House Mouse

Disney and others have given the common house mouse an image as the fast and clever neighbor who is harmless and only wants to share a bit of cheese before running back into his hole to feed his little family. Would that the real mice who harbor in San Diego homes and fields were so innocuous. Happily, they are also not that clever. Rats are much more intelligent than their smaller cousins, and although they do share many traits, managing mice is a bit different.

The house mouse is gray, and weighs one half to one ounce - tiny! Their bodies are usually 3-4 inches long, with a tail the same length. Large ears, small eyes, and a pointed muzzle typify the  mouse. A female house mouse can have around eight litters of six or more young. It takes only 35 days for the young females to reach sexual maturity. So populations can grow rapidly!

Signs of mouse infestation are less noticeable than rat infestations. Mouse droppings are smaller, rub marks less visible, and they holes they fit through much smaller. As noted in yesterday's blog, they can squeeze through openings around 1/4 of an inch in diameter. Like rats, mice are more likely to invade as the nights get colder, but unlike rats they are more comfortable living in close association with humans. Unlike another, closer relative, the deer mouse, house mice have not been found to carry  Hantavirus. However, they do contaminate our food and can cause damage to home wiring and other parts of the structure. So Mickey has to go.

Control can be difficult, both because of the size of the breeches mice can enter through and because of their rapid reproduction. Still, sanitation, exclusion and trapping can be effective in ridding houses of house mice. While sanitation alone will not solve an existing mouse problem, the lack of proper cleaning is sure to attract them. Keep garbage in tight fitting containers, try not to leave out pet food, and store dry goods in sealed containers. In exclusion, fill any hole where mice might enter. Steel wool is a good temporary barrier, but construction foam is also useful. Check places where pipes and wires enter the house, along the foundation of the house, and check weather stripping at the bottom of all doors. When using traps, if you are dealing with mice rather than rats, glue boards have been found to be most successful. A very tiny bit of peanut butter in the center of the board will help make the trap attractive. For a discussion of other baits, see Monday's blog. When placing traps, put them behind objects, close to the wall, and in a dark corner if possible. By way of note, there are several electronic devices advertised in magazines, which claim to keep mice at bay through Ultrasonic sounds or other means. Be aware that although mice may be initially frightened by these devices, they soon become familiar and will not be a permanent method of exclusion. Obtaining a cat with mouse hunting experience would serve you better.

One last word on rodents and compassion. Although cartoon rats and mice are adorable, and these rodents can make good pets if properly bred and contained, the mice and rats that invade homes in the autumn can bring diseases and should be excluded for safety reasons. If you find your home is infested with these vermin, contact Vector Control and/or a pest professional for help.

Rat Proofing 101

It is not uncommon in San Diego for homeowners, as they are enjoying a balmy twilight on their patio, to see the shadows of furry creatures skittering along fence lines. Trouble in paradise! Rodents are out there, living perhaps in your neighbor's bougainvillea or in the canyon behind your house. With colder nights coming soon, now is the time to secure your house against these critters. 

Roof Rats are the most common home invader in San Diego. They are excellent climbers, often living above ground in trees or in dense ground cover, like ivy. If you see rat droppings around pet dishes or hear noises in the attic at night, chances are good these are evidence of roof rats. The first element of successful rat management is sanitation. Check to be sure lids fit tightly on garbage cans, and if you feed your pet outdoors leave only as much food as the pet will eat at a feeding. Better yet, feed them indoors. To rodent proof your home, check all vents - attic, sub floor, clothes dryer, and rooftop plumbing vents, to be sure they are properly and securely screened. Seal any openings around pipes or cables that go into the house. Cover the chimney with a spark arrester. Repair or replace weather stripping on exterior doors, including garage doors. Check window screens to assure they are in good condition. Trim tree branches and vines away from the house. Since rats are such agile climbers, they often enter attics by climbing trees next to the house. If you have fruit trees, pick the fruit as it ripens - do not let it fall to the ground, where it becomes an attractive nuisance. 

The Vector Control Program here in San Diego County will do a free inspection of the outside of your home upon request. If you have seen evidence of rats on the property, call them at 858-694-2888 or send an email request to vector@sdcounty.ca.gov. They also offer a "Rat Control Starter Kit," which contains a bait station, some rat traps, sample hardware cloth, a DVD and a brochure. Visit their site here  to find out more. Vector Control is quick to point out they are not a pest control service - so if you need professional help beyond what they can give you, call us here at Centurion.

Although many of the exclusion methods outlined here apply equally to mice, these smaller rodents can squeeze through even tinier openings, often fitting through a hole the size of the diameter of a pencil! So even more care is required in mouse proofing your environment. We'll discuss control of the very common house mouse in tomorrow's blog. 

Rodent Quiz Answers

Here are the answers to yesterday's Rodent Quiz. How did you do? Hopefully the answers will help you protect your home against these unwelcome visitors.

1. Rats have poor eyesight, but they make up for this with keen senses of smell, touch, hearing, and even taste. For this reason, when we set traps they are best placed next to a wall - preferably a wall the target rodent is familiar with. Sometimes the traps are not sprung for a few days, as rats are naturally cautious of any new and unfamiliar object or odor. So the answer is (d) - all of the above.

