As far as insect invasions go, this one was flutteringly lovely. A rabble of white butterflies (yes, that is the collective noun!) descended on Johannesburg, South Africa’s largest city, on Saturday, causing exclamations of delight and a little confusion about where the winged invaders had come from. 

Before long, Twitter was all a-flutter thanks to butterfly spotters all across the city. 




As the swarm passed overhead, residents posted their backyard snapshots of the butterflies to Twitter and other platforms:

Joburg Butterfly 1
Image via Twitter user @joburgsister
Butterflies Joburg 4
Image via Bianca Ivanna Waskow.
Joburg Butterfly 2
Image via Niki Seberini.

So which species was responsible for the weekend's winged spectacle? According to lepidopterist and director of Conservation of Butterflies in South Africa Earle Whiteley, the migrants were brown-veined whites (known scientifically as Belenois aurota) – and their mass migration happens to be an annual event. 

The butterflies hatch on South Africa's western coast and then embark on an epic journey to Madagascar, laying their eggs along the route, according to Whiteley. "As they are going further north, some die and more join. Eventually, there are massive clouds of butterflies, reaching up to a kilometre into the air," notes Whiteley on Times Live.

For the tiny butterflies, the annual migration is no small feat, involving dawn-till-dusk flying (with regular pit stops for nectar to ward off dehydration) and some over-the-ocean travel to reach Madagascar. 

If butterfly tracking is your thing and you happen to live in southern Africa, you can help keep tabs on the migration (and do your bit for citizen science) by posting your butterfly sightings to this Facebook group. And don't forget to share them with us, too! 

Top header image: Dave Curtis, Flickr