38 



called Ambrosia, which grows in a dense glistening layer upon the walls of the 

 tunnels and cradles. It penetrates the cut wood-cells and grows for a con- 

 siderable distance along the vessels; but is entirely saprophytic in its relations 

 to the wood. The walls of the tunnels are stained black for a millimeter or 

 more in thickness. These small, black, round, branching tunnels in the wood 

 are characteristic of the Timber-beetles or Ambrosia-beetles. 



The winter is passed by parent adults in the tunnels, young adults in the 

 tunnels and cradles, and pupse and larvae of various sizes in the cradles. Ap- 

 parently work is continued in these tunnels in the spring; and new tunnels 

 are started by the young adults. A second brood appears and starts fresh 

 tunnels early in August. 



The Pacific Coast Timber-beetle, an undescribed species of the genus 

 Platypus, is abundant on the coast and island in the same trees with G. sulcatus, 



Fig. 21. The Pacific Coast Timber-beetle; 



Platypus undes. sp.; female; 

 greatly enlarged. (Original). 



and G. retusus. Its habits are quite similar to those of Gnathotrichus, except 

 that the eggs are deposited free in the tunnels, and not in special niches. The 

 tunnels are slightly but distinctly larger than those of Gnathoirichus, and pene- 

 trate the trunk for from six to ten inches, giving off lateral branches. The 

 entrance-tunnel often enters four or six inches before any branching occurs. 

 There is probably one brood in British Columbia. Tunnels which were started 

 in August and September contain parent adults and eggs during winter; and 

 are completed in the following season. 



