It was difficult to miss the Blue Tiger migration through SEQ earlier this year. It made the news and went where few insect stories go, into social media and general public chit-chat. But where are they now and what were they doing here?
Blue Tigers are mostly a tropical butterfly and can be seen nearly all year round in North Queensland. They are migratory and fly south during spring and summer reaching southern Queensland, NSW and even Victoria. Huge numbers, probably in the hundreds of thousands, were seen widely across SEQ from November 2014 through to March 2015, with the highest abundance in January. If you stepped outside, they were impossible to miss.
This recent irruption of Blue Tigers was probably due to the high rainfall and hot temperatures in late 2014. These factors led to flush of new foliage on their main larvae host plant, Corky Milk Vine (Secamone elliptica) and the ability for lots of caterpillars to successfully pupate.
Corky Milk Vine contains several chemicals that are poisonous to many animals, but not to the Blue Tiger larvae. When the larvae eat Corky Milk Vine, the poisonous chemicals get passed on to the pupae and adult butterflies. These toxins then work to protect adult Blue Tigers from being eaten by birds, as birds have learnt that they get sick from ingesting Blue Tigers.
When cooler weather arrives, Blue Tigers will head back north passing through southern Queensland in April and May. They are known to congregate in huge numbers over winter, clustering on stems and vines in sheltered gullies in central and north Queensland. Individual Blue Tiger adults may live up to 6 months during which time they have migrated, bred and possibly over-wintered. Remarkable.
Despite there being a general migratory path of south in summer and north and autumn, Blue Tigers are often seen flying non-directionally or out to sea. There is still much to learn about butterfly migrations and invertebrate ecology in general, but the Blue Tiger migration is a welcomed spectacle of nature.
Article and photo by Deborah Metters