Joburgers all aflutter

Pioneer caper whites migration considered largest since 1966, with number extending into the billions

SHEREE BEGA

LIKE snowflakes, they’ve fluttered into the hearts of Joburg residents in the past few days, but the annual “migration” of pioneer caper whites is still clouded in some mystery.

Reinier Terblanche, a member of the Lepidopterists’ Society of Africa (Lepsoc Africa), who is researching pioneer caper whites (Belenois aurota), has discovered the butterflies are genetically pre-programmed to disperse: individuals coded for dispersal have different coloured pupae.

Lepsoc Africa says while the amount of pioneer caper whites filling the skies varies each year, it estimates the number currently on the wing extends into the billions.

The current “migration” of the butterflies – at least in the Joburg area – seems to be the largest since 1966, says Jeremy Dobson, chairperson of Lepsoc Africa.

The butterfly, also known as the brown-veined white in South Africa, occurs in southern Asia as far east as the Himalayas, in southern Arabia and most of sub-saharan Africa.

“The phenomenon we are seeing at present is not a true migration – the butterflies will not return – but is a dispersal event,” says Dobson.

The butterflies are largely flying from drier south-western areas to the wetter north-east areas. “All the butterflies that you see will be flying, generally, in a north-easterly direction.”

The core local population is found in the Kalahari, where the larvae feed on shepherds’ trees. “The dispersal is due to a population explosion and will probably last for a few weeks.”

While climate is “definitely a factor” , Dobson says there is not adequate data to suggest that climate change is behind the current wave.

“The triggers are twofold –- successive years of drought leading to drastic reductions of the parasites that prey on Belenois aurota, primarily the eggs, larvae and caterpillars. These parasites may be viruses, parasitic wasps, spiders, birds… Usually 99% of butterfly early-stages are eaten.”

Good rainfall, as has been experienced recently, leads to favourable conditions and a “population explosion” and subsequent “migration”.

“We don’t know how far individual butterflies fly in South Africa, but it seems likely that those that are high-flying and caught in favourable winds, can travel in excess of 1 000km.

“Those bobbing along near the ground and feeding in Joburg gardens along the way, probably have a range of a few hundred kilometres.”

The butterflies sleep at night on a plant or grass stem. “Not all the butterflies we are seeing come from the Kalahari; local pioneer caper whites will be emerging and joining in the ‘migration’,” he says.

Other species also disperse. “One of these is the African migrant (Catopsilia florella), which we believe migrate for similar reasons – occasionally, its numbers exceed those of Belenois aurota.

“A few species of moth ‘migrate’ in large numbers, generally at night and at high altitude, so it is not often reported. It’s even less well understood than the Belenois aurota migration.”

There are few significant threats to adult pioneer caper whites, “as we believe they are poisonous to birds and are subsequently left alone.

“A few will be caught in spiderwebs (or killed by spiders while sleeping) and several will be killed by cars.”

Belenois aurota only feed on plants of the caper family. “They are not an agricultural pest and will do no damage to suburban gardens.”

Dobson, 60, who has been fascinated with butterflies since he was a teenager and obsessed since he was 40, wants more South Africans to become enamoured with them, too.

“I think most people are unobservant about butterflies. At least the ‘migration’ seems to happening on such a scale it can’t be missed and has captured the public’s imagination.”

*Read about a new plan to arrest the global decline of insects on Page 10