17 May 2010

Macro Monday-A Milkweed Story

I had hoped to share with you today some pictures of my favorite behavior.  While at Huntley Meadows Park this weekend I found several instances of ants "farming" aphids on purple milkweed (Asclepias purpurascens) plants.  Alas, due to lighting conditions, the position of the aphids, the wind, and the inherent difficulties of working at greater than life size magnification, I was unable to get any successful images this weekend.  Despite spending several hours trying to get a successful image, upon reviewing the few hopefuls after download, not one of them is good enough to even bother sharing.  Rest assured I will return and try to photograph this behavior again.  The short story is that the aphids are feeding on the phloem of the plant in such quantities that they can't process it all and the mostly undigested sap comes out of the alimentary canal of the aphid as "honeydew".  The ants stroke the aphids with their antennae to "milk" the honeydew from the aphids.  The ants will often "farm" the aphid colony, protecting it from predators.  Some ants even go so far as to collect and store aphid eggs in their nests over the winter and then carry the newly hatched aphids to the plants in the spring.

In place of those images, I'll leave you with two successful ones.  First, an image of one of the aphids' main predators, the multicolored Asian lady beetle (Harmonia axyridis), pictured here on a purple milkweed leaf.  This introduced species has established itself relatively recently across much of the US after its release as a biocontrol agent of aphids and scale insects.  While successful in preventing much agricultural damage due to these pests, it is now considered by many to be a nuisance species itself, due to its habit of hibernating in large numbers in houses and its ability to outcompete native insect predators.

The next image is of the buds of the purple milkweed itself.  Most of the plants at Huntley are still have very young green flower buds.  However, a few plants in sunny locations like this one, are beginning to show their red and purple color.


  1. Great post - must be neat watching aphid farming, i have never observed. Also can't remember if you had seen the link i tweeted but with ladybugs - check out: http://www.lostladybug.org/ to report ladybug sightings.

    dan (docforestal)

  2. I LOVE ladybugs!! And I LOVE milkweed!! Great post!

  3. Thanks for the kind comments Dan and Kerri. Dan I hadn't seen that link, thank you. Perhaps my daughter and I can go out on a ladybug hunt sometime soon, she would love that!

  4. Love the symmetry of the milkweed shot.