16. BOMBTJS. 197 



the nests of the latter are greatly increased or diminished by the 

 state of the weather : in fine dry seasons nests have double the 

 number of inhabitants to what are found in them in wet unfa- 

 vourable ones. A nest of B. sylvarum, found towards the end of 

 August, had only three females, about half a dozen males, and a 

 dozen workers, while several pupae were dead in their cocoons. 

 This was after a wet summer and autumn ; the insects themselves, 

 particularly the workers, were mere dwarf examples of the species. 

 The average number of the population of B. muscorum, according 

 to my observation, has been, in autumn when all the sexes are 

 found, about 120 ; 25 of these were females, 36 males, the rest 

 being workers. 



The division which is here named surface-builders contains those 

 species usually called moss-builders or carder-bees, which are said 

 to card or comb and cleanse the moss which they use in the construc- 

 tion of their nests. Thus we find it recorded that " to these nests 

 a moderately long arched passage is formed of the same material 

 (moss) of sufficient size to permit the free passage of the bees to 

 and fro." The nest is described as having a " vaulted covering, the 

 inside of which is further strengthened by being plastered with a 

 coating of wax." Whatever may be the habits of these bees in 

 other parts of the world, my own observations have failed to detect 

 in any of the numerous nests of B. muscorum, B. venustus, B. elegans, 

 or of B. sylvarum any plastering of wax inside the covering, neither 

 have I observed any long arched passage leading to the nest. With 

 regard to the materials used in the construction of nests, I have 

 found usually an admixture of moss, but very frequently not a sprig 

 of that material ; bits of grass, usually the tender blades dried — 

 in fact a small bundle of hay has formed the covering, the 

 blades on the inner surface being apparently more or less adhering, 

 probably from the insects having bound them together with a 

 gummy secretion or saliva. Several instances have come to my 

 knowledge of the sagacity of these insects in making use of 

 the nests of birds, and of their adapting them to their own re- 

 quirements. One was recorded in the former edition of this work. 

 Dr. William Bell observed the nest of a robin built in the porch 

 of his cottage at Putney ; some time afterwards he found that a 

 humble-bee had taken possession of it, and had adapted it to its 

 own purposes. Unfortunately the nest was destroyed before he 

 had ascertained the name of the species; but, judging from the de- 

 scription Dr. Bell gave of the bee, there can be little doubt of its 

 being B. joratorum. Mr. Y> T alcott, of Bristol, communicated a simi- 

 lar account of finding the nest of a robin invaded by B. derhamel- 

 lus, the eggs of the bird being covered with the accumulation of 

 pollen and honey stored up by the bees. Mr. Walcott added to this 

 account : — " I have in two previous instances found broods of the 

 same bee in birds' nests." Another correspondent gave me the 

 following account of B. muscorum : — " This insect took possession 

 of a wren's nest at Holmbush, near Brighton ; I had observed the 

 bird building, and afterwards was astonished on finding that a bee 



