Last summer we had an explosion of Cabbage White Butterflies which are an introduced species, and quite a few native Imperial Jezebels – and this year we are blessed with another black and white butterfly boom – this time the Caper White Butterfly!
Caper White Butterflies (Belenois java) can be distinguished from Cabbage Whites(Pieris rapae) by the strong black venation pattern and margins on their wings, with yellow -orange spots on the underside of their wings. Cabbage whites have no yellow-orange colouring.

A Caper White Butterfly, Ed Williams

Cabbage Whites, Imperial (and Painted) Jezebels and other local butterflies are seen in good numbers when their caterpillars do very well and many survive to adulthood. In the case of the Caper Whites the large numbers we are seeing locally is due to the fact that they are on migration!
Caper Whites are so called because their larvae feed on the leaves of trees and shrubs in the Caper Family – Capparis, and also the Australian Sandalwood (Santalum spicatum). But these species don’t grow locally… Capers such as Wild Orange (Capparis mitchelli) and Bush Caper (Capparis spinosa) occur in the drier, inland parts of Australia.

The species is strongly migratory – flying fast at about head height – sometimes for distances of over 3000 km. But even butterfly experts are mystified as to why adult Caper White butterflies would embark on these southerly migrations that take them away from their food plants.

Some sources suggest that their movements are related to weather – and hot northerlies blow them out of their usual range towards the east coast. Our recent full on cold snap was, paradoxically, related to the intense heatwave conditions occurring inland. And then a couple of weeks later – thousands and thousands of these butterflies appear, so the notion that warm northerlies blew them in kind of fits. Migration is also very much part of their genetic make-up – this genus has closely related butterflies in Africa that also undertake mass migrations.

So as the adults are passing through our region they are happily drinking nectar from all sorts of plants – I have seen them sipping on Rosemary, Daffodil and Onion Weed in my garden, and in the native forest here and near Castlemaine dozens of daisies and flowering native shrubs.
During a Caper White Butterfly migration event some adults find their way to the caper plants at the Royal Botanic Gardens Melbourne and successfully breed there!

Caper White Butterflies mating by Karin de Mamiel

Sometimes the male and female butterflies migrate separately for example in October 2000 50-100 males were observed sheltering form the wind at Point Addis Victoria.
The first day I observed the butterflies I saw them both here and in Castlemaine, and at first they were all males. But then here at home I noticed some butterflies with much thicker black margins -the females! Pictured right.

The day before yesterday on a lovely warm day I saw a female perched low on our lawn, and a male approaching her, bumping bodies then backing away and hovering above her about 10 -15 cm away, then repeating the dance. I don’t think they actually mated – and after a few tries she flew off.
I am considering planting an Australian Native Caper ( Capparis spinosa )  here – but I hear Chris my husband already tried! They like full sun and well drained sandy soil, both in short supply here on out bush block! Perhaps a large pot…. It would be lovely to help these butterflies with this strange mystery migration….