It’s sugaring season, and the sweet bounty of spring is flowing. In sugarbushes all over the Northeast people are busy collecting the sap of sugar maples and processing it into maple syrup and other maple products. But we aren’t the only ones harvesting tree sap. Squirrels are also busy tapping trees, and the sugary nourishment makes an important addition to their spring diet.
You’ll find squirrel taps like the ones in the photo below on thin-barked branches or small trees. Black birch–pictured in the photo–and sugar maple are the most commonly tapped trees in the northeast, but they’re not the only ones. Sap containing sugars and other nutrients flows in all trees in late winter and spring when conditions are right. Sue Morse has documented squirrel taps on 23 different tree species.
To make a tap a squirrel turns its head sideways and uses its incisors to bite into the bark deep enough to penetrate the outer layers of sapwood. Sometimes, as in the photo below of a squirrel tap on a sugar maple, the resulting gouges make a dot-dash pattern. The dot is the spot where the upper incisors were anchored, and the dash is the cut made by the lower incisors as they were drawn toward the upper ones.
Both red and gray squirrels (and possibly also flying squirrels) make sap taps. Red and gray squirrels have been observed moving around in trees making numerous bites in rapid succession. But instead of licking the sap immediately they use a more efficient method, waiting until the water has evaporated and then returning to consume the crystallized maple sugar.
The squirrel tap on black birch in the next photo may have started as a simple dot-dash pattern, but it didn’t stay that way. It looks like the squirrel kept biting at it to make an irregular wound. The green surfaces are the cambium, the thin layer of living cells that produce wood and bark during the growing season. Just beneath the cambium is the wood formed in the previous summer. Its xylem cells are no longer alive, but they are connected end-to-end to form long tubes, and this is where most of the sap flow is located. Depending on the conditions, sap may also flow in the phloem cells of the most recently formed bark, located just outside the cambium. Once exposed, cambium tissue rapidly dies and turns brown, so I must have come upon this tap very soon after it was made. In the lower part of the photo you can see some dark brown bites that were made earlier in the same season.
Stems that are heavily tapped can take on a ragged appearance, as in the next photo of taps on black birch.
Once the growing season begins the tree attempts to heal the wounds. Cambium cells proliferate around the edges of the bared wood, and new callus tissue grows inwards. Small cuts may be covered in the first summer, but larger scrapes take longer. Tapping over several years can result in trees and branches covered with numerous callused scars, like those in the photo below of black birch.
So how does one find squirrel taps? Vigorous trees with plenty of exposure to the sun are preferred by the furry harvesters because they produce sap with high concentrations of sugars. Since most taps on large trees are too high for us to see from the ground, we’re limited to small trees or larger ones that have suitably low branches. But even if we find a big, healthy sugar maple with low branches it may not have any taps, because squirrels are choosey about the trees they tap. Individual trees may taste different because their chemical profiles aren’t exactly the same. Fortunately, wounds created by squirrel taps persist for months or even years, so if you locate a promising tree you may find evidence of sweet-toothed squirrels long after sugaring season is over.