Large elm beetle larval galleries. Large elm beetle (Scolytus scolytus) larval galleries in the lower surface of elm tree (Ulmus sp.) bark. The female beetle burrows into the bark creating long narrow chambers. At regular intervals she makes a small niche into which she lays an egg. When the larvae hatch they feed on the bark, moving away at right angles from the chambers formed by the adult. Large elm beetles were the vector for the fungus that caused Dutch elm disease, which decimated British elm trees in the early 1970s.