2. Rats can squeeze through an opening as small as (b) 1/2 inch. Keep this in mind as you look for ways to rat-proof your home. An opening the size of a half dollar can be a thoroughfare for rats. And if rats can fit through a 1/2-inch opening, mice can access a much smaller breech. Check the weather stripping on all your doors!

3. According the the San Diego County web page on rat control, a typical rat will travel up to(c) 300 feet to find food. Think football field. They may live in your neighbor's shrubs and eat at your house. For this reason alone it is a good idea to keep pet food indoors.

4. The best protection against rodent infestation is (c) exclusion. The more proactive homeowners are in sealing and screening vents, doors, and other openings that may invite rodents, the less likely they are to have to do any trapping or baiting.

5. Plague is not a historical disease. And it is not the only disease rats may carry into your home. Among other diseases rats may transmit to humans or pets are, leptospirosis, trichinosis, salmonellosis and ratbite fever. According to PCT online magazine, there are (b) 10-15 cases of plague per year in the United State directly related to rodent exposure.

6. The tendency of rats to avoid anything new in their environment is called (a) neophobia. Answer (d), "zenophobia" is a misspelling of "xenophobia," a related human fear of strangers. The other answers are ringers. Neophobia is peculiar to rats. Mice are much more inquisitive.

7. (D) Rodents are always seeking nesting material. Placing a piece of dental floss or string on the treadle of a snap trap has been found to enhance the likelihood of successful trapping.

8. As noted in the answer to #6 above, mice are naturally  more inquisitive than rats (d). Although both are rodents, it is helpful to know some of the basic differences as we try to protect our homes against rodent invaders. As is so often true in pest management, an ounce of prevention is worth a pound of cure. Tomorrow's blog will give more suggestions for rodent-proofing  your house, along with information on free county services.

Rodent Quiz

Here is a timely quiz, not just because it is the Year of the Rat, according the the Chinese calendar, but because we are at the end of summer here in San Diego. As the nights get colder, rodents look for harborage indoors. The more you know about rodent habits, the less likely you are to find them harboring with you. The answers to today's quiz will appear in tomorrow's blog.

1. Rats make up for their poor eyesight with a keen sense of

a. smell

b. touch

c. hearing

d. all of the above

2. Rodents can squeeze through small openings. How small an opening can a rat fit through?

a. 1/4 inch

b. 1/2 inch

c. 1 inch

d. 2 inches

3. About how far does the average rat travel to find food?

a. 50 feet

b. 50 yards

c. 300 feet

d. 300 yards

4. The best protection against rodent infestation is

a. baiting

b. trapping

c. exclusion

d. electric fences

5. Plague is a rodent-borne disease. How many cases of plague are reported each year in the United States?

a. 1-2

b. 10-15

c. 20-30

d. 50-100

6. Rats are naturally wary of new objects or odors. This behavior is called

a. neophobia

b. odophobia

c. zenophobia

d. exophobia

7. Placing a piece of dental floss on the treadle of a snap trap may be effective because:

a. mice practice impeccable dental hygiene.

b. mice are compulsive collectors of odd items

c. the dental floss gives off a scent which is pleasing to rodents

d. rodents are always seeking nesting materials

8. One difference in the habits of rats and mice is that

a. rats carry fleas, but mice don't

b. mice will not infest a home

c. rats love peanut butter

d. mice are more inquisitive than rats

Again, most of the answers are easily Googled. Try to answer without help. Answers appear tomorrow.

Rat Bait Debate

Although there is some consensus among pest control technicians about the effectiveness of various baits in attracting rodents to traps, the issue is still up for some discussion. Homeowners may be interested in knowing, if they don't already, that the stereotypical chunk of cheese is not necessarily the best bait to use. 

First, a discussion of the traps themselves. At Centurion, we have found sticky traps to be most effective when targeting mice, and snap traps most effective against rats. Mice are often so light in weight that they can take bait from a snap trap without triggering the mechanism. Rats are just big enough that they may be able to escape from a sticky trap. So it is important to determine which size rodent you want to target. The best way to make that determination is of course by visual observation. But if you are hearing noise in the attic, chances are good your intruders are bigger than mice. Rodent control may include using poisonous baits, traps, and exclusion. Since poisonous baits are not only dangerous to use but also may result in rodents dying in wall voids, we believe the most successful approach is with traps and exclusion, or sealing out the unwanted guests. We look for points of entry, then seal or screen those points as a critical step in limiting the number of rodents. Next, the traps are set.

In a recent poll of pest professionals nationwide, a majority of the respondents indicated peanut butter as a bait of choice in setting traps. Whether used in a small amount in the center of a glueboard, or applied to the trigger mechanism of a snap trap, peanut butter is a good choice. Other pest control professionals polled utilized a huge variety of baits, including marshmallows, dried fruit, corn chips, walnuts, chocolate, even dried shrimp or strawberry jam. One professional even mixed up his own bait using molasses and bird seed. The idea is that rodents are always foraging for food. Bait is designed to attract the rodent to the trap - and thus exclude it from the house. Rats and mice eat just about anything. But the debate continues, as some professionals feel bait is unnecessary. It is true that placement of the trap - directly in the area where rodents are most likely to run - is critical. Baits don't always attract rodents, but they are useful in catching them once vermin encounter the trap. So the great bait debate goes on. For more information on rat and mouse control, try taking tomorrow's Rodent Quiz. See how you do, and check your answers on Wednesday. The more we know about what's bugging us, the more effective we will be.