Tuesday, 29 August 2006

They call them the wanderers

Millions of monarch butterflies (Danaus plexippus) are about to begin their mass migration from southern Canada and the northern United States to their wintering grounds in California and Mexico.

Although native to continental America, monarchs have spread far from home. They are widely distributed in Hawaii (where a black and white form occurs on the Big Island) and Guam. Stragglers were apparently reported from eastern Australia as early as 1856. They were well established by 1878, when this drawing was made of a caterpillar in Tasmania.

The caterpillars feed on poisonous milkweed (Asclepias), cotton-bush and swan plant (Gomphocarpus), all of which have been introduced to Australia. They are undeterred by the plants' toxins. So undeterred that they store them to use for their own defence. To warn potential predators of the danger, the caterpillars sport vivid aposematic coloration.

Making a meal of poisonous weeds stands them in good stead. They keep the toxins through metamorphosis into the adult stage.

With their prodigious powers of flight, wanderers have dispersed across Australia. Their dependence on introduced plants has restricted their establishment in many areas but as the weeds spread, so do they. Although spectacular, the butterflies are signalling the decline in our natural environment.


tapperboy said...

Worth waiting up for, 10:59pm here at the moment :)

I've grown up with these guys my entire life. I'd known they were from over there *points* from a very early age but only recently realised they were never an aussie native beast.

I do love their chromelike looking chrysalides though. Probably not environmentally pc to but from an arty perspective permissable. Least I grant myself express permission to like em :)

David Nelson said...

Yes, it is late, early start tomorrow too, but I couldn't resist a reply:


Anonymous said...

Like davidavid, we see only a rare one each year, except when high percentile winter rainfall lets the hosts get away in weedy ground.

We're in irrigated milk and beef pasture/ mixed horticulture area in the Southwest.

So this year, after an exceptionally wet last year I'm unable to go into town without noticing one in yards or on roadsides.

With the davidavid snap, I like this one for a carnival of the spineless entry. Short and sweet.


Sherryl said...

I grew up with monarch butterflies in NZ, and wrote a poem about the huge migration in the US a while ago. I was surprised to find, on a trip back to NZ in March, that monarchs are considered endangered over there now. Well, I shouldn't have been surprised really, considering how many other species humans have killed off. But there has been a concerted effort to assist the monarchs to make a comeback, principally by asking people to grow swan grass in their gardens to provide food. And then to protect the cocoons. I gather it's the destruction of food that has led to their reduction in numbers. It was great to see the 'average person' growing stuff to help a beautiful butterfly. (No, I'm not a scientist of any kind!)