UC IPM recently hosted a webinar on rat management presented by Dr. Niamh Quinn. During this webinar attendees were able to ask the expert their burning questions about rats and their management. Below are responses to common questions from the webinar.

To view the recording of this webinar, visit https://www.youtube.com/watch?v=IuKU6izZozo. Or visit the Pest Notes: Rats fact sheet that was recently revised by Dr. Quinn. 

Rat Identification

Q: How do I know whether I have a roof rat or a Norway rat?

A: The roof rat (also called the black rat, house rat, or ship rat) is smaller and sleeker than the Norway rat, with a tail that is longer than the head and body combined. Roof rats are agile climbers and usually live and nest aboveground in shrubs, trees, or dense vegetation such as ivy.

The Norway rat (also called the brown rat, sewer rat, or barn rat) is a burrowing rodent that is generally larger and stockier than the roof rat. Their burrows may be found along building foundations, beneath rubbish or woodpiles, and around gardens and fields.

When the two species occupy the same building, Norway rats typically occur in the basement and ground floors while roof rats occupy the upper floors and attics.

Q: How can you distinguish protected woodrats from Norway and roof rats?  

A: Like commensal rats, pack rats (woodrats) consume various food items, including fruits and nuts. An easy way to distinguish pack rats from Norway and roof rats is to visually examine their tails. Woodrats have furry tails, while commensal rodents have scaly and mostly hairless tails. 

Trapping

Q: Should you wear disposable gloves when handling rat traps? 

A: Human scent is not known to have any impact on rat trapping but since rats can carry diseases, it would be best to wear gloves when handling used traps. You should always wear gloves when handling dead rats.

Q: What is pre-baiting and why should you do it when using toxic baits? 

A: Pre-baiting means placing bait in the trap without setting the trigger of the trap. Since rats are neophobic (afraid of new things) doing this will allow them to get more comfortable approaching the trap to get the food or other item (cotton, etc.). Pre-bait for 5 days or so and then set the trap to catch the rodent. 

Q: Can rat traps be reused? 

A: Depending on the type of trap purchased, some are meant to be reused while others are single use. Snap traps, for example, can be used over and over again.   

Q: How can you secure or anchor down rat traps? 

A: Rat traps should be secured down to effectively catch rats and find the traps later. They can be screwed into a piece of wood, such as 2x4 lumber, which you can reuse and easily move traps to new management areas. Putty or tape can also work.   

Two rat traps secured to a tree limb using a piece of wood and tape. Photo by Niamh Quinn, UCCE.

Q: How can you prevent wildlife from being harmed while trying to manage rats?  

A: Trap rats at nighttime when songbirds are not active to prevent them from being caught in traps. When using toxic baits, place them in bait stations to make them less accessible to wildlife.

Q: What should you do with live-trapped rats? 

A: Live-trapped rats must be humanely euthanized or released immediately in the area where they were trapped. Releasing rats is not recommended, as they will continue to cause damage. Animals can be humanely euthanized by a shot to the head if it is legal to discharge a firearm in the trapped area or a firm blow to the head. Drowning is not an acceptable method of euthanasia, and it is illegal under California State law.  

Repellents and toxic baits

Q: What can be used to deter or repel rats? I've heard of using coyote urine, mint, LED lights, and ultrasonic devices.  

A: No plants have been proven to deter rats from an area and high frequency ultrasonic sounds are not effective for controlling rats in homes and gardens. Human or coyote urine or scent do not repel rats.  

Q: Can homemade mixtures be used to manage rats?  

A: Only registered pesticide products can be used to manage rats.You should not try to create your own toxic baits at home with household ingredients. 

Prevention and other management methods

Q: How can you prevent rats from chewing wires in vehicles and other powered equipment?  

A: Use a weighted car cover to dissuade rodents from accessing the engine and chewing wires. To be effective, the cover must touch the ground, forming a seal all around the vehicle.  

Q: Can predators like owls, hawks, or cats effectively manage rats?  

A: Predators, especially cats and owls, eat rats and mice. However, predators in general cannot significantly control animals that are good colonizers and prolific reproducers (of which rats are extremely good examples!). Furthermore, if cats or other would-be predators are fed outdoors, their food serves as a strong attractant and a continuous food source for rats and mice in the area. 

Q: What can home gardeners do to keep rats out of the garden? 

A: Sanitation is fundamental to rat control and must be ongoing. Keep pipes, lumber, firewood, crates, boxes, gardening equipment, and other household goods off the ground. Clean up leaves and fallen fruit in backyards. Thin or remove dense vegetation, such as ivy, around or on homes. Excluding rats from garden beds is very difficult. Fencing or enclosing raised beds with wire mesh may provide some management but it is not guaranteed.  

Q: Should I even attempt to control rats in my backyard if I live in a neighborhood or community where there are lots of rats and my neighbors don't take action? 

A: Successful rat management in a neighborhood does require community-wide effort to remove harborage and food sources. But you can reduce the likelihood of rat infestations or damage to your property if you follow best management practices (i.e., sealing gaps larger than ½ inch, removing wood piles or items stored on the ground, thinning dense vegetation around homes, etc.).  

Roof rat feeding damage to navel orange. Photo by Larry L. Strand.