Bark Stripping by Fox, Gray, Red, and Ground Squirrels
Identification and Causes
Damage to Tree Bark
Fox squirrel (Sciurus niger) and gray squirrel (Sciurus carolinensis) damage to tree bark (called bark stripping) can be quite severe. See photo at right by Dallas Virchow.
A gentleman in Pennsylvania reported that red squirrels (Tamiasciurus hudsonicus) also strip bark.
Identification of Bark Stripping
- Fox squirrels live in the middle portion of the continental U.S. (The range of gray and fox squirrels overlap).
- Gray squirrels live in the Eastern portion of the continental U.S.
- Typically, strippings are 1/2 inch wide and 3 to 6 inches long. Other small limbs and branches of 1 to 2 feet in length and 1/4 to 1/2 inches in diameter are clipped and dropped to the ground.
- Squirrels prefer to strip horizontal branches, but have been known to strip trunks too. Damage can be extensive.
- Red squirrels like to clip branches of maples (particularly sugar maples) to get the sweet sap.
- Bark stripping usually occurs in late winter, but it can occur in the spring if trees don’t produce mast (acorns, pine seeds, maple seeds, etc.).
- Incisor widths–These figures encompass the range in the width of teeth between upper and lower incisors and between male and female squirrels.
- Gray squirrel (Eastern)–1.17 to 1.74mm
- Gray squirrel (Western)–1.19 to 2.25mm
- Fox Squirrel (Eastern)– 1.40 to 2.30mm
- Red Squirrel
Types of Trees Stripped
- Ash (Boise, ID)
- Atlas Cedar (ID)
- Autumn Olives (NE)
- Bald Cyprus (Cleveland, OH, 2013)
- Cedar, (Tacoma, WA, Sept 7-21, 2013) western gray
- Cedar, Washington Red (WA June, 2010; Puyallup, WA Nov 2013) western gray squirrel
- Corkscrew Willow (OR) December, 2008
- Elm (San Mateo, CA) May, 2009 Damaged branched up to 2-inches in diameter; Austin TX 2009-2012.
- Elm (Visilia CA; 2010) ground squirrel stripped 2 branches
- Ginkos (TX)
- Gingko Biloba (Visilia, CA; 2010) ground squirrels
- Globe Willow (ID)
- Hackberry (NE)
- Honeysuckle (NH) (Gray Squirrel) Winter 2008/9
- Honey Locust (NE)
- Japenese Maple (OR Dec, 08; Cupertino, CA July, 10).
- Lilac Bushes (Jan, 2010; Syracuse, NY May, 2014).
- Linden–Small Leaf (Ontario, Canada, stripped in Mid-November, 2008; Rochester, NY; March, 2010. New Hampshire; All year)
- Locust Trees (red squirrels Kansas July, 11)
- Maple (FL, MN, NE July, 09; stripped 2 ft sections of trunk, Austin, TX, May, 2012)
- Maple, Japanese (TX)
- Maple, Large Leaf (OR/WA, 2010)
- Maple, Red (NE)
- Maple, Sugar (MN)
- Maple, Vine (WA, June, 2010) Western Gray Squirrel
- Mulberry Tree (fruitless, OK May/June 2009; water available- Vallejo, CA July, 2011; water available; fruitless-Carrollton, TX May, 2014 )
- Oaks–various varieties (TX; NH May, 2010)
- Pin Oak
- Live Oak (DFW Airport, TX, June, 2009; Austin, TX, May, 2012)
- Red Oak (25 year old red oak; Stripping has occurred mostly in the crooks of the limbs where they meet the trunk. San Antonio TX. June, 2010.
- Pecan (GA June, 2009)
- Pines–various varieties (Southern GA, July 2011)
- Loblolly (Southern GA July, 2011;)
- Longleaf? (Southern GA July, 2011;)
- Slash (Southern GA July, 2011;)
- Poplar (GA)
- Poplar (Tulip Variety; OH, Spring, 2013)
- Red Wood (Northern CA April, 2011)
- Russian Olive (Milton, Ontario)
- Siberian Elm (Denver, CO, June, 2013)
- Sycamore (NE)
- Willow, Globe
Why Squirrels Strip Bark
There are several theories.
- Pregnant females often don’t eat just prior to giving birth. Bark stripping may be their way of responding to the pain.
- Searching for water (although this theory has been weakened by observing that squirrels strip bark even during a wet spring).
- Searching for food by eating the inner bark layer. Remember, just because a squirrel has access to a quantity of food, doesn’t mean it is obtaining sufficient nutrients.
- Squirrels may strip bark simply because they enjoy doing it, just as some people enjoy doing less than ordinary activities.
- We may never have a complete understanding of why bark-stripping occurs.
Squirrels also damage trees by limb/twig cuttings
- Timing: Typically occurs in spring (nest construction) and fall (crop gathering). Pin oaks seem to be typically hard hit (Source: Jerry Pickel of PA).
- Tassel-eared squirrels feed on twigs for the nutrients found in the cambium and subcambium layers of pine and firs (Source: Richard Wadleigh).