Nearly everyone can name a holiday after the groundhog. Far fewer have watched one long enough to recognise what it actually spends its year doing.

The groundhog — also called a woodchuck, or less formally a whistle-pig — is the largest member of the squirrel family found in New Jersey. Beyond the Groundhog Day folklore, it is an accomplished digger and one of the few local mammals that truly hibernates, spending most of its life either underground or within a short dash of a burrow entrance.

What they look like

Groundhogs are stocky and compact, typically 16 to 20 inches long and weighing 5 to 10 pounds, with a short bushy tail adding another 4 to 7 inches. Their fur is a grizzled brownish-gray with a frosted look, the effect of lighter-tipped guard hairs lying over a dense undercoat. Short, powerful legs end in long curved claws built for digging. A curved spine and low-slung build give them a silhouette quite unlike a tree squirrel’s — closer to a small furry bulldozer than to anything that belongs in a tree.

Family life

Groundhogs do not pair up in any lasting way. Males emerge briefly from hibernation in February to establish territory and visit females at their burrows — a short pre-mating period that lets breeding happen quickly once both sexes fully emerge in March. A male will typically mate with more than one female in his territory before moving on; females mate with only one male per season.

After a gestation of about a month, females give birth to a litter of two to six kits, usually between April and early June, timed so the young have enough of the growing season left to fatten up before their first hibernation. Kits are born blind and hairless and nurse in the burrow for about six weeks before starting to forage on their own. They stay with their mother for a few months, sometimes foraging together as a loose family group, before dispersing to dig burrows of their own — often taking over an old abandoned one rather than starting from scratch.

Daily habits

Groundhogs are active during the day, especially in early morning and late afternoon, and spend much of that time foraging or basking in the sun near a burrow entrance. The alert, upright posture they strike while surveying their surroundings is one of their most recognisable behaviours.

They are mostly herbivores, favouring clover and other tender greens in spring and moving on to garden vegetables, fruit and field crops later in the season — the root of most groundhog-versus-gardener conflict. Despite their bulk they are capable climbers and swimmers when they need to escape a threat, though their first instinct is almost always to retreat underground.

A true hibernator

Groundhogs are one of the few New Jersey mammals that genuinely hibernate rather than simply slowing down for winter. They enter a deep, energy-saving state each autumn in which heart rate drops from a normal 80 to 100 beats per minute to just four or five. They typically go dormant in October or November and lose 30 to 40 percent of their body weight by the time they reemerge, gaunt and hungry, in late February or March.

Territory and range

A groundhog’s burrow is a serious piece of engineering: a main system can run more than 30 feet, with multiple chambers and several entrances including hidden escape exits. Groundhogs favour the edges of woods next to open fields, lawns or gardens, and a single animal will often maintain more than one burrow across its territory — a main den for raising young and hibernating, and smaller satellite burrows used for feeding or quick escape elsewhere on its range.

A persistent myth: aggression and rabies

Groundhogs have a flight response as their default reaction to a threat and are not naturally aggressive toward people. Cornering one, or approaching a den with young present, is the main way an encounter turns confrontational. Like any mammal they can contract rabies, and the genuine warning signs are the same as with other wildlife: daytime disorientation, stumbling, unprovoked aggression, or a total loss of fear around people or pets. A groundhog simply going about its business — foraging, sunning, retreating into its burrow when approached — is not a cause for concern.

Keeping them out of the garden

Groundhogs can eat well over a pound of vegetation a day, so a garden inside their territory tends to get noticed quickly. There are effective, humane ways to make a garden unappealing without trapping or removal — and they work better than removal does, because a vacant burrow in good habitat simply attracts the next groundhog.

• Fencing is the single most reliable method. Use heavy poultry wire or 2-inch woven mesh at least 3 feet above ground, buried at least 12 inches deep, with the bottom 6 inches bent outward in an L-shape to stop digging underneath. Angling the top 10 to 15 inches outward at 45 degrees also discourages climbing over.
• Remove cover and food sources nearby. Groundhogs den close to their food, so clearing brush piles, trimming low shrub branches and picking ripe or fallen produce promptly all make a yard less appealing to begin with.
• Try scent and taste deterrents, refreshed often. Products containing castor oil or capsaicin, or a homemade cayenne pepper spray on foliage, can help. These wash away in rain and need reapplying every week or two to stay effective.
• Add motion-based scares. Motion-activated sprinklers, wind chimes or mylar balloons near a burrow entrance take advantage of how skittish groundhogs naturally are, sending them straight back underground at the first surprise.
• Consider dense and companion planting. Groundhogs tend to avoid strongly aromatic plants like lavender, chives and marigold — worth planting as a border for beds that are otherwise a groundhog favourite.
• Layer methods together rather than relying on one. Fencing plus habitat modification plus a rotating scent deterrent is consistently more effective than any single approach, since groundhogs are persistent and will test a garden’s defences repeatedly.

Planning a yard that works for wildlife rather than against it? See our guide to designing your yard for coexistence.

Living alongside groundhogs

• Protect vulnerable beds rather than the whole yard. A well-anchored fence buried a few inches into the ground is the most reliable way to keep groundhogs out of vegetables without conflict — they are diggers, not just climbers.
• Check under sheds and decks before sealing gaps. These are common den sites. Confirming no groundhog is present — especially a nursing female with kits below — avoids sealing an animal in.
• Time exclusion work outside the spring denning season. Late summer and autumn, after young have dispersed, is the least disruptive window to close off an unwanted burrow entrance.
• Recognise burrow damage for what it is. Undermined soil near a foundation or shed is worth addressing, but it is a structural issue to manage, not a sign the groundhog means any harm.
• Give them space, especially near a den. A groundhog that feels cornered is far more likely to act defensively than one given a clear path to retreat.

An unassuming, mostly solitary digger, the groundhog spends the bulk of its year quietly doing the two things it is best built for: eating enough to survive a long winter, and building the burrows that go on to shelter plenty of other wildlife long after it has moved on.

What neighbours have tried

• “I use charcoal briquettes in foil pans covered with shaved-down Irish Spring soap. Mice hate the smell, so do other animals like deer and snakes.”
• “I poured a little vinegar down the entrance (they dislike the smell), placed obstacles in his path, and sprinkled cayenne pepper around the burrow. Eventually he decided to move — just to the other side of my yard! I repeated the process, and before long he found himself a new residence elsewhere.”