Monarch Butterflies - a Wanderer's Road Trip
  • Last updated:
  • 26 Apr 2019

One of the most widely recognised butterflies is the large and colourful Monarch, Danaus plexippus, named after two evil characters from Greek mythology. Danaus was the son of an Egyptian king and sired 50 daughters. Balance was maintained when his brother Aegyptus sired 50 sons. Naturally, all 50 cousins paired off and married, then, on their joint wedding night the girls stabbed to death all the boys except one. Plexippus also met an early death in a brawl over a boar’s pelt.

There is no obvious connection between these “nasties” and the beautiful butterfly, native to North America, where it is known for its huge migrations involving millions of individuals trekking south to Mexico and southern California for the Winter, with their offspring heading north again in the Spring.

Over the last few hundred years these very strong flyers, (known as Monarch Butterflies in the US and elsewhere, but for some reason called Wanderers in Australia) have self-introduced in around the 1870s, probably by island-hopping, into the Pacific Islands and Australia. We have seen them in numbers in Fiji and New Zealand (where they pre-date European settlement) and once a swarm of many hundreds in Samoa. 

For an exotic species to become well established here it would require its feed plant, also an exotic, to become established earlier. It is not clear when the major food-source Gomphocarpus physocarpus, family Apocynaceae, was brought in from Africa. These plants are related to Asclepiads which include a few native species. They are commonly known as Milk Weed or still more commonly as Swan Plants. Milk Weed because of the milky sap exuded and Swan Plant because of the shape of the seed capsules. (The botanical name translates to Club fruit Bladder fruit.) These introduced weeds are now wide-spread and often found on scrubby roadsides. In Australia the butterfly is aptly called “Wanderer” and can be found anywhere along a very broad south and East Coast strip although they do not mass-migrate as in the US.

Recently a Monarch/Wanderer landed right in front of us and we thought its life cycle would be good to observe. So the hunt was on for Swan Plants and after a couple of weeks of searching far and wide we found one on the road-side just next to our driveway. We picked some leaves on which were two tiny caterpillars, about 8 mm x 1 mm.

It happened that we had to drive to Sydney at that time so the caterpillars, in a banana box full of Milk Weed, travelled with us. The “fodder” was replenished several times along the way and the larvae munched non-stop. We kept lifting the lid to watch their progress: they were bigger each time we looked. At 11 days (now in Sydney) the striped caterpillars had reached the stage where they climbed to the lid of the box, attached themselves and encased themselves in their jade green, gold-flecked chrysalides (the word is derived from the Greek word for gold).

After a further 14 days each suspended chrysalis turned black and semitransparent and by the next day we could discern folded wings within. Another 2 days and the colourful wings were clearly visible and by next morning each butterflies had completed its metamorphosis. After some minutes allowing the sun to “activate” their wings they abruptly flew off.

Monarchs/Wanderers have large pointed wings allowing them to fly rapidly and soar high in the air, the males aggressively searching for females and for rival males to drive off. They have been recorded covering 130km in a day, flying at 100m or so. Depending on weather, these amazing butterflies have about six to eight weeks to mate, find swan plants and repeat the cycle.

The bright colours of both caterpillars and butterflies serve as warning to predators that their intended prey items carry a strong alkaloid toxin absorbed from the milky sap exuded by their food source, the Milk Weed/Swan Plant.

Monarch eggs hatch in eight days. We estimated that we found “our” pair at two days old. Adding the 27 days “road trip” we established a 37 day term from egg to mature butterfly.

Article and photos provided by Kon Hepers