Squirrels, Ahoy!

What It Covers

Stuff You Should Know hosts Josh and Chuck explore squirrels across nearly 300 species, covering their evolutionary history spanning 35 million years, three behavioral categories (ground, tree, flying), their near-extinction in urban America, reintroduction through city parks, and the ecological role they play as forest gardeners.

Key Questions Answered

• •Squirrel taxonomy: Squirrels divide into three practical groups — ground squirrels (which include prairie dogs, chipmunks, marmots, and groundhogs), arboreal tree squirrels, and nocturnal flying squirrels. Flying squirrels are as common as tree squirrels in many regions but appear rare because they operate exclusively at night, gliding up to 300 feet using a skin membrane called a patagium.
• •Ecological role as forest gardeners: Tree squirrels bury food across territories up to 25 acres, using scent glands on their feet to mark retrieval paths. When they forget buried nuts — which are technically seeds — those nuts germinate into new trees. This scatter-hoarding behavior actively expands and regenerates forest ranges, making squirrels a primary driver of woodland growth.
• •Urban squirrel reintroduction: Eastern gray squirrels were nearly eliminated from American cities by the mid-1800s through hunting and pest control. Philadelphia and Boston began deliberate reintroduction programs, followed by Frederick Law Olmsted's large urban park movement. Feeding squirrels was then framed as a moral-education tool for children, fundamentally reshaping public perception from vermin to beloved urban wildlife.
• •Road-crossing behavior explained: When squirrels freeze or dart erratically in front of vehicles, they are executing an evolved predator-evasion strategy — freezing to assess a threat's direction, then juking the opposite way. This works against hawks and foxes but fails against cars traveling in straight lines. Slowing down gradually rather than braking sharply gives squirrels time to complete their instinctive escape pattern.
• •Feeding squirrels correctly: Optimal squirrel foods are unshelled mast nuts — walnuts, chestnuts, acorns, hazelnuts, and pecans — which also grind down their continuously growing incisors. Avoid raw peanuts, which carry aflatoxin, a fungal compound toxic to both squirrels and humans. Shredding fruits and vegetables prevents squirrels from burying produce elsewhere in gardens. Overfeeding triggers population booms and potential attic colonization.