Two species of beetles (Scolytus multistriatus or Hylurgopinus rufipes) create tunnels under the bark of Elm trees as they feed and lay eggs behind them. Their larvae create tunnels at right angles to the main tunnel. The resulting pattern is called a gallery. The beetles and their larvae carry the fungal spores of Dutch Elm Disease pathogens (Ophiostoma ulmi and Ophiostoma novo-ulmi) to new trees.