142 
NYMPHALIDAE 
In 1879 the first migratory swarm appeared in North Africa 
in the middle of April. At Barcelona and Valencia enormous 
numbers occurred at the end of April and reached the island 
of Minorca on the first three days of May. On June 15th 
vast swarms passed over Sevres, flying all day in a north- 
north-westerly direction. Similar flights were seen at Stras- 
burg passing in countless numbers to the north. At Angers, 
on June 10th, an immense swarm flew over the city ; it was 
estimated that between 40,000 and 50,000 passed along a 
single street in one hour; they were flying so low that 
pedestrians were inconvenienced by them. At Bisheim, on 
June 8th, the same phenomenon was observed and their 
numbers were so enormous that they darkened the day. On 
June nth the flight that passed over Steyer, in Austria, was 
*so great that between one and two o'clock p.m. 90 to 100 
per minute were counted in the breadth of 100 paces, the 
swarm being estimated above 1,000,000. Similar vast swarms 
were encountered in other places. Again, in 1903, a sudden 
and great invasion of these butterflies occurred in the autumn. 
They arrived in hundreds of thousands along the southern 
and eastern coasts and dispersed over the whole of the British 
Islands. The flight was so vast that it extended from the 
Shetlands to the extreme south of England and Ireland. 
Their numbers were so prodigious that they swaimed along 
the whole of the eastern seaboard, from Durham to Kent, 
and wherever observations were made on the Scottish coast, 
they were abundant. The first arrivals of this vast invasion 
reached our shores on September 18th, and the flight con¬ 
tinued for five or six days, their numbers increasing daily. 
The migratory habits of this butterfly were known as long 
ago as 1828, as we find in the “ Annales des Sciences Naturelles " 
an immense swarm of V. cardui recorded as seen in May of 
that year in one of the cantons of Switzerland. The flight 
occupied several hours in passing over the district where they 
were observed. 
This butterfly has often been seen on the wing long after 
sunset, and has been attracted by artificial light. This 
nocturnal habit tends to prove that these butterflies migrate 
at night as well as by day ; obviously, the long distances they 
travel undoubtedly necessitates a considerably longer time 
