An unusual smell coming from a tree trunk puzzles many gardeners. The reason is deep in the wood.
All of a sudden there is a strong smell of vinegar in the garden, right next to the tree, and for no obvious reason. The culprit is hiding in the wood: the caterpillar of the goat moth, up to four inches long and as thick as a finger, with a striking red and yellow color. Week after week it eats its way through the trunk.
Goat moth: these signs give away the tree pest
People who notice the smell will often find the second clue right on the trunk, which is big round holes in the bark. The culprit is probably the goat moth, a night moth from the family of the wood-boring moths, the Chamber of Agriculture of Lower Saxony says. The moth itself is rarely seen, its gray, mottled wings give it perfect camouflage on the bark.
Most of the time you only see the infestation through the caterpillar, and the caterpillar is easy to identify. The back is dark red, the underside has a yellow shine and the body, according to the gardening site Mein schöner Garten, looks shiny like it was lacquered. You should still handle it carefully though. It is not poisonous, but it can bite hard.
Why goat moth infestations often go unnoticed for years
A lot of gardeners are surprised by the vinegar smell, but the infestation usually started years before that. The females lay up to 700 eggs in cracks in the bark of trees that are already weak. When the young caterpillars hatch they first eat through the bark as a group, and after that each one goes deeper in on its own, so nobody sees them anymore.
That can take two to four years, says the Chamber of Agriculture, and the caterpillar eats tunnels in the wood that are up to three feet (one meter) long during that time. Mein schöner Garten says the vinegar smell and fine reddish wood shavings at the bottom of the trunk are signs of what is happening inside the tree. Ignore them and the infestation can go on for years and nobody notices.
When the goat moth puts the tree at risk of breaking
If nobody notices the infestation for a long time, the tree is in more and more danger. The more tunnels there are, the less stable the wood is, and then wind and snow break branches more easily, the Chamber of Agriculture of Lower Saxony warns. The old and weak trees in a garden are the ones most at risk, because the goat moth prefers to lay its eggs there.
On top of that, fungi that rot wood spread more easily through the feeding tunnels, and they make the trunk even weaker from the inside, according to the Chamber of Agriculture of Lower Saxony. In the worst case the whole tree dies.
Photo: Alfried h.
