MASS MIGRATION: Sofia Draper with a blue tiger butterfly one of the many hundreds in the Gympie region.
MASS MIGRATION: Sofia Draper with a blue tiger butterfly one of the many hundreds in the Gympie region. Patrick Woods

Blue-winged migration has Gympie all a-flutter

ONE of the largest mass migrations for many years is under way in the Gympie region.

If you have not seen large numbers, easily in the millions, of blue tiger butterflies flying through the region over the past few weeks, you must have had your eyes closed.

In many places has been almost impossible to walk through a swarm of these 75mm wingspan butterflies.

At very irregular intervals, five-plus years, huge numbers of this species move eastward.

Occasionally, butterflies that have been banded are recorded in New Zealand as the swarms just keep heading east.

Some idea of the size of the swarm can be gauged by reports of huge numbers in mid-western New South Wales. Driving through a butterfly cloud meant car grills and windscreens were covered in yellow goo.

Blue tigers are a relatively long-lived species and are strong fliers, though weather fronts help with the trip across the Tasman.

Host plants are a number of native vines, but locally these vines have not been decimated by blue tiger caterpillars, so most breeding must have been further north or west and the swarms are just moving through this region.

The butterflies have been feeding on anything with a flower. Cotton bush, cobblers peg, blue top, praxalis and stinking roger have all had flowers covered in butterflies, but these are not caterpillar host plants, just a feeding stop for adults.

The 'blue' part of the name is a bit problematical as many adults have more white than blue markings on a dark background.

Male and females look the same but there is a small spot on the male's hind wing.

Mature larvae look a bit like an elongated bar code, with alternating black and white bands.

Green pupa with golden spots are attached at the top and bottom, often so close as to touch.