1889.] 207 



totally absent in this neighbourhood, and also the common species of 

 Sphecodes, pilifrons, Thorns., and similis, Wesm. However, as soon as 

 I visited other localities where these Halicti occurred, I at once took 

 the above mentioned species of Sphecodes; consequently, knowing 

 how other species of the latter genus were always to be found with 

 other species of the former, I came to the conclusion that there must 

 be some connection between them. 



Last July I was pleased to find burrowing in the clay, just on the 

 edge of a ploughed field, numbers of Halictus ccanthopus, Kirb. ; at 

 this time they were much worn, being all hibernated females. On the 

 flower heads of Centaurea, Senecio, &c, they positively swarmed, and 

 around their burrows and in their company I took a short series of 

 Sphecodes spinulosus, von Hag., the finest species of the genus. No 

 doubt I could have taken many more, but it was not nearly so plentiful 

 as the Halictus. It is a singular fact that, though I have hunted in 

 the same spot in previous seasons, I have never before seen a single 

 specimen of either of these two species. Their occurrence in this 

 way, together, is certainly strongly in favour of the parasitic view. 



The prevalent opinion that they are ' non-parasitic seems chiefly 

 to be founded on the following observations : — first and foremost, 

 Sphecodes have been seen to form their own burrow ; secondly, they have 

 been noticed in spots where Halictus has not ; and lastly, Prosopis 

 has proved to be no parasite, though many Hymenopterists once re- 

 garded it as such, as well as Sphecodes. 



As to the first observation, I, only the other day, saw Sphecodes 

 gibbus, Linn., $ , forming a burrow in a bare spot in the clay ; but 

 this argument can best be met by considering the habits of other 

 parasitic insects. Some, such as Melecta, appear to be obnoxious to 

 their host ; others, like Nomada (at least certain species of this 

 genus), are allowed to enter the burrows of Andrena, &c, without 

 hindrance. In May and June, when Anthophora is most busy, I take 

 females of Melecta commonly, hanging to the asparagus, twigs of 

 barberry, &c, in our garden in the evening and on wet days. They 

 hang down by the mandibles alone, and are very conspicuous in some 

 cases. Nomada ochrostoma, Kirb., I take in the same way, but usually 

 on the dry flower-heads of grasses. It assimilates very well with its 

 place of rest, reminding one strongly of Thanaos Tages on rush 

 blossom, or Anthocharis cardamines on white Composite, amongst the 

 Lepidoptera. Possibly, therefore, this Nomada is obnoxious to its 

 host, Smith's Andrena xanthura. 



In weather such as we have had this year these species are rapidly 



