After some preliminary research I quickly realized what type of species I was starting to investigate; species within the realm of wood-borers, or species which eat and destroy wood (Xylophagous species, from Greek "xylon" for wood and "phagus" for eater). These species range considerably in their characteristics (as well as richness, with over 10,000 species of wood-boring insects identified).
- All make unique patterns or “galleries” where they live and lay their larvae,
- all produce and leave behind unique types of frass (excrement from eating wood),
- all prefer different species of wood to bore into,
- and all prefer different levels of health in the tree's which they choose to bore into.
After realizing the tree I was leaning against was once home to massive borer community, I looked around the area (a stand of conifers, mostly white pine and hemlock) and was surprised to find that most of the downed trees in the area had once been host to this same borer species. After researching with Eiseman and Charney's Tracks and Sign of Insects and many hours of poring over internet databases, I was unable to come to a conclusion on exactly what species of borer did this, however I did come to the conclusion that it was some sort of bark beetle of the Curculiondae family within the sub-family Scolytinae (linked at the bottom of this posting is an official Vermont State report on insects which likely contains the correct species). These beetles feed on the cambium layer of trees, creating distinguishable patterns in the inner bark and outer sapwood. It is unlike bark beetles to bore deeper than 3mm into the sapwood layer of the tree, which matches what I observed in my tree. Most commonly, bark beetles will attack a tree that is already injured or diseased, often killing it in the process.
The most basic bark beetle gallery begins with the creation of a mating chamber, from which a female excavates a linear tunnel of uniform width either perpendicular or parallel with the grain of the tree (mine went parallel). On either side of the tunnel, the female creates small little niches and lays an egg in each one. I was able to see these niches in my downed tree species (these were in white pine, Pinus strobus); they look like tick marks that are evenly spread out following the main tunnel (see image above).
Wood borers serve the ecologically keystone task of facilitating tree decomposition by creating holes and channels in the woody tissue, phloem, and bark of the stressed, diseased, or dying trees which they feed on. This allows for fungi to enter the tree and begin decomposition.