Wednesday, 1 February 2012

Butterfly migration out now!

African Caper White Belenois aurota
Beleonis creona African Common White
If you're anywhere near me at the moment and it's not dark, get off your seat and look outside. There is a phenomenal butterfly migration happening in the Arusha area at the moment - from my garden in Ilboru I'm counting around 100-150 white butterflies headed west over a 20m wide patch of sky every minute. Truly spectacular! I'd love to know how widespread the migration goes, so if your on safari and getting this on your mobile, let me know what's happening where you are too. I first noticed the movement yesterday and expect it will keep going for a while yet. The butterflies involved all seem to be the African Caper White B. aurota, though there could easily be some African Common White, Belenois creona (subspecies severina) in there as well. Look carefully for a while and there are one or two of the African Migrant Catopsilia florella a much larger and yellow tinged butterfly. The main difference between the two Belenois is that the male in the Caper White has a bar on the forwing and the Common White just as a spot - but it's not always easy to decide if it's a spot or a proper bar as there's lots of individual variation, so I might have got a few pics confused here. Let me know if you're better at these butterflies than me!

Belenoisa aurota African Caper White on the move now!
Migrations such as this happen every year to a certain degree, but in varying numbers - last year there were no major movements, two years ago we had something similar to this. These Belenois species all feed as caterpillars on members of the Capparaceae, for which they're often given the name Caper butterflies. The most common food plants in that family here are Maerua and Boscia species, and there's lots of those in the Maasai Steppe. Migrations like this have been recorded at erratic intervals for a very long time -I found a couple of old papers describing migrations of these species from the 1930s at a variety of times of year and with animals heading in a variety of directions, but nothing that really tells us what's going on in any detail. It's hard, really, to call such erratic migrations - they're probably moreproperly called 'erruptions' - when the population reaches a particularly high level and there's not enouch food the population en masse heads off to find new foraging grounds.

Painted Lady Vanessa cardui, Nr. Tarangire, Nov 2011
Other species do proper distance migrations too, of course, and I'll have to tell you about the Painted Lady Vanessa cardui some time, populations of which migrate from Europe to Africa and back again (other populations do a North American migration). But that will have to wait for another occasion, today is the day of the caper whites and erruptions! When they arrive in huge numbers their larvae have a massive impact on the food plants - they can completely defoliate (remove all the leaves) from thickets of Maerua, and substantially change the vegetation dynamics of the areas they settle. Such events no doubt give other species the chance to establish in the gaps that form and promote diversity in the system as a whole, but clearly show how the notion of 'balance' in nature is a myth - ecological systems are a complicated and dynamic system constantly changing, sometimes rapidly and dramatically.

Belenois creona - note the spot on the forewing, not a bar.
PS Just heard there are huge numbers going past Kili too, also headed West. Eouldn't it be fun if everyone in the region who reads this would be able to count a 20m stretch for 1 minute and record the predominant direction, then stick a comment in below so we can plot the direction and numbers across the region! I know there are lots of you reading this around Tanzania, even a few in Kenya...

UPDATE: Check the next post for an interactive map to add your sightings to!


  1. This eruption is absolutely incredible..I haven't manage to do some countings but I should be able to do this soon...((Arnold ))

  2. Thanks Arnold! Having started working my network so far I've discovered they're moving NW along the Pare mountains in middle sized numbers, heading west over Moshi and Arusha, carrying on west over Manyara but by the time the reach Eyasi they're heading South and I lose the trail there somewhere! No large numbers reported from central or western Serengeti yet, so that fits. I'm trying to find contacts further south and east to se what the story is elsewhere. I'll have an interactive map online somewhere soon, I hope - just been asking for help from some tech guys... Social media should let us learn something about this!

  3. Hi.i'm in kenya and two days ago i saw very many white butterflies coming these the west direction

  4. Thanks! Can you tell me where you are in Kenya and I'll add the observation to the map? Or feel ree to do so yourself. There are still some moving here and thfirst reported from northern Serengeti yesterday!

  5. We are in the Limpopo province in South Africa. It's 28 Dec '12 and the migration seems to have reached us with the butterflies moving North and (dispute in our family:-), some East. Does anyone know wheter they may be going back up in Africa? Where is their original habitat? We've been having unusual amounts of rain in SA, so the vegetation is good. This is highly exciting!! Sumali Smith

    1. Hi Sumali. Just read yr comments on migration of butterflies in Limpopo. We moved to Bela Bela (Warmbaths) this yr& have watched this migration in awe over the last 4 days & right now. There are millions of them& we were wondering where they are heading? Seems kike they r flying from west to east, right through the bush where we live & possibly going towards Modimolle/Nylstroom & maybe Polokwane? Can u or anyone else fascinated by this migration, give some comments? Thnx Yvonne

  6. I am in the west of Johannesburg and see the movement too!

  7. Hey all. We are in the Groot Marico area in North West Province and there are lots of butterflies here too. They seem to be going in a northern direction. I think the migration is more due to over population than a shortage in food resources as we had very eradic rainfall in the last month or two. Perhaps the rainfall and temperatures are also linked to their hatching numbers? Any thoughts? Mariante.

  8. hi
    we in Pretoria have been watching these butterflies for 3 days now
    they suck the nectar off the Lavender flowers in my garden

  9. We are 30 km north of Modimolle / Nylstroom. Migration been going for the last 7 days in a NE direction. Literally thousands upon thousands flying through the gorges. A site to behold. Have heard they are headed into Mozambique.

  10. Hi im in Sabie and its amazing!! A friend close to Hazyview has them too, he has heard they come from the N Cape and is going to Somalia!? They are so little, can that be true!! Keep us posted! Very curious. Winnette