My milkweeds are hopping these days. Sadly, I've only seen one monarch caterpillar, but I am still fascinated by all the insect life that I am seeing. Most of my observations have been on tropical milkweed (Asclepias curassavica) simply because I have several big, healthy plants in pots on my back patio and they are easy to check on and photograph, but I'm fairly certain that what I'm seeing isn't unusual for other milkweed species.
So what's keeping the aphid
populations from exploding out of control? If you look closely at the
photo above, you can begin to see the answer. Specifically, here are
some of the candidates I've been seeing....
the syrphid fly, Ocyptamus fuscipennis.
I have certainly noticed syrphid flies that look like these adults
hovering around the aphid clusters. There is no common name for this
little fly that I know of, but the BugGuide link will allow you to see
what the adult looks like, so that you can notice if your milkweed
aphids are attracting attention from this species, too.
If you ever see a piece of trash seeming to move on your plant, look a little more closely....
There are other more generalist predators that I'm seeing around my milkweeds, too, which may or may not be preying on the aphids.
Longlegged flies (Family Dolichopodidae)
are iridescent green or brown and are known to be predators in both the
larval and adult forms. Although I have never seen one pay attention
to, let alone eat, an aphid, I can still hope. They've got to be eating
milkweed assassin bugs (Zelus longipes)
are another generalist predator that I see these days, both on
milkweeds and on other plants around the yard. I see the milkweed
assassin bugs hunting up and down the plants, sometimes hanging out in
the flowers, but just as commonly walking up and down the stems or
inspecting both sides of each leaf. Their eyesight is superb and it can
be hard to sneak up on one to take its picture. At first it will
simply duck to the other side of a stem or leaf or flower cluster, but
if you persist, it will readily fly away.
So, as you look at the aphids on your milkweeds
in horror and dismay, look a little closer - there's a good chance
you'll see some other, interesting insects drawn in to the feast that
they represent in the animal world!