Rats in the California Home Garden
Part 3: Signs of Rats in Home and Garden
How common are rats as pests in gardens and landscapes? What should you look for as signs that rats are visiting your garden?
Hard statistics about rat populations in urban California areas are almost nonexistent, and estimates of populations vary widely. Everyone seems to agree that most California cities are infested, and rat problems are particularly common in urban areas with mild winters and abundant outdoor habitat, such as palm trees that form persistent skirts of dead fronds or dense-and-impenetrable living canopies.
After more than two decades of gardening and consulting in Southern California, I have concluded that rat damage in vegetable gardens and to fruit on backyard fruit trees is common and prevalent, and much more so than many gardeners and homeowners might realize or want to admit. Rat damage commonly occurs in gardens even when nearby structures aren’t infested. Roof rats may travel relatively long distances of up to about 300 feet to forage. In suburban areas with average lot sizes in Southern California, this means they may visit your garden from at least 3-to-4-houses distance in any direction. With numerous indoor-and-outdoor roof-rat nests possible in almost any suburban neighborhood, the assumption of a radius of 3-to-4 houses, and depending on many factors, this means your garden may be subject to roof-rat foraging from a section of about 20 to 64 or more homes and properties nearest your own.
Rat damage to fruits and vegetables occurs year-round, but is often most severe from late spring to early fall when the majority of fruit trees and warm-season vegetable crops are bearing. The first step in effective response is accurate identification of your pest(s), including species of rat. See the prior articles in this series, Part 1: Norway Rats and Roof Rats, and Part 2: Misconceptions about Rats, for more introductory information.
How do you know if it’s rats? Among all mammalian and animal pests in homes and gardens, the signs left by rats are among the most distinct and recognizable. Rats generally avoid direct encounters with humans but their presence, especially for a population of more than 1 or 2 rats, tends to become obvious over time. In infested neighborhoods, rats may be glimpsed running along walls or utility lines and found drowned in swimming pools or large containers. Dogs and cats may bring a dead rat (or worse, a live rat) home as a gift.
The list of rat signs is a long one. Here are a few of the most common:
– In gardens, the first sign of rats is often chewing damage to almost-ripe and ripe fruits and vegetables. In my experience the tree fruits they prefer include avocados, citrus, and almost any soft fruits including stone fruits such as apricots and peaches, and pome fruits such as apples and pears. Among common garden vegetables and berries, rats seem to prefer tomatoes, corn, and strawberries, but they will eat almost any fruit or vegetable including pumpkins, squash, eggplants, potatoes, and almost any other root crops such as beets and carrots when they are hungry enough. They may eat entire fruits or vegetables but often leave them gnawed or partly eaten. Rats may eat the peels of sour citrus such as lemons while leaving the fruit pith hanging in the tree.
– Unsure whether your problems are caused by rats or squirrels? The next article in this series will provide more information.
– In structures, the first indication of rats is often a scrabbling, scratching, or gnawing sound from the attic or walls. Rats make a distinctive scrabbling as they run, louder and sometimes bordering on mild thumping as compared to the fainter or whisky, scratchy sound of mice. Rat scrabbling is quieter and different than the slower thumping and louder noises typical of raccoons. Rats can make more noise than you would expect for their size. If it sounds like there’s a horse or maybe a human in your attic, it may be a raccoon. If it’s loud but sounds like it couldn’t be a horse or human, the cause is more likely to be rat(s).
– Rats eat a lot and poop a lot. An individual rat may produce 10 to 40 fecal pellets per day. Rat feces are an early and persistent sign of foraging or infestation, and inevitably will be found in and around gardens and structures where rats are active, and scattered in areas where they are feeding or gnawing. Rat feces and urine may carry serious communicable diseases. GardenZeus recommends using a licensed professional to remove any droppings and to decontaminate the area.
– Check the ground closely for rat feces where you have found signs of rat feeding or gnawing. Norway rats produce large pellets, about 1/2-to-3/4-inch long, typically with blunt ends, while roof rats produce smaller pellets about 1/4-to-1/2-inch long, often with one end that is more pointed than the other. Mice produce smaller, narrower droppings. Squirrel droppings may be difficult to distinguish from rat droppings. Over time rat trails or “runs” are marked by urine and feces, while squirrels don’t use runs. For more information, or if you see a few scattered droppings and aren’t sure whether they’re from squirrels or rats, see part 4 of this series (Coming Soon!): Was the Damage Caused by Squirrels or Rats?
– Gnawing: The incisor teeth of both Norway rats and roof rats grow throughout their lives at a rate of up to a few inches per year. Both species gnaw constantly, on almost anything. Rats may gnaw on living and dead wood, plastic, numerous softer substances, and harder substances including cinderblocks and brick. Shredding or debris from gnawing, both indoors and outdoors, can indicate the presence of rats.
– Norway rats dig burrows near buildings and they may burrow in gardens or near garden plants. Entry holes to burrows are typically about 2 to 3 inches wide, and may be mistaken for gopher holes. Look for a rat run with scattered feces leading to the burrow. Gopher burrows usually have multiple or numerous holes and may cover a larger area in comparison to rat burrows, often with some portion of holes plugged with dirt, and without an external run. Norway-rat burrows typically include only one entry hole and one or two exits. Rat-burrow exits may be covered with a layer of soil that is distinct in appearance from the soil plugs used by gophers.
Other articles in the GardenZeus series “Rats in the California Home Garden:”
Part 1: Norway Rats and Roof Rats
Part 2: Misconceptions about Rats
Part 3: Signs of Rats in Home and Garden
Part 4: Was the Damage Caused by Squirrels or Rats?
Part 5 (Planned): Action Plan if You Have Rats or Suspect Rats
Part 6 (Planned): Managing Rats in Gardens and Landscapes