THE ACULEATE HYMENOPTERA OF MID-SOLWAY. XXI. 



really abortive females). To compensate for their lesser bulk, most of the 

 species have males of more diversified and fully brighter colours than 

 those which adorn the females. Thus the males of Bombus terrestris, 

 pratorum, soroensis, Derhamellus, and lapidarius, are much prettier 

 than their respective partners. All the species already mentioned are 

 plentiful and generally distributed, with the exception of B.distinguendus, 

 a species that is by no means a common one, although it is almost 

 always present wherever rhododendrons are in bloom. Then we have, 

 in addition to the foregoing Bombi, B. cognatus, a very beautiful species, 

 of which I have seen only a very few examples. B. latreillellus is another 

 species of great rarity hereabouts; while B. schrimshiranus, though scarce, 

 may be found by diligent search. There is thus a total of eleven 

 species that occur in this district out of the entire number of sixteen 

 that are known as British species. Doubtless one or two more species 

 may yet be added to our local list by an assiduous collector. 



Nearly allied to the Humble Bees, and so similar in general aspect 

 to them that most folks never regard them as anything else, are those 

 curious parasites known to systematists by the generic name of Psithyrus 

 (Apathus). They have quite a strange history. They make no nests 

 for themselves, each of the five British species all of which are found 

 in this district being attached to certain species of Humble Bees. In 

 appearance they are exactly similar to Bombi, one main distinction 

 being that they are destitute of the corbicula, or pollen basket along the 

 outer portion of the hind tibiae, which when filled is so conspicuous in 

 the females and workers of the Humble Bees ; and not making any nests 

 for themselves and also leaving their young, like the cuckoos, to be 

 brought up by others, no workers are therefore required, so the sexes 

 consist of males and females only. They are much later in making 

 their appearance in spring than their hosts, for a wise provision of 

 Nature keeps them slumbering in their hybernacula until the nests of 

 the Humble Bees are fairly set going for the season. Then the females 

 of Psithyrus come forth and search for the nests of the particular 

 species of Bombus to which they are assigned. Having found what is 

 required they have no difficulty in entering, for they are so similar to 

 the rightful inmates of the unsuspecting household that they enter it as 

 freely as if it was all their own. Once in, eggs are laid in the cells pre- 

 pared for those of the Bombi, and the latter, never guessing at the 

 presence of foster children, bring up the young larvae with all the care 

 lavished on their own brood. Towards the latter end of the summer, 

 the old females of Psithyrus give place to a new brood that consists of 

 both females and males. They occur in great abundance on all the 

 wild flowers during the autumn months, the females that have been 

 paired at once proceeding into winter quarters, while the males die off 

 gradually till they finally disappear with the setting in of cold weather. 

 As to their relative abundance and distribution : Psithyrus rupestris, 

 which is said to be solely attached to Bombus lapidarius, seems to be 



