Butterflies take a winter break
Common Crow Butterflies have a neat trick for dealing with dry winter weather. Around June or July, they gather in large numbers, settle down among the trees and put their lives on hold for months at a stretch. When these Crows hang out in the thousands it can be a spectacular seasonal sight in the bush.
The Common Crow butterfly (Euploea core corinna) can be found over a large part of Australia, from the Pilbara in north west through the Northern Territory and all down the east coast.
They prefer coastal areas in the tropics and subtropics, but are extremely versatile and can survive even in drier inland areas, particularly in cool sandstone and limestone gorges and around natural springs.
European settlement has been good for the Common Crow. It's frequently seen in gardens in cities and towns, where it has managed to adapt to a number of introduced food plants — oleanders, mandevilla (Chilean Jasmine), trachelospermum (Chinese Star Jasmine), Cryptostegia grandiflora (rubber vine), and stephanotis to name just a few.
Some people also know the Crow as the oleander butterfly, after the oleander that it's often found on.
In Canberra the oleander may be the sole reason for the butterfly's habitation. In the wild they feed on a wide range of Australian plants including native figs, native hoyas and parsonsia.
Aggregating against adversity
It's a useful strategy for some butterflies to form aggregations in times of adversity, often to avoid unfavourable seasonable conditions. In 1979 a group of students at Griffith University discovered a large number of butterflies clustered together in a gully on the university campus. Entomologists Roger Kitching and Myron Zalucki went to check to it out and talked to the ABC's Peter Wear about what they found.
They found between 1000 and 2000 butterflies gathered, or aggregated, together. There were twice as many males as females and all the Crow butterflies in the area had aggregated as there were no sightings of them in adjacent areas.
When: June - July
Where: From the Pilbara in north west Australia, through the Northern Territory and all down the east coast. They prefer coastal areas in the tropics and subtropics, but are extremely versatile and can survive even in drier inland areas, particularly in cool sandstone and limestone gorges and around natural springs.
Other info: As many as two thousand butterflies aggregate together in times of adversity.
It can be tough being a butterfly
Butterflies that reach adulthood just before winter are in for tough time. The host plants have no fresh foliage for the larvae to feed on and there are few nectar sources available for the adult butterflies. Adult Crow butterflies get through winter by going into a kind of dormancy or diapause. We don't know for sure yet what triggers this behaviour. In the Monarch Butterfly it's the cold, but it could be a number of things for the Common Crow. This behaviour is called overwintering. And they do it altogether in aggregations - there's safety in numbers.
The Common Crow belongs to a group of buttterflies known as the the danaines, nearly all of which contain poisonous compounds which make them unpalatable to predators like birds and predators. Once the predators taste one or two butterflies they quickly leave them alone.
Many danaine butterflies cluster for protection in this way. The Monarch butterfly in the USA, famous for its winter aggregations, is also a danaine.
Putting your life on hold is common in other butterflies but mostly it is done in the larval or pupal stages, especially amongst temperate and cool climate species. Doing it as an adult, like the Common Crow, is much less usual.
No sex please, we're overwintering
Overwintering buys adult butterflies time. In summer an adult Crow butterfly lives for about one to two months. But a Crow butterfly that has overwintered can live as long as 9 months. And those few extra months mean the winter butterflies can make it through to the spring, a much more favourable breeding time. About one quarter of the female Crows at a cluster site near Townsville, studied by Dr. Elly Scheermeyer were virgins with no ovarian development.
While they are overwintering, the butterflies are in a state of reproductive dormancy and their life is on hold. They don't eat or drink very much and the fat content of their bodies declines steadily from around 25 per cent to 18 per cent over about a month. Despite the fact that they're all together in the one spot, they don't breed during the aggregation.
Where to see the aggregating Common Crow
The Common Crow is a large butterfly — black with small white spots on the edges of the wing and larger spots further in.
The aggregating Crows like cool spots where the temperature doesn't fluctuate too much, for example, gorges, gullies, swamps and around lagoons. They particularly like dead casuarina trees, paperbarks and rubber vines. They spend their time resting on vegetation one to six metres above the ground. There can be thousands of them at any one location.
Good places to see these winter aggregations are sheltered coastal sites and offshore islands in the tropics and subtropics of northern and eastern Australia. The most spectacular aggregations are in the north around lagoons or environmental parks near Townsville, Cairns and even Rockhampton. People lucky enough to be spending winter in the Whitsundays or Horseshoe Bay on Magnetic Island off the Queensland coast are especially likely to see them.
Further south in Brisbane the winter aggregations are much smaller. Here they last from about mid-May to early July. In the north they begin later and end later.
If you're in the Northern Territory, inland Common Crow aggregations in winter months can be seen at Nitmiluk (Katherine Gorge) National Park. In shady, narrow Butterfly Gorge (which joins Katherine Gorge) tourists can walk through monsoon rainforest and see the butterflies settled on the trees and rockwalls.
There's another butterfly gorge near Douglas Hot Springs, 130 K north of Katherine. Crows also congregate at Mary River in the Northern Territory, Porcupine Gorge near Hughenden, and in rubber vine thickets along the Burdekin River near Charters Towers and other inland rivers.
What do they do while they're overwintering?
Because they don't eat or drink much, they need to stay in a moist environment. They also occasionally need to feed, so they like to be near flowering plants such as paperbarks and winter herbs.
