33 



retreat. This is scarcely surprising, as the most pressing require- 

 ments for their purpose are absence of damp and shelter from the 

 wind. That dwelling houses are warm in addition to being dry and 

 sheltered, is probably a misfortune from the insect's point of view, 

 as the artificial warmth tends to interfere with the winter slumber. 

 Probably outhouses, hollow trees, timber stacks, etc., are much more 

 Batisfactory as hibernacula. The Vanessid butterflies, and many of 

 the hibernating moths, are frequently found in these situations. 

 Caves also are sometimes much frequented by certain species, on 

 one occasion, for example, I found considerable numbers of Sroli- 

 opteryx libatn'.v and Triphosa diibitata on the walls and roofs of caves, 

 which habitat they shared with numerous gnats and Long-eared 

 Bats, but the Vanessid butterflies Avere altogether wanting from the 

 association. Gonepteri/x rliaiiDii frequently shows a marked prefer- 

 ence for the interior of a thick holly bush as a winter resort, though 

 it will sometimes pass the winter on an exposed stem. 



A peculiarfeatureabout these hibernating insects is the tendency 

 many of them show to congregating in large numbers. Amongst 

 the Diptera several species exhibit this habit, frequently forming 

 mixed swarms. Thus Ashworth notes a case of the Anthomyiid 

 Liiiniop/iora septemnotata forming the bulk of the swarm, though the 

 JMiisci'la, Pijriilia eriophthahiia, ]\]uscina stabnlans, L'lotocallipJiora 

 ijrcexlanilica, and Pollenia rinUs were present in smaller numbers. 

 Further, the Chalcid parasite, Pteroinaliis (SteiKnnobis) mnscanim is 

 usually found mingled with these swarms of Diptera. Another 

 Chalcid, l'teru))ictliis deplanatus (20), is also found sometimes in in- 

 credible numbers, and is almost uncanny in its ability to creep into 

 minute crevices, getting into picture frames, frequently between the 

 pictures and the glass, into drawers, books, etc. It is of interest to 

 note that of both species of Chalcididce mentioned the swarms consist 

 entirely of females, at any rate of many thousands examined I have 

 never found a male amongst them. Of some of the flies, too, only 

 females are found in the swarms. Those of Liwnophora septeni- 

 notata and Mnacina stabidans, on dissection, have been found to 

 have their receptacula seminis full of spermatozoa, though the 

 ovarian tubes are immature. Evidently then these flies are impreg- 

 nated before hibernation, and on resuming activity in the spring will 

 feed up and develop their ovaries and soon be ready to lay fertile 

 eggs. Of other species such as Pyrellia erioplithalma , Pollenia VKdin, 

 and AphiucJiccta nifipes, both sexes have been found in the swarms. 



The Vanessid butterflies sometimes show a tendency to congre- 



