GuideAbout

What’s happening outside now.

Look closerInsects

Bark beetle galleries: the patterns carved under loose bark

November to March

Lift a slab of loose bark off a dead log and the wood underneath often carries a branching pattern cut into the surface: one straighter tunnel with thinner tunnels fanning off it. The centre line is the gallery a female beetle chewed as she laid her eggs, and each branch is a mine cut by one larva feeding its way outward.

Why this time of year

The pattern is not seasonal; the beetles are long gone and the engraving just sits there in the dead wood. Winter is when it is easiest to find, because the forest floor is bare so dead trees and logs stand out, and dried wood sheds its bark more readily.

How to notice it

  1. Look for a dead standing tree or a fallen log where the bark is already loose, flaking or missing in patches. Do not pull at bark that is tight and green.
  2. Lift or peel a slab of the loose bark away by hand to expose the wood underneath.
  3. Look for a straighter central tunnel with thinner tunnels branching off it. Individual larval tunnels almost never intersect, which is why the fan stays readable.
  4. Compare a few logs. Some show that neat branching fan. Others show winding, crisscrossing tunnels, or a curving H or Y shape, which are still bark beetles but different species. Tiny round holes bored straight down into solid wood are a different insect altogether.

Try this with kids: Find the one straighter tunnel where the mother beetle laid her eggs, then count the smaller tunnels branching off it. Each branch was chewed by one grub eating its way outward.

gallery: a tunnel a beetle chews into wood. A larva is the wingless, grub-like stage before a beetle grows up

Safety

  • Only pull bark off wood that is already dead. Stripping bark from a living tree damages it and opens it to disease.
  • Standing dead trees can drop limbs or bark without warning. Give them space and work on fallen logs on the ground instead.
  • Wear gloves. Splinters, sharp bark edges and whatever is living underneath are all reasons.
  • Adult deer ticks are active in eastern Massachusetts on any winter day above freezing. Winter is not a tick-free season here; check afterwards as you would in summer.

Sources

  • northernwoodlands.orgNorthern Woodlands, presenting four native bark beetle species common in NORTHEASTERN forests. Verbatim: 'Individual larval feeding tunnels almost never intersect. In most species, larvae avoid competing for food by using olfactory, acoustic, and chemical cues to maintain distance from each other.' Gallery shapes verbatim: elm bark beetle, 'larval tunnels spreading out in a featherlike pattern from a central, straight-line tunnel where the female beetle laid her eggs'; eastern ash bark beetle, 'straight lines, perpendicular to the trunk, with larval tunnels extending off the sides'; Ips species 'typically create curving H- or Y-shaped galleries'; southern pine beetle tunnels 'take winding (often described as S-shaped), crisscrossing paths'
  • umass.eduUMass Extension. The female chews a tunnel 'at the interface of the inner bark and the outer wood' to lay eggs, and larvae hatch and feed by making galleries perpendicular to the female's gallery
  • bygl.osu.eduOhio State Extension. Ambrosia beetles bore through the bark and the phloem and straight into the xylem, rather than etching a pattern at the bark-wood interface. USED FOR CONTRAST ONLY
  • ipm.ucanr.eduUniversity of California ANR. Flatheaded borers (Buprestidae) and roundheaded borers (Cerambycidae) also mine under bark, and flatheaded borer galleries are 'flattened to oval in cross section, winding, and always packed tightly with frass'. USED FOR CONTRAST ONLY

Checked against these sources on September 15, 2026.

In the guide for November, December, January, February, March

Also worth noticing