A swarm of white butterflies had many people asking questions about the insects’ origin and destination recently when they were seen flying around Johannesburg.

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According to Steve Woodhall, author of Field Guide to Butterflies of South Africa, the butterflies are called the pioneer caper whites and the Latin name for them is Belenois aurota.

Jeremy Dobson of the Lepidopterists’ Society of Africa (LepSoc Africa) also shared more details on the phenomenon.

“These butterflies are also known as the brown-veined white in South Africa, although LepSoc Africa is currently trying to standardise the English names of all butterflies found in Africa.”

While many say the phenomenon is a migration, Woodhall and LepSoc Africa confirm this is not true.

“It was not a true migration because the butterflies will not return, but was a dispersal event,” said Dobson.

“They were flying from the dry southwestern areas to the wetter northeast areas. All the butterflies were flying in a generally north-easterly direction,” said Woodhall.

According to LepSoc, a recent news article stated that the butterfly migration originated from the West Coast and that they were flying to Madagascar.

“In SA the start of the dispersal relay was in the Kalahari, and while it’s not impossible that one or two adults may reach Madagascar, this is definitely not their intended destination,” said Dobson.

According to LepSoc, the dispersal in the Johannesburg area was the largest since 1966.

“The dispersal is due to a population explosion.”

Woodhall said the core population of Belenois aurota comes from semi-deserts in SA, like the Kalahari and Karoo regions, where the larvae feed on shepherd’s trees called Boscia albitrunca.

“Belenois aurota occurs in southern Asia and as far east as India and the Himalayas, in southern Arabia and throughout most of sub-Saharan Africa.”

Woodhall said the swarm is related to the recent drought experienced in southern Africa.

“After a drought and good rains, this is when you likely see to the swarm dispersing.”

Climate is definitely a factor, although LepSoc stated there is adequate data to suggest that climate change is responsible for the current wave of pioneer caper whites.

Dobson outlined triggers as twofold.

“Successive years of drought leading to drastic reductions of the predators that feed on Belenois aurota, primarily the eggs, larvae and caterpillars. These predators may be viruses, parasitic wasps called parasitoids, robber flies, spiders and birds.

“Good rainfall, as we’ve experienced recently, leads to favourable conditions and a population explosion of Belenois aurota and subsequent dispersal. Those bobbing along near the ground and feeding in Johannesburg gardens along the way probably have a range of a few hundred kilometres. They will sleep at night on a plant or grass stem. Female Belenois aurota will be making stops and laying eggs on suitable larval food during their journey. The amount varies from year to year, but we estimate that the number of butterflies currently on the wing extends into the billions.”

Threats

There are few significant threats to adult brown-veined whites.

A few will be caught by robber flies, or trapped in spider webs or killed by spiders while they are sleeping, and several will be killed by cars and trucks, according to Woodhall.

“Belenois aurota caterpillars feed only on plants of the caper family. They are not an agricultural pest and will do no damage to suburban gardens. Their caterpillars are not army worms or lily borers, nor will they cause African horse sickness,” said Woodhall.

One of the LepSoc Africa members, Reinier Terblanche, is conducting research on Belenois aurota.

One of the amazing things he’s discovered is that butterflies are genetically pre-programmed to disperse. Individuals coded for dispersal have different-coloured pupae.

Woodhall will release a new book towards the end of February that butterfly enthusiasts can look forward to.

For more information on butterflies, like The Great Little White Butterfly Migration group on Facebook.

Woodhall’s three tips to not be a threat to dispersing butterflies

1. Don’t use insecticides on them.

2. Enjoy and appreciate them.

3. Don’t chase them away from your garden as they won’t damage any plants.

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Today in Modderfontein pic.twitter.com/qYUjvBnJcv — Saajid Hoosen (@IamSaaj_) January 28, 2020

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