A squirrel’s leafy tree nest, called a drey, looks like a scruffy clump of leaves from the ground. Inside, it is built in layers like a small insulated room. A soft, warm bed of plant fibres wraps around a hollow just big enough for the squirrel to curl up in. The lining works so well that, with a squirrel at home, the inside can sit around room temperature on a freezing day.1Wildlife Online. Squirrel Nests & Refugia
The Layers From Outside In
The outer shell is a woven frame. Squirrels bend green, still-flexible twigs into a ball where small branches meet.2Pott Conservation. What Does a Squirrel Nest Look Like Inside? The shell is made of twigs, leaves and sometimes vines, which form a strong outer layer for protection.3Skedaddle Humane Wildlife Control. Squirrel Nesting Habits4PubMed Central. Nest construction in mammals: a review of the patterns of construction and functional roles
Squirrels cut leafy twigs rather than gathering loose leaves, and that matters on the outside. The attached leaves overlap like shingles, which helps the shell shed rain and block wind. There is no glue and no nest cup. Green twigs are flexible when cut, and as they dry they stiffen into the shape they were bent into, so the ball sets into a rigid frame. Twigs are threaded through one another and wedged into the fork, so friction and tension do the work of an adhesive. A squirrel keeps adding and repairing, tucking loose ends back in, so a drey used for years is often tighter and denser than a new one.
Once the frame is up, squirrels pack it with layers of leaves and loose material such as vines, grass and bark.5Pott Conservation. What Does a Squirrel Nest Look Like Inside? Winter frames are interwoven with dry grass, moss and leaves.6Wildlife Online. Squirrel Nests & Refugia
The inner lining is many layers of soft material: moss, feathers, grass, leaves, shredded bark and pine needles.7Woodland Trust. Squirrel nests: how do they build them? Winter linings can include lichen and fur.8Wildlife Online. Squirrel Nests & Refugia
If you pulled a fallen drey apart, you would feel this gradient. The outside is coarse, with leaves still attached to twigs and often looking dead and brown. A few centimetres in, the material turns finer and more tightly packed. The centre is a soft, often shredded mass shaped into a hollow, and bits of fur or feathers may cling to the inner surface.
Not every leafy clump in a tree is a drey. Wind-blown leaves and tangles of dead leaves caught in branches can look similar from the ground, but a drey has a deliberate rounded shape wedged in a fork. Mistletoe and witches’ broom, which are dense clusters of twigs growing from the branch itself, are another common lookalike. Bird nests are usually open cups, while dreys are closed balls. Dreys are often easier to spot in winter, once the trees drop their leaves.
How Big the Chamber Is
A winter drey is typically about the size of a football, around 30 cm (12 in) across.9Wildlife Online. Squirrel Nests & Refugia The hollow inside is only about 6 to 8 inches wide, lined with extra shredded bark, grass and leaves.10Perky-Pet. All About Squirrel Nests Most of the ball’s bulk is wall and insulation, not living space. Gray squirrels can build bigger nests, with some inner spaces reaching 2 feet wide.11Perky-Pet. All About Squirrel Nests
A 6 to 8 inch hollow lets an adult curl up with its tail wrapped over its body, so the space fits a curled animal rather than a stretched-out one. It also leaves room to turn around, which helps because the squirrel enters and leaves through the same opening, a side gap in the woven wall that often faces the trunk. And because the hollow is only slightly larger than the animal, the squirrel’s body fills most of it, so its own heat warms a small pocket of air rather than a large room.
How the Inside Stays Warm
The squirrel is the heater. With the outside air at -5 °C (23 °F), a red squirrel’s drey held about 25 °C (77 °F).12Wildlife Online. Squirrel Nests & Refugia That warmth came from the squirrel’s own body heat after it went in.13Wildlife Online. Squirrel Nests & Refugia A drey has no heat source of its own, so it is not warm the moment a squirrel climbs in. After the squirrel re-entered, it took 10 to 30 minutes to warm back up to that steady level.14Wildlife Online. Squirrel Nests & Refugia When the squirrel left, the inside dropped to around 3 to 4 °C (38 °F) and never went below freezing.15Wildlife Online. Squirrel Nests & Refugia
The empty nest stays above freezing because the thick, packed lining holds on to warmth left behind, and the closed ball keeps wind from blowing through. The squirrel returns to a nest that is cold but not icy. A drey empty for a long time, though, ends up about as cold as the air around it, apart from some shelter from wind and rain.
Insulation works by trapping still air in small pockets between fibres, and it is the trapped air, not the material itself, that resists heat flow. Packed moss, shredded bark and grass hold many tiny pockets, which is why a springy, fluffy lining beats a thin, dense one. Damp material loses much of that ability, so a drey that sheds rain is also a drey that keeps the squirrel warm.
The savings are large. In flying squirrels, nest insulation cut a single squirrel’s heat loss by 37% compared with no nest.16Canadian Journal of Zoology. Winter energy expenditure and the distribution of southern flying squirrels Huddling in groups of 3 or 6 lowered their energy use by up to about 35% in the cold.17Southeastern Naturalist. Metabolic Benefits of Huddling during Acute Thermal Stress in Southern Flying Squirrels (Glaucomys volans) Sharing warmth and exposing less body surface is why squirrels in groups use less energy each than one alone.
