There are several species of squirrel, but tree squirrels are the most common nuisance for homeowners because they inhabit attics and garages and cause damage. They often gnaw on the exterior and interior walls, timbers, cables, and electric wiring. They have been known to short out electric power transformers due to their activities around power lines. Squirrels are typically discovered because they make a lot of noise in the area they inhabit. The gray squirrel is the most common structure-infesting squirrel species.

Squirrels are abundant in the wild because their numbers far exceed the number of predators. The large population and decreasing natural habitat due to construction in many areas cause them to seek shelter in houses. The chilly months of fall and winter cause squirrels to seek the warmth that is found in attics.

What can I do to keep squirrels out of the attic or garages ?

Answer: A consistent trapping program is best for squirrel control.

Squirrel Control Recommendations

• Removal of any diet source: bird seed for example, because they attract the squirrels is the first order of business.
• Using gutter guards and covering downspouts will reduce the number of squirrels that are entering through the rooftop and facia boards. 
• There are no poison baits on the market that squirrels will eat and die, except Ditrac Ground Squirrel Bait that is only made to control the California Ground Squirrel (found in western states). Typical rodent control bait for mice and rat control will not work against other squirrels.
• Live trapping method of trapping squirrels is the only way to remove unwanted squirrels. Catching a squirrel is really the only way to get rid of squirrels in your attic, once they have chewed holes. It is important to seal up and repair all entry points after trapping the squirrels, so they no longer have access.
  1. Locate the trap along the path of entry and places of known foraging activity. 
  2. Go about 4-5 miles away to relocate the squirrels, or it will find its way back to your area. 
  3. You may want to consider local ordinances for trapping squirrels, in that they differ. Sometimes a professional trapper with a nuisance control license is needed to not only capture the squirrel but relocate it as well. 

How to prevent squirrel entry to buildings

• Trim tree branches that may overhang the roof line.
• Remove firewood stacked against the building.
• If there are cracks in the foundational wall, repair them.
• Seal entry points

Trapping Tips

• Always use work gloves when handling the traps with a squirrel inside. 
• Some trappers like to use a technique called "pre-baiting" to gain the squirrel's confidence. Leave the trap out, wired open (so it won't shut) with the bait so that they can get used to the object in their environment. However, most of the time this technique is not needed to trap squirrels successfully. 
• Place traps where you hear or see the activity. Using a Rat/Squirrel lure (walnut/nut oil based) on a cracker or piece of fruit behind the trip pan is very helpful as a lure. You may also try peanut butter. Next use sunflower seeds on top of that and trail a line of sunflower seeds out the front door of the trap so that there are "free" seeds a couple of feet in front of the trap. This will help overcome any anxiety the squirrels may have about entering the trap.

Trapping Gray Squirrels-Use 1 inch or 1/2 Grid Traps:
For trapping gray squirrels,you will want to place their traps along with their pathways or points of entry, such as along the roof, at the base of a tree, or base of the building they are entering.

Trapping Flying Squirrels-Use 1/2 Grid Traps:
Flying squirrels would need to be trapped inside the attic areas because they glide into the attics. Look for their areas of activity, such as droppings, when placing the traps. Also look into insulated areas that they use for nesting to place traps.

Exclusion and Relocation of Squirrels

After trapping and relocating the squirrels you can seal the openings with 1/4" mesh hardware cloth or metal flashing. Look for all possible entry points. If you are not handy with tools, many wildlife control companies will seal entry points with a year's guarantee. 

Squirrel Exclusion Products

There are several exclusion product that we recommend. Use a copper mesh wool or Xcluder Fill Fabric to stuff into holes and bigger openings. For smaller openings, use Foams in an aerosol form such as Pur Black NF Foam. It fills and seals voids.

Squirrel Repellents

Using Bobbex-R Animal Repellent repels Squirrels and other small animals (chipmunks, groundhogs, and voles). It repels them by taste and smell aversion. It is made of natural ingredients and benefits plants as well. It comes in a ready-to-use formula and concentrated formula.

