of Traps

Droppings can tell us a lot about the best place to set out traps for mice and rats. It's never a good idea to set out a trap in the middle of a pile of droppings. If the droppings are dry, you're too late. But if you use your knowledge of the facts that (1) rodents leave droppings where they find food, (2) rodents like to gnaw their way into feeding sites (it keeps their teeth sharp), and (3) rodents travel in straight lines, you can find the ideal place to put out a mouse or rat trap.

A mouse or a rat will make (if you pardon the mixed metaphor) a beeline for a food source from its place of shelter. It will then mark the path for other mice and rats with its droppings and urine as it travels to and from safety to food. The path laid down by mouse and rat droppings points you to the wall where mice and rats come in and maybe even shows you the way to the hole that lets them in. That's the place to put out your traps--preferably two traps at the same location so the mouse or rat can't just hop over them.

What Droppings Tell Us About the Kind of Rodent Population We Are Dealing With

It's only commonsensical that more droppings indicate more rodents requiring more traps, about 6 traps per rodent to be sure of getting the population under control before adults can reproduce. But the size and variety of droppings tell you what traps will work best.

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If you have both large and small droppings, you have both large (adult) and small (juvenile) rodents. You'll need traps in different sizes to be sure of capturing both adult and juvenile mice and rats and dispatching them humanely. You don't want a rodent just to get a paw or its tail caught in the trap.

Moist droppings typically are less than 3 or 4 hours old. If all the droppings are moist, you have a new rodent infestation, which means you may have a new opening into the room.

And if the pattern of droppings changes after you change the placement of a stored food item, chances are that is the rodents' favorite food. This is the food that will make the best bait.

How to Locate Urine Trails

Mice and rats also mark the paths to food and safety with urine. These drops are invisible to humans without the help of black light.

The black light you use to locate rodent trails needs to have a 700–800-watt bulb. It should emit a beam at least 6 inches (15 cm) wide. It is easier to use a plug-in, rechargeable black light so you don't have to worry about batteries going dead.

Fresh rodent urine fluoresces bluish-white. Dry rodent urine glows yellowish-white and fades with age. Rodents tend to dribble rather than splash, so there will be either small elongated droplets in a line or a pool of droplets that coalesce together, but any evidence of splashing is evidence of another animal (or human).

Where do you look for urine trails? Look on floors, walls, boxes, pallets, or fabric. Remember, rodents travel in straight lines. This helps you avoid misidentifying cleaning agents as rat urine—but chances are that your nose will take care of that problem for you.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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