52 
her eggs in the smaller twigs of living trees, most commonly in 
July. The young larva first eats out the wood under the bark in 
the direction of the grain, packing its burrow behind it with its 
castings, and working towards the base of the twig. Later it cuts 
holes in the bark thru which these castings are rejected, and 
then follows the center of the twig, making a channel more or less 
oval in cross-section, corresponding to its own shape. When it has 
reached its growth it begins to gnaw, from within, a circular groove, 
deepening this until the twig or branch is so weakened at this 
Pig. 57. Oak Twig-pruner, Elaphidion villosum, 
adult. About 5 times natural size. 
point that the wind readily breaks it off, usually carrying the insect 
with it. Occasionally, however, the larva is left in its burrow on 
the tree and finishes its transformations there. The value of 
this operation to the pruner would seem to be a preparation for 
the exit of the l)eetle, which originates within the burrow, but 
which has not jaws of a sufficient strength to enable it to gnaw 
its way out thru the wood inclosing it. This explanation, given 
by Chittenden, seems at least to be the most reasonable among 
several that have been proposed to account for this curious habit. 
After the twig has been cut off the larva within it plugs up the 
severed end, changes to the pupa, and later to the beetle, coming out 
as an adult the following summer. 
