Milkweeds and Monarchs

This afternoon, as I was leaving Carrington Falls Reserve (part of the Budderoo National Park) I noticed an unfamiliar white flower growing beside the road.

Gomphocarpus fruticosus Narrow-leaved Cotton Bush

Naturally I stopped to have a closer look. I realised from the shape of the flowers that it was probably in the Milkweed group. That was easily verified by tearing a single leaf. White sticky sap emerged immediately.

Gomphocarpus fruticosus Narrow-leaved Cotton Bush

I recognised that this plant, whatever it might be (and I did not know for sure, at this stage) was both a terrible weed and the preferred host plant for caterpillar of the the Monarch Butterfly. Sure enough, you can see a caterpillar of that species of Butterfly feeding on the plant, just underneath this head of white flowers. It has striking yellow and black bands across its body. It is just visible in the lower section of that image.

Gomphocarpus fruticosus Narrow-leaved Cotton Bush

Seed Capsule forming, It gives the plant its name of "Swan Plant"

I ought have recognised this plant immediately, for my Mother, having been a keen Floral Art enthusiast, often used the seed pods of the Swan Plant in her flower arrangements. But that was in Melbourne, when I was a child. When we lived in Canberra, that plant was not available, as the climate is too cold for it to grow there.
The seeds earn the plant the other name of Narrow-leaved Cotton Bush, for they have a structure attached to the hard seed which is made up of silky filaments, which allow the seed to be carried freely on the wind. And that is how it manages to be such a weedy plant. The plant is also toxic to stock, which makes it a pest for agriculturalists and livestock farmers.

The black and yellow colours of this caterpillar are distinctive.

Black and yellow seem to be universal warning colours in Nature.

Add to that the two pairs of dangerous looking (but harmless)

black "tentacles" which the caterpillar waves around

and I was persuaded not to interfere with it.

Those warning signals seem to keep birds away.

Caterpillar of Monarch Butterfly - Danaus plexippus

This caterpillar is the larval stage of what is arguably the most famous Butterfly in the world - the Monarch Butterfly. The Caterpillar feeds on various plants (including this one) that have a poisonous milky sap. The Caterpillar appears to retain the poisons in its body making it unpalatable to predators. The Monarch Butterfly's orange colour is a warning for predators to stay away, as the chemicals they got (as caterpillars) from feeding on milkweed plants makes the butterflies poisonous. Source Don Herbison-Evans website
This plant is in the family Apocynaceae, many of which produce strong chemicals, some of which are used medicinally, Many plants in this family are toxic to animals, including humans


The Butterfly of this caterpillar is famous for its migrations in North America. You can click to see a clip from a BBC documentary about that migration here.

The Caterpillar of the Monarch Butterfly "develops two pairs of black tentacles protruding from its back: a long pair on its mesothorax, and a shorter pair on its eighth abdominal segment. These tentacles are soft and in no way dangerous." Source Don Herbison-Evans website.

Caterpillar of Monarch Butterfly - Danaus plexippus

Caterpillar of Monarch Butterfly - Danaus plexippus

I met a friend while I was photographing the flowers and these Caterpillars, and I explained to her that I found myself with a moral dilemma. I wanted to destroy the plant because it is a Weed, (and particularly because it is growing within a National Park), but I did not want to kill the Caterpillars. We talked about this and we agreed to take off all flowers from the plant, and to destroy the several seed pods which were just developing, by crushing them on the road. The seeds were not nearly enough developed to be viable.