By Dr Chris Burwell, Senior Curator of Insects at Queensland Museum
This year has seen a bumper summer and autumn for butterflies in Queensland with a great diversity of species and huge numbers of some species on the wing. They have provided a bright distraction from the anxious times in which we have been living during the current health pandemic.
As we head towards winter there has been a noticeable decline in butterfly numbers; but where have they gone? Unfortunately, most adult butterflies are short-lived, surviving from weeks to a few months, so many have been dying off throughout summer and autumn. The drop in numbers that we are now seeing is because there are far fewer freshly emerged butterflies to replace those that are dying off. Many of the butterflies that are still out and about are nearing the end of their lives and looking worse for wear with tears and rips in their wings. Some are so ragged that it seems amazing that they can still fly.
As the days become shorter and temperatures drop, butterfly breeding is grinding to a halt, especially in subtropical Queensland. In warmer tropical Queensland, some butterflies can breed throughout the year but others curb their reproduction during the dry season when plant growth is low. So how do butterflies survive through the colder, drier winter months in southern Queensland? Different butterfly species have different strategies. A few, such as Blue Tiger, Tirumala hamata, and Common Crow, Euploea corinna, butterflies pass the winter as adults, many individuals aggregating in sheltered locations along creeks and gullies.
Most butterfly species, however, sit out the winter or dry season as immatures, either as eggs, mature larvae or pupae. This strategy is referred to as diapause, where development is stopped until conditions become favourable. When temperatures rise the following spring and rainfall increases the eggs hatch, the mature caterpillars begin to feed, and adult butterflies emerge from the pupae.
As winter approaches, most adult butterflies have been on the wing for some times and are beginning to show signs of wear and tear. This Meadow Argus, Junonia villida, has a ripped hindwing and this Lemon Migrant, Catopsilia pomona is looking ragged.