52 Insect Architecture. 



tions is not a very easy task, because the tunnel does not 

 run straight, but turns aside when a stone or any similar 

 obstacle comes in the way, and in getting out the stone the 

 burrow is mostly broken. The only method of digging out 

 the nest successfully is either by pushing a small twig up 

 the hole, and using it as a guide, or by filling the entire hole 

 with cotton wool, so as to prevent the earth from falling in. 



The commonest species is Andrena albicans. Its length is 

 rather less than half an inch, and its colour is black, with a 

 thick coating of rich red hair on the upper part of the thorax. 

 This species is plentiful on the continent, and is found as far 

 south as Italy. But it is equally capable of enduring great 

 cold, as it has been captured in the Arctic regions. Some- 

 times the bee will not trouble itself to make a number of 

 separate burrows, but will drive short -supplementary tunnels 

 from the side of the first burrow, so that they all open into 

 one common entrance. 



The Andrense are remarkable for the parasites with which 

 they are infested, the most curious of which is that tiny 

 strepsipterous insect called the Stylops. 



One of the Andrense, called Colletes Daviesana, is remark- 

 able for the character of its burrow. Like many of the 

 insects which have already been described, it seems in- 

 different whether it burrows in sandbanks or into the mortar 

 of walls, provided that in the latter case the mortar is soft 

 and friable. 



The insect burrows a hole which is very deep in proportion 

 to its size, the little bee being only the third of an inch in 

 length, and the burrows some eight or ten inches in depth. 

 When the mother Colletes has finished her tunnel, she lines the 

 end of it with a thin kind of membrane, which has been well 

 compared by Mr. F. Smith to goldbeater's skin. This lining 

 is intended to enable the bee to store honey in the cell, as, if 

 there were no such protection, the honey would soak in the 

 ground and be lost. 



Having stored up enough food for a single offspring, she 

 shuts it off by a partition of the same membranous substance as 

 the lining. Her next care is to make a thimble-like cup at 