The butterflies will occasionally go on desultory flights in search of nectar sources or a better cluster site. Most return within minutes to the main cluster site. None of these flights are mating flights.
By midwinter quite a few plants are beginning to flower and when new growth is appearing on host plants the butterflies may start to disperse. As soon as host plants have young shoots, egg laying ('ovipositing') starts and eggs and larvae begin to appear on them.
Aggregation sites then have another purpose; they're a place to mate. The female Crow butterflies lay their eggs over widely dispersed sites, and so the winter aggregation can help overcome the mate finding problem.
A large number of Crow butterflies do mate before dispersal but some also mate at male aggregation sites near host plants and plants containing substances used in male pheromones.
A bit more about the Crow
The Common Crow (E. core) belongs to the group of butterflies called Danaines, which are part of the Nymphalidae Family. Both names are from Greek legends. The nymphs were known for their graceful fight. The Danainides are the 50 daughters of the king of Argos, who, all but one, killed their husbands on their wedding night. For this crime they were condemned to endlessly drawing water in sieves from a well.
Many adult danaine caterpillars and butterflies are poisonous. The butterflies also have a slow and heavy flight. Whether the butterflies are named for their flight or their poisons is uncertain.
The Common Crow gets poisonous compounds from the milky sap of some of its main food plants. Many like the oleander can be quite toxic. Two of these are the cardiac glycosides and the pyrrolizidine alkaloids.
The pyrrolizidine alkaloids, also called PAs, are used in the synthesis of male courtship pheromones. Males feed on PA plants at mating times in autumn and spring. They're possibly also used as a bitter tasting defence against birds. Because of this the Common Crow has few vertebrate pests.
The pupa of the Common Crow are shiny metallic silvery gold all over. They're about two centimetres long and are found hanging from the underside of leaves of its food plant.
The eggs are pale yellow coloured and laid singly on the undersides of the young leaves and flower buds of the food plant.
The full grown larva (fifth instar) has alternating bands of orange and black bands edged white all along its body, plus eight black tentacles in pairs. These are on the mesothorax, the metathorax and on abdominal segments two and eight. It can be a garden pest.
Others do it too
The Common Crow isn't alone in overwintering. A number of Australian butterflies use similar strategies to cope with tropical seasons and they can often be seen overwintering together. The Common Crow is often seen overwintering with the Blue Tiger and two other Crow butterflies (E. tulliolus and E. sylvester).
The Blue Tiger (Tirumala hamata) can be found in their millions around Townsville in winter. They are also famous for their migrations inland and southward from the tropics to the subtropics in spring. In autumn the route is reversed and they move northward and toward the coast. Truck drivers always know when the migration is on, as the butterflies often move along roadways and many of them land up on truck windscreens.
The Eurema species (the Grass Yellows from the Pieridae family) also aggregrate in winter but not as spectacularly as the Crow. Euremas form smaller groups in river beds and grass clumps. If disturbed they'll briefly flutter up and then re-settle.
Monarch butterflies (Danaus plexippus plexippus), which arrived in Australia from North America around 1856, only overwinters south of a latitude around the Richmond River in Northern New South Wales. Aggregations have been reported in the Hunter Valley, in gullies along Razorback Ridge near Camden, and even in a park in Earlwood in the inner west of Sydney!
- Australian Butterflies and their Caterpillars
a site maintained by Don Herbison-Evans.
- Macleay Museum
University of Sydney.
- Victorian Butterfly Database
- Butterflies in the Canberra district and their food plants
maintained by the Aranda Primary School.
- Gardening for Butterflies
part of the Society for Growing Australian Plants Australian Plants site
- University of Queensland Insect Collection
- Natural History Museum
- Nature Australia Magazine
- R. L. Kitching, Dr. E. Scheermeyer, R. E. Jones and N. E. Pierce (Eds) CSIRO Publishing, Melbourne, 1999., The Biology of The Australian Butterflies. (In particular:Chapter 8: Pteridae: Lemon Migrant, Catopsilia; Chapter 9: Eurema; Chapter 12: Nymphalidae: Crows and Blue Tiger; Chapter 13: Bush Browns (Satyrinae)
- Elly Scheermeyer, "Overwintering of Three Australian Danaines: Tirumala hamata, Euploea tulliolus tulliolus and Euploea core corinna" in Biology and Conservation of the Monarch Butterfly. Natural History Museum of Los angeles County, Los Angeles Pp 345-354 S. B. Malcolm and M.P. Zalucki (Eds) 1993.
- Kitching, R.L. and Zalucki, M. P., 1981 Observations on the Ecology of Euploea core corinna (Nymphalidae) with special reference to an overwintering population. J. Lepid. Society 35: 106-119.
- R.E.Jones: Reproductive Strategies for the Seasonal Tropics. Insect Sci. Applic. Vol 8 Nos 4/5/6, pp515-521, 1987
- Michael Braby, Butterflies of Australia. by, published by CSIRO Melbourne. This definitive book on Australia butterflies in 2 volumes, and about 1000 pages, is due to be published this month July 2000. It's intended to replace the Butterflies of Australia by I.F.B. Common and D. F. Waterhouse which was published some decades ago.
- Alan Schwenke and Frank F. Jordan. Butterfly Magic: bring back the Birdwing and other butterflies to our backyards. 1992 Earthling Enterprises P.O. Box 5167 West End QLD 4101
- Peter Valentine, Australian Tropical Butterflies. Frith and Frith.
Published 20 July 2000