Flying squirrels

he typical habitat for the Flying Squirrel is inside tree cavities in hardwoods. Smaller than the gray squirrel, they enter the tiniest of cracks and holes. The flying squirrels are about 9 inches long, which includes a 3-4 inch tail and weigh about 3 ounces as an adult. They have a dense, soft brown fur, white belly. The flying squirrels don't really fly but glide into attics from trees. They glide using a thin skin that extends out from the sides of the body and connects the front and hind legs as shown in the above picture. In "flying," the squirrels leap spread-eagled and use their outstretched gliding membranes for gliding and their bushy tails for guidance. Glides of 60 meters (almost 200 feet) or more have been recorded of the Flying Squirrels

Fly squirrels are nocturnal with their major activity at night. They are known to make plenty of noise during the night. Can by commonly heard, making a great deal of noise at night between sunset and sunrise. They may be heard landing on the roof or the sides of the house.

How Flying Squirrels Enter Buildings 

Flying Squirrels can enter the attics through the eaves and soffits thru small cracks. These squirrels may easily enter the space between the roof top and facia board, chewing the area for a wider entry point.

Gray Squirrels

Gray Squirrels are about 18 inches long, including their 9-inch tails. They are larger than the flying squirrels. Gray Squirrels weigh about 1-1.5 lbs. as an adult. Their coloration is usually gray, salt and pepper, but can have tan hairs in the fur as well with white bellies. The winter coat is grey above with a white underside; the summer coat is shorter, sleeker and brownish grey above. Red squirrels have red/brown upper parts in summer but may show some grey on the back in winter, leading to some confusion. Red squirrels are smaller, lighter, have ear tufts, prominent in the winter coat and brown on the legs and tail.

Natural habitats for Gray Squirrels are wooded areas in tree cavities, and they can be found near hardwoods like oaks and hickory trees. These squirrels will construct feeding shelters out of leafs.

More Gray Squirrel Features

• Generally have 2 litters a year, 2-4 young per litter. They normally breed in midwinter and late spring. Gestation is about 44 days.
• Diet consists of bird eggs, insects, berries, fruit, vegetables, nuts, and nestling birds. They like to hoard their food.
• Gray squirrels are active during the day, expecting to hear them during the daytime.
• Can inhabit the attic areas as well as crawl spaces. They like to enter the attic areas from your gutters and nearby trees and bushes. Installing gutter guards, or downspouts with the screen may prevent them from climbing up to the roof through a downspout.

Red Squirrel

The American red squirrel is smaller than the flying or gray squirrel. It has a deep red color with a whitish underbelly and a distinctive white ring around its eyes. Their tails are not as bushy as other tree squirrels, and the color varies from red-brown to yellow-gray. They measure about 6 inches with a tail length of about 3-6 inches. Sometimes Red squirrels and Gray squirrels can look similar, even with their color variations. Red squirrels have ear tufts, while gray squirrels do not have ear tufts.

The Red squirrel has a notable screech, chirp or growl, they are very vocal. They range across USA and Canada, from the Rocky to the Appalachian mountains and from Arizona to Georgia. They are active during the day and feed on nuts, seeds, conifer cones, but will also feed on fruits, birds'eggs, and nestling birds. They will defend their territories more so than other squirrels. They do not hibernate but will seek shelter during adverse weather conditions. Just before winter, they hoard food in nests, burrows and tree cavities. They mate during the spring months and fall months.

Thirteen-Lined Ground Squirrels (Striped gophers)

The thirteen-lined squirrel is a another common pest found around lawns and foundations. They prefer grassy areas and hibernate during the winter months. They can damage newly planted seed, and pull up wheat, oats, and barley. They eat mice and insects. They make burrows, but are poor climbers. They are commonly distributed among the midwest, from northern Texas to parts of Canada.

Source: https://www.doyourownpestcontrol.com/squirrelcontrol.htm