August 11, 2005
The case of the disappearing lady
2005 can rightly be called the year of the PAINTED LADY (Vanessa cardui). I have been regularly commenting on the remarkable numbers being reported throughout the west. On most days, one can go out and easily find them. They prefer to lay eggs on various species of thistle (Cirsium sp.) and it's not difficult to find the caterpillars if you know what to look for.
So my daughter, Michelle, and I decided we would collect a couple of these larvae, feed them thistles, allow them to pupate and then watch them turn into butterflies. They ate thistles, got nice and fat, crawled to the top of the rearing cage and turned into chrysalises. After about 3 weeks, Michelle looked in on the progress and said she thought they'd died. When I looked at the chrysalises, I could see that they were open, but there were no butterflies in the cage....
Where did the Painted Ladies go?
It turns out that being a caterpillar on a thistle is more dangerous than one might imagine. I took a closer look at the dried thistle in the bottom of the rearing cage and found that it was not empty. There were two interesting, and strikingly colored wasps, ichneumon wasps (we still haven't got any farther than family). These wasps lay eggs in the caterpillars, the caterpillars pupate, then the larval wasp feeds on the caterpillar while it's in the chrysalis. It's a metamorphosis is a different sort.
