NOTES ON HYMENOPTERA. 109 



wRsps, or fossorial insects, are able to pui-siie the business of 

 their economy ; when a long succession of ungenial days 

 occur, numbers of the Hi/menojjtera must inevitably perish. 

 I have never observed any apparent diminution in the num- 

 bers 0^ Sijmenoptei'a after a severe frosty winter. Winters 

 during which periods of unseasonable mildness occur, suffi- 

 ciently so to rouse insect life from its torpidity, followed 

 by severe frosts, act undoubtedly most prejudicially on 

 Sf/menojitera. Some years ago I found a number of 

 Di])tera frozen stiff and covered with hoar-frost, so brittle 

 as to break with the slightest touch ; yet, on being very gra- 

 dually thawed, they became perfectly active and vigorous. 



I have also exposed the larvae of Anthophora acervorum 

 to a night of sharp frost in the month of January, yet these 

 were not in the slightest degree affected by it, or retarded in 

 their development. 



A combination of the causes enumerated, which com- 

 menced with the season of 1860, have, for longer or shorter 

 periods, continued up to the present time. The consequence 

 now is, that one family of Hymenopteraj the AndrenidcB, 

 or spring bees, have almost entirely disappeared from the vi- 

 cinity of London. These bees, formerly seen each succeeding 

 spring in multitudes on all the early spring flowers, are no 

 longer observed; the fields and banks are covered as for- 

 merly with flowers, but there are no bees to collect their 

 sweets. Previous to the year 1860, I have frequently cap- 

 tured, on a single fine day in the month of May or June, 

 thrice as many Hymenoptera as I have observed during the 

 entire season of 1863 ! 



Notwithstanding the temporary disappearance of our fa- 

 vourites, I feel confident of their re-appearance ; I cannot 

 possibly persuade myself that any of the species now pre- 

 served in our cabinets have altogether passed away, although 



