SOCIAL INSECTS 109 



associated with a large amount of independence. The case is that 

 of certain rather small " short-tongued " bees (species of Halictus), 

 which are represented in the British fauna. There are here no 

 workers, but by the united labours of a number of females a 

 branching underground passage is dug out at night, there being 

 a single opening to the exterior, and close to this an enlargement 

 or " hall " for the greater convenience of individuals wishing to 

 pass one another. Within this underground home each female 

 makes her own particular nest, consisting of ovoid waterproof 

 cells, and attends to her domestic duties after the fashion of 

 solitary species. A sentinel is said to be posted at the common 

 opening of the burrow, so that some understanding would seem to 

 be arrived at in the matter of mounting and relieving guard. But, 

 apart from this, the individuals living together have no more social 

 organization than the different families occupying a dwelling made 

 up of a set of " flats", who use a common stair and the same street 

 door. If the said families had constructed these by their joint 

 efforts the analogy would be more complete. 



The last example is a sort of side-branch in social evolution; 

 for a comparatively simple case in the direct series of adaptations 

 we may turn to the large insects familiarly known as Humble- Bees 

 (species of Bombus), which are well represented in our own 

 country, and live above or under the ground in communities 

 which endure for a single year only. They exemplify the 

 beginning of the caste -system, for in addition to males there 

 are three varieties of the opposite sex, i.e. queens, small females, 

 and workers, which in appearance and structure resemble one 

 another pretty closely. We do not find the same marked differ- 

 ences that exist between the queen and worker in honey-bees, 

 while the power of egg-laying is not restricted to the queen, 

 though she is the mother of most of the members of the com- 

 munity. The habits of several species have been closely observed, 

 and the succession of events is somewhat as follows. A queen 

 which has survived the winter begins her work as foundress of 

 a society when the spring is well advanced, and food in the form 

 of nectar and pollen is abundant. Selecting a sheltered spot, on 

 the surface or below the ground according to the species, she 

 successively constructs two or three large waxen cells, the material 

 for which is derived (as in social bees generally) from a number 

 of small glands that open on the under side of her abdomen: a 



