Tuesday, May 22, 2012

Spider Milkweed and Caterpillar

Spider Milkweed is putting on a wonderful show this year at Blue Jay Barrens.  This is a spring blooming species that is usually well past flowering by the time summer arrives.  I thoroughly enjoy this plant.

The flowers are jumbo sized compared to other milkweed species, but seem to be the least attractive to butterflies.  The most frequent flower visitors are ants.  These small black ants are in every flower I check.

Blue Jay Barrens is at the extreme northern limit of the Spider Milkweed’s range.  This is a southern species, so I imagine cold winter temperatures are one of the factors controlling its northward expansion. 

The plants are generally long lived.  I’ve got a couple of clumps that have been around for at least 15 years.  Occasionally a plant will fail to return in the spring. On average, the number of plants continues to increase, so I’m fairly confident that Spider Milkweeds will remain a permanent resident.

I have populations of Spider Milkweed at three locations.  One is growing in dry ground on a hill top, the second is in dry, rocky ground on the upper slopes of a steep hillside and the third is in wetter soil near the base of a hill.  That tells me that the plant should thrive in any of the open areas found here.  Up until last year, I had six Spider Milkweeds growing in my Prairie Garden, but Allegheny Mound Ants moved in and chewed the plants to the ground.  I don’t know why this happened, but it makes me wonder if the ants will allow this plant to grow near their mounds.  There are currently no mounds near any of my existing Spider Milkweed populations.

All of the populations contain a few younger plants.  It typically takes several years before the plant is old enough to flower and then a couple years of small flower heads before producing the display shown in my first photo.  All of my plants of this species show a bit of a lean.  Young plants especially may grow in an almost horizontal position.

Last year, this plant hosted a batch of caterpillars of the Unexpected Tiger Moth, Cycnia inopinatus, which I photographed, but didn’t identify until they had disappeared.  I was quite excited when I discovered this to be an endangered species in Ohio.  The larvae begin feeding on the flowers and then progress to the leaves.  I found some signs of flower feeding, but could see no larvae.

I was luckier when I checked a plant in another population.  This cluster of flowers was full of larvae, at least three of which are visible in this photo. 

The larva host plant is growing on the hill behind the house, so it is in a convenient place for me to frequently check.  Hopefully, I’ll be able to follow the progress as these larvae develop.


  1. I thought you had quit blogging, but am really please to see it's not so. So, welcome back (to me, since it appears you were not away for long at all.)
    The little ant is Monomorium minimum, one of the few ants of whose diet flower nectar seems to be an important component.

  2. Thanks Lois.

    Hi James. A special person requested that I continue the blog, so I have returned. Thanks for the ant ID. I got out my copy of Ants of Ohio and read up on this species.

  3. Great close-up shots. Are these the caterpillars called 'woolly bears'? I didn't know they were endangered.

  4. Thanks Pat. The common black and orange Woolly Bear is the larva of the Isabella Tiger Moth, a different species than what I show here. The caterpillars on the milkweed are of the Unexpected Tiger Moth. To see more advanced shots of the caterpillars go here http://bluejaybarrens.blogspot.com/2011/09/unexpected-tiger-moth.html