20 [January, 



is now carrying on dipterological researches at Cambridge, has called my 

 attention to records of its autumnal iiivasions of houses in New York State and 

 Maine, invasions made in enormous numbers and in such a manner as to earn 

 for it the name of " cluster-fly." [See W. H. Dall, Proc. U.S. Nat. Mus., Vol. 5, 

 p. 63.5, 1882 : B. P. Mann, Psyche, Vol. 3, p. 378, 1882 : C. V. Eiley, Amer. Nat., 

 Vol. 17, p. 82, Jan., 1883]. Dall describes how these flies congregate in clusters 

 and accumulate behind pictures, under table cloths, etc. They prefer clean 

 rooms which are seldom used. It is also stated that " they like new houses " : 

 [compare the record, below, of a swarm of winged Psocidae in an absolutely new 

 house in England]. Riley remarks that the Pollenia do not enter houses in a 

 single swarm, as Chloropids have been observed to do, but gradually accumulate. 

 Such swarming of Pollenia rudis is not confined to America, for Keilin has been 

 informed that at the Chateau de Commanderie, near Orleans, certain rooms 

 seldom used have been invaded in autumn for a number of years in succession 

 by immense hordes of this fly. He regards the habit as being simply for the 

 purpose of hibernation. In this French chateau very many of the insects die 

 during the winter. To Keilin is due the interesting discovery that Pollenia 

 rudis passes its larval existence as an internal parasite in the body-cavity of the 

 earthworm Allolohophora. He has published a preliminary note on this (C.-E. 

 Soc. Biol. (Paris), Vol. 67, p. 201, July, 1909), and lias a full account of the life- 

 history now in the press. 



The present is an opportunity for putting on record a s\yarm of a totally 

 different kind of insects, namely, winged Psocidae, which occurred in 1913, in 

 the small house which I occupy on the outskirts of Cambridge. This building 

 was then quite new, having been commenced in the spring of 1913, and first 

 inhabited at the end of September. It stood on a plot of open grass-land, but 

 with ti-ees and shrubs at a distance of about 20 yards in two directions I fii'st 

 observed the Psocid swarm on September 13th, when it was thickest on the 

 ceiling of a small porch, numbers of the creatures being also present in the 

 rooms. I was told that they had already been in evidence for some time, causing 

 much annoyance to painters inside the house by sticking in quantities to fresh 

 white paint. The swarm lasted through most of October, its numbers gradually 

 dwindling towards the end of that month, though some of the insects continued 

 present even into November. On October 6th I recorded that the swarm had 

 existed almost continuously since September loth, the insects disappearing 

 ten^jjorarily from souk; rooms, only to re-appear in vast numbers elsewhere- 

 Unlike the flies they seemed to congregate more on ceilings than on windows, 

 forming dusky patches in particular parts of rooms. On October 19th I noted 

 that they were still numerous about the house, but much more scattered. 

 Specimens submitted to Mr. K. J. Morton were determined as belonging to two 

 species: Pterodela pedicularia Linn., and Ectopsocus hriggsi M'Lach. "The 

 former," wrote Mr. Morton to me, " is a well-known inhabitant of houses and 

 warehovises, sometimes appearing in great numbers ; but it is certainly curious 

 that it should have occurred in such quantity over a rather long period in a new 

 house." One may refer to Ent. Mo. Mag., 1900, p. 43, where M'Lachlan, under 

 the heading " Psocidae on the wing : a query," wrote thus concerning P. pedicu- 



