I've been working on that trail obstruction, and I found some nice bark beetle galleries to show you. This tree does happen to be an Elm, and it was bark beetles that carried the Dutch Elm Disease that pretty much wiped out the American Elm, but the beetles themselves were not the problem, and these galleries tell me that it wasn't even made by the disease-carrying beetle.
Not all galleries are patterned, some are just twisted passageways like the picture above. You can find these tunnels under the bark of many dead or dying trees, not just elms. I learned a lot, checking this out to write about. European elm bark beetles have the main egg laying chamber running with the wood grain, and side larval tunnels running across the grain, like these pictures. The native elm bark beetle builds its chambers at 90 degrees from this, and the native beetles are the ones that carry the disease. The European beetle is smaller.
For the most part, bark beetles simply help break down dead or dying wood. But they get a lot of notoriety when there is an outbreak of some disease-carrying kind that infects a large number of trees. I've included a link to more info below.
|See Univeristy of Minnesota Extension about bark beetles
See Monthly Winners for the dead wood where I found these