182 THK extomolohist's record. 



22n(l, iHHd, they swarmed in millions at Heli.i^oland, and continued to 

 do so until the 26th, when the wind l)ecamc northerly, and next morning 

 not a sint^le one was to he seen, (iiitke's own account of these visita- 

 tions su,Q:,i,'est the some'what regular appearance of these insects on the 

 island. He notes {Hduiolawl as cm oniiflioloi/ical ohsi'rratorti, p. 87) that 

 the regiilar but temporary appearance, in millions, of lAhclUda (jiiad- 

 rimacKlata always takes place in Heligoland just before a thunder- 

 storm. Countless swarms of these insects, he says, make their appear- 

 ance all of a sudden during the cahn, sultry hours just preceding 

 such a disturbance, but the direction whence the insects proceed cannot 

 be ascertained. They do not arrive in swarms or companies, but 

 solitary individuals or scattered groups congregate on the spot in one 

 vast throng. The assembhng individuals or groups must, however, 

 follow each other in very rapid succession, for, in a short time, the 

 face of the clitf, all the buildings, hedges, and dry twigs on the island 

 are covered with them. The insects disappear as suddenly as they 

 appear, so that hardly one of them is discoverable on the following 

 morning. It is not known whether they proceed further west. It is 

 certain, however, that they do not remain here, nor does one find them 

 lying about dead after a thunderstorm. 



With regard to the Weimar migration already alluded to, we note 

 that in the Ma;/, nf Xat. Hist., 1889, p. 516, Weissenborn records that 

 on May 30th and 31st, 1839, immense cloud-like swarms of I'latr- 

 triiiii (Icinrssiiiii passed in rapid succession over the town of Weimar and 

 its neighbourhood, the general direction of the swarm being from south 

 l)y west to north by east. The migration was also observed in all the 

 villages situated a few miles to the east or west. The insects arrived 

 in a vigorous state, some of the flocks flying as high as 150ft. above 

 the level of the Ilm and striking against the windows of a house 

 situated on an eminence, others passing through the streets. The 

 observer attempted to collect details as to the migration, and ascer- 

 tained that cloud-like swarms were seen at Gottingen, on June 1st; 

 Eisenach, on j\Iay 30th-31st, flying from east to west; at Calais, June 

 14th, flying in the direction of the Netherlands, but the latter were, 

 from the description, possibly another species. Local swarms of 

 dragonflies were also observed in the neighbourhood of Leipzig, Alsle- 

 ben, Aschersleben, and Halle, the examples captured at the latter place 

 showing that the species was LibcUiila qKadriiitacidata, the swarms 

 arriving on the afternoon of INIay 30th, a short time before a thunder- 

 storm, and flying very rapidly from north to south. On JMay 31st 

 similar flocks followed in the same direction, most of them passed at a 

 height of 7ft. to 8ft., catching insects as they flew on. The SAvarms 

 were everywhere observed within a league of Halle in almost every 

 direction, while the whole valley was inundated by the river Soale. 

 //. iiidiilriiiiaciddtd is noticed as being usually scarce at Halle, and /'. 

 dr/nrssuiii also scarce about Weimar. The migrations appear to have ex- 

 tended from 51' to 52' N. lat., and within 27 ' 10" to 30' 1^. long, of Ferro, 

 but the migration observed at Calais suggests that they were possibly 

 spread over a great part of I'.urope, wherever suitable meteorological 

 conditions prevailed. The last migration of Odonata preceding this, 

 observed at Weimar, had taken place June 2sth, 1816, the species then 

 also being /'. ilfinrssmn. The year 1816 was extremely wet, and 1817 

 equally so, yet no migrations were observed in the latter year. The 



