Asclepias speciosa ‘Davis’. From High Country Gardens. This is the only milkweed I grow on which I’ve actually seen a monarch caterpillar. I just planted this last year, and voila, my first caterpillar! They sure do make a mess! But that’s alright as it makes my heart sing to see a monarch.
You may be wondering how such a brightly colored caterpillar avoids being eaten by birds, as this caterpillar was feasting in broad open daylight. The trick is that the monarch’s peculiar coloration sends a clear signal to potential predators to avoid eating it. That is, birds evolved to instinctively avoid this caterpillar, as it is highly toxic to them. The caterpillar becomes toxic by ingesting the poisons in the milkweed, which accumulate in its body. The monarch caterpillar is itself immune to the milkweed’s poison, of course.
I started putting milkweed in my gardens two years ago, starting with Asclepias verticillata (from Bluestone Perennials) and Asclepias incarnata (from High Country Gardens). This spring I started yanking out the verticillata, as it was spreading aggressively. I also read that it’s very toxic, and I was worried about it spreading to the lawn, where a rabbit might accidentally ingest it. The incarnata doesn’t spread, but it’s a larger plant than I anticipated — almost 4 feet tall — and too large for the space where I currently have it, so I plan to move it this spring. It’s an attractive plant, though not the monarch magnet that I was hoping.
I just ordered two more ‘Davis’ milkweeds from Annie’s Annuals.
It’s erroneous to think that gardening is a trivial hobby, as we are the ambassadors for the natural world. Can you imagine a world without butterflies? The butterflies and other insects are dying off in alarming numbers. That’s distressing in itself, but disappearing insects also means disappearing birds, as insects are the most important part of many birds’ diets.
Update (May 9, 2019): Today I noticed a shoot of Asclepias speciosa appearing about 18″ from the original plant, which was just planted last year. So it’s already starting to spread. I don’t mind, as I purposefully planted this milkweed in a spot where I want it to naturalize. However, it does make me realize that it was probably redundant to add the two additional plants this year.