A swarm of butterflies in Sarawak
This brief note by R. Shelford (1903) records an abnormal swarm of the butterfly Cirrochroa bajadeta in Sarawak, which he attributes to a comparative drought (rainfall well below the 75.17-inch average) and the exceptionally favourable monsoon conditions for insects.
Summary
Shelford links the butterfly swarm to a dry period and corroborates the broader insect-favourable conditions with three additional observations: an increased number of social wasp and bee swarms over the preceding three months; a swarm of dragonflies reported by Captain A. Balser aboard the s.s. Rajah of Sarawak on 20 January, approximately 50 miles west of St. Pierre Island, moving northward in unsteady winds; and a swarm of Pierine butterflies (probably Catopsilia crocale, Cram.) observed by Mr. H. B. Crocker at Paku, Upper Sarawak, on 27 January, flying in a solid phalanx roughly 20 fathoms long by 8 fathoms wide in a westerly direction (p. 204).