Sapsucker holes and the wasps that follow them

Someone finds the trunk of a maple or a holly ringed with small holes, dozens of them, as straight as if they had been drilled with a jig. Sap weeps from the holes and wasps crawl on them. The first guess is usually borers, and the first worry is that the tree is dying. Almost always the culprit is a bird, the yellow-bellied sapsucker, and the tree is in no real danger.

What the bird is doing

The yellow-bellied sapsucker is a woodpecker a little smaller than a robin that feeds on sap rather than wood-boring grubs. It drills shallow holes through the bark into the living tissue, lets them fill, and returns through the day to lap the sap with a brush-tipped tongue. It also eats the insects the sap attracts.

Because the bird wants sap, its holes look like no other woodpecker’s: small, roughly a quarter inch across, shallow, and arranged in neat horizontal rows, often stacked into a band that runs partway or all the way around a trunk or along a big branch. In early spring the holes are round and a little deeper, reaching the sap rising in the wood. Once the tree has leafed out the bird switches to shallower, squarish wells that tap the sugary sap in the inner bark, and keeps them flowing by adding new rows above the old ones. It returns to the same trees year after year.

Birches, maples, hollies, apples, hemlocks and oaks are favorites in the East, but sapsuckers have been recorded on hundreds of species. The bird breeds across the northern states, into Canada and down the Appalachians at elevation, and winters across the South. So the tapping season depends on where you live: spring and summer in the North, fall through early spring in the South, and a few weeks each spring and fall along the migration route in between.

Who else feeds at the holes

A working sap well is a feeding station, and the sapsucker is only its first customer. Ruby-throated hummingbirds follow sapsuckers north in spring and drink at the wells before most flowers have opened. Other birds, squirrels and chipmunks visit them. In late summer and early fall, when few flowers are left, the wells fill with yellowjackets, hornets, paper wasps, flies and the butterflies that prefer sap to nectar: mourning cloaks, red admirals, question marks, commas and hackberry emperors.

None of these visitors is hurting the tree. The wasps are drinking at holes the bird made, and they disperse with the first hard frosts. Beside a door or a patio they are a nuisance for a few weeks; they are not a sign of anything wrong with the tree.

Does it hurt the tree?

Rarely. The holes are small and shallow, and an established tree walls them off and grows over them within a season or two. A big tree wearing a few bands of holes needs nothing from you.

The exception is repetition on a small stem. When a bird taps the same young trunk or branch heavily, year after year, the bands of holes can join into a ring of dead bark, and a ring is a girdle: everything above it starves. Young birches, thin-barked maples and mountain ash suffer most, and on thin-barked species the wounds can occasionally admit canker or decay fungi. A small, valuable tree that a sapsucker has adopted is worth watching; a mature one is not.

What not to do, and the little you can do

• Do not paint, tar or seal the holes. Wound dressings do nothing for a tree, which walls off damage rather than healing it the way skin does, and they can trap moisture against the wound.
• Do not smear sticky repellents on the bark. They injure it, are hard to remove and rarely stop the bird.
• On a small tree that matters to you, during the weeks the bird is active, wrap the tapped section loosely in burlap or stand a cylinder of hardware cloth an inch or two off the bark. Move it if the bird moves, and take it off once the bird has gone so it does not hold moisture or girdle the stem. The same hardware cloth does double duty against rabbits and voles in winter.
• Consider leaving a favorite tree to the bird. Sapsuckers concentrate on one or two trees, and a big maple tapped for years is drawing the bird away from everything else you planted.
• Do not trap, shoot or harass the bird. Sapsuckers, like every native woodpecker, are protected under federal migratory bird law, and harming them or their nests without a permit is an offense.

Sapsucker, borer or woodpecker?

Three kinds of holes get confused, and they mean different things.

• Sapsucker. Small, uniform, shallow holes in tidy rows and columns, on live bark, often in bands around the stem. Fresh ones weep sap. No sawdust.
• Borers. Holes scattered at random rather than in rows, because they are exit holes made by adult insects leaving the tree. Round or D-shaped depending on the insect, often with sawdust-like frass or dried sap at the opening, usually on a tree that was already stressed. Frass in bark crevices or at the base of a tree points to borers, and borers are worth taking seriously.
• Woodpecker feeding excavations. Large, irregular, ragged holes or deep rectangular trenches, with chips on the ground, in dead or dying wood where the bird is digging for carpenter ants or beetle larvae. The woodpecker is not causing the decay; it found insects in wood that was already dead.

Rows mean a sapsucker, and the tree will almost certainly be fine. Random holes with frass mean borers; get the tree looked at. Big excavations mean the question is the dead wood, not the bird.