Butterfly migration on the coast

Article and images by Michelle Gleeson, Entomologist, Director and Presenter, Bugs Ed

At certain times of the year, usually in the warmer months, the size of some insect populations can explode. A combination of favourable weather conditions and an abundance of food can send the rates of breeding and egg–laying skyrocketing and before you know it, tens of thousands of insects descend upon our homes and gardens.

Other insects, such as some types of butterflies, migrate in large masses – flying long distances in a purposeful manner, ignoring food and potential spouses as they move towards their destination. The end point may be a breeding site where there is an abundance of plants on which to lay their eggs, or it could be a place for over-wintering – a warm, sheltered location where adults cluster together to wait out the coldest months of winter.

These large ‘plagues’ are often witnessed by the public and sometimes attract the attention of the media. Some species are admired for the spectacular, others may cause damage to crops and gardens. While these fluttering masses of insects may invade our personal space for a short time (e.g. flower beetles clustered on washing, butterflies splattering on car windscreens or plague locusts blundering into our face and hair) it is a mild annoyance compared to the excitement of witnessing such a grand and extraordinary phenomenon.

Two of the butterflies which migrate through the Coast are the caper white butterfly and the blue tiger butterfly.

Caper white butterfly - Belenois java

Caper white butterflies are handsome white insects with yellow and black markings. They can form large migrations in spring and summer, which have been dubbed by some as ‘butterfly snow’. At its peak, as many as 650 individuals have been witnessed passing through a 50 metre line of sight within the space of an hour. The butterflies move at a steady speed, around 2–3 metres off the ground. Unfortunately, at this height, many individuals become splattered on the windscreens of our cars.

The exact nature of these migrations is quite baffling and the direction of flight often depends on your locality. Queensland populations tend to fly further north during the spring, whereas those in New South Wales and Victoria, fly south.

Caper whites breed in vast numbers on caper bush, a shrub that grows commonly, further inland from the coast of Australia. The larvae reach huge populations, often completely stripping the foliage from the plant. The migrations of the adults are almost certainly linked with the butterfly’s search for suitable plants for egg laying, as well as warm, mild temperatures for optimal survival.

Size: adult wingspan 55 mm.

Goodie or baddie? These migrations are a beautiful sight, however a trip through the car wash may be needed.

Blue tiger butterfly - Tirumala hamata

Blue tiger butterflies are large dark brown or black butterflies, with streaks of light blue markings dotted across their wings. They can be found breeding in coastal and monsoonal rainforests, where their caterpillars feed on certain species of vines. From time to time they form huge migrations during spring, usually making their way southward. In autumn, the butterflies fly north in search of over-wintering sites, where they wait out the cooler months huddled together on trees and vines in dry gullies and creek banks.

Size: adult wingspan 70 mm.

Goodie or baddie? A beautiful butterfly to watch flutter by.