Visitors to the Kruger National Park travelling through Gauteng, Mpumalanga and Limpopo recently, must have noticed that they were in the company of thousands of little white butterflies, fluttering steadily in more or less the same direction. These are the brown-veined whites (known in Afrikaans as the grasveldwitjie), the colouring of the undersides of their wings giving them their name, their scientific name being Belenois aurota.
The butterflies originated from the Southern African interior, where most of their larval hostplants grow naturally. The good rains in January and February and the subsequent rush of new leaves saw the females laying their eggs on their specific food plants in great abundance. Within days millions of tiny caterpillars hatched and ate their way steadily but surely "out of house and home".
These caterpillars then pupated and emerged as butterflies, to go in search of a mate and a new food plant to lay their eggs upon, and so the cycle continues until the larval food plant supply is finished. This phenomenon is known as population explosion.
Adults that have as yet not procreated will disperse to look for their food plants elsewhere and will somehow keep moving in a south-easterly direction towards the sea off Mozambique. Most will unfortunately perish en route due to total exhaustion. A few nectar plants in your garden helps to sustain the travellers.