Summer Nests vs Winter Nests
Summer nests tend to be shallow platforms of twigs.18Wildlife Online. Squirrel Nests & Refugia They are lighter, flatter and more open.19Ark Wildlife. Squirrel Nests: All You Need To Know Winter dreys are bulkier and more robust to protect against cold and harsh weather.20Ark Wildlife. Squirrel Nests: All You Need To Know
In warm weather the main problems are overheating and airflow, so an open, airy platform works better than a heavily lined ball. In winter the problem is heat loss, so the walls get thicker and the lining heavier.
Squirrels often keep more than one nest at a time. A light summer nest suits hot nights when insulation isn’t needed, and spare nests give a fallback if one is damaged or disturbed.
If you find a nest, a flat, see-through tangle is likely a summer platform, while a dense ball with soft lining is a winter or breeding drey. Many summer platforms fall apart within months. Nests don’t fall neatly into two types, though. A platform can be built up with more material as the weather cools, so an autumn nest may look partway between the two. A squirrel may also add to an old drey rather than start fresh, leaving a winter nest sitting on the remains of an older one.
Tree-Hole Nests and Other Species
Many squirrels also nest in tree holes, where the tree itself replaces the twig shell. Flying squirrels favour cavities more than leaf nests. In one Canadian forest, most northern flying squirrel and red squirrel cavity nests were made almost entirely of shredded cedar bark.21The Canadian Field-Naturalist. Cavity Nest Materials of Northern Flying Squirrels, Glaucomys sabrinus, and North American Red Squirrels, Tamiasciurus hudsonicus, in a Secondary Hardwood Forest of Southern Ontario Those nests averaged about 12 cm (5 in) deep, in spring and summer alike.22The Canadian Field-Naturalist. Cavity Nest Materials of Northern Flying Squirrels, Glaucomys sabrinus, and North American Red Squirrels, Tamiasciurus hudsonicus, in a Secondary Hardwood Forest of Southern Ontario
No woven outer layer is needed inside a hole. The walls of a cavity already shelter the animal from wind, rain and many predators, so the squirrel only needs to add a soft floor. Because the hole limits how much air surrounds the animal, less lining is needed than in an open drey, and the depth of the bark pad matters because it holds the squirrel off the cold wood.
Inside, the bark is stripped into long, thin fibres and packed down, so the pad feels fluffy and loosely felted rather than woven. The nest fills the shape of the hole, so it can be a flat pad in a wide hole or a deeper cup in a narrow one.
You may meet one in a birdhouse or attic. A box packed with shredded bark often means a squirrel, while bird nests in boxes are usually tidier cups of grass.
Who Else Lives Inside
A drey is a tiny ecosystem. In nests of one invasive squirrel species, every nest held small invertebrates, about 160 on average and up to 314.23BioInvasions Records. Organisms associated with nests of the invasive squirrel Callosciurus erythraeus (Pallas, 1779): an overlooked arboreal habitat for urban pests Flies were the most common, followed by springtails, mites and booklice.24BioInvasions Records. Organisms associated with nests of the invasive squirrel Callosciurus erythraeus (Pallas, 1779): an overlooked arboreal habitat for urban pests Some were potential household pests, including cockroaches and several kinds of flies.25BioInvasions Records. Organisms associated with nests of the invasive squirrel Callosciurus erythraeus (Pallas, 1779): an overlooked arboreal habitat for urban pests In Poland, 24 insect species were found living in red squirrel dreys.26Diversity. Target Species and Other Residents—An Experiment with Nest Boxes for Red Squirrels in Central Poland
A nest is a stable, sheltered, warm spot with steady food in the form of shed fur, skin flakes and droppings, so small animals can live and breed there. Some groups feed on the nest material, some on the squirrel’s waste, and some prey on other small creatures. Fleas and mites live on the squirrel and drop off into the bedding, where their numbers can build up. An old nest keeps hosting them after the squirrels leave.
Almost all of these creatures stay in the nest and are of no concern if you only see a drey in a tree. They matter when a nest is in or against a house, since some could move inside, as the cockroaches and flies in the findings suggest. Fleas from a squirrel nest can bite people, so they matter most when a nest has been disturbed and the squirrels have gone.
If you handle a fallen or removed nest, wear gloves, since nests can carry mites and fleas. Bag it before carrying it near the house, and wash your hands afterwards.
Plastic and Litter in Nests
Squirrels sometimes weave human litter such as plastic bags and paper into their nests.27Pott Conservation. What Does a Squirrel Nest Look Like Inside? In towns, Indian palm squirrels use plastic bags, plastic thread and cigarette butts alongside natural materials.28Down To Earth. Squirrels now use plastic to build their nests The more built-up the area, the more artificial material ends up in their nests.29Down To Earth. Squirrels now use plastic to build their nests In farm areas of Peru, single-use plastic bags were prominent in white-naped squirrel nests.30International Journal of Environmental Studies. White-naped squirrels use plastic waste for nest construction in agricultural areas of northern Peru
The choice is often practical. Litter is whatever soft material lies closest, plastic is waterproof and flexible like leaves, and scarce trees in cities leave fewer natural options.
Litter changes the nest. Plastic does not breathe or absorb water as leaves do, so a plastic-heavy nest can hold moisture. Thread, string and fishing line can wrap around a squirrel’s legs or neck, and young animals can become tangled.
In your own yard, you can pick up loose plastic, string and netting that squirrels could carry off. Leave natural leaf litter and bark for nest building, and avoid offering dryer lint or synthetic fluff.