CARPENTERS AND WOOD-WORKERS 115 



would be filled by the descending sap and the grubs 

 would be drowned by it. 



There are two things in connection with Scolytus 

 that should be reverted to. It has sometimes been 

 stated that the side burrows starting off at right 

 angles from the central boring is due to a remark- 

 able instinct which leads the insects to this course 

 in order that they shall avoid breaking into or 

 crossing those of their brethren. Instinct has 

 nothing whatever to do with it ; it is a case of 

 " Hobson's choice." Any one who has stripped off 

 bark from an attacked elm knows that all these 

 burrows are closely packed with powdered bark 

 that has passed through the digestive organs of the 

 insects. If the newly hatched grubs did not turn 

 their attention to the sound bark before them they 

 would have to feed upon this excrement. 



Another statement we have seen made is that 

 the larvae never break into neighbouring burrows. 

 As a rule they do not ; but we have met with many 

 cases in which they have done so, and we have 

 seen examples in which one set of burrows have 

 gone right across another set at right angles. 



There are other beetles allied to Scolytus that 

 attack the bark of trees. Two of them — 5. rugulosus 

 and S. pruni — belong to the same genus and attack 

 plum-trees in a similar way. Hylesinus fraxini 

 makes a similar arrangement of burrows in the 

 ash-tree, and these are frequently evident in split 

 ash-poles that have been used for fencing, and from 

 which the bark has fallen. Tomicus typographic^ 



