Migration of <i>Catopsilia florella</i> in Botswana (Lepidoptera: Pieridae).
Keywords: Acraea, Africa, Belenois, Byblia, Colotis, Danaus, Ethiopia, Ethiopian, Eurema, Hypolimnas, India, Junonia, Kenya, Labiatae, Lamiaceae, Leguminosae, migration, Nymphalidae, South Africa, Vanessa, Zimbabwe
AbstractDuring March and April of 1991 a large migration of Catopsilia florella (Fabricius), comprising more than 1.5 billion individuals, crossed the whole of Botswana (about 1000km) with a direction just north of east-northeast. Numerically, this is one of the largest butterfly migrations ever documented. No major outbreak areas were identified and the evidence is consistent with breeding over a large part of the inner Kalahari and probably Namibia. The behaviour of the migrants was typical, though C. florella seems more ready to make small pauses at flowers or damp patches than is usual in migrants. The migrants unerringly resumed the migration even after several days of inactivity due to bad weather. The migrants were morphologically different from the parents and from non-migrant populations in the area. Migrant males were not sexually active while migrant females mated non-migrant males in some numbers, though these were always significantly outnumbered by migrants. The flight direction was maintained with great precision irrespective of wind conditions. Virtually all migrants left Botswana. The direction was the same throughout Botswana over nearly two months, precluding the possibility of spoke-like movement out of an out-break centre. A few cases of movement towards the northwest, presumably with an origin in the Orange Free State, were also noted. At times, half a dozen other species participated in the migration, but always at very low densities. Bushmen in the Kalahari use butterfly migrations as indicators of the imminent arrival of the vast herds of migratory ungulates from the same direction.