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.
The orange-yellow oleander aphids (
Aphis nerii)
are common on these plants. A week ago, when many of these photos were
taken, the aphids covered about 2-3" of the top of every shoot. This
week their numbers are much reduced, with just a few hardy individuals
remaining where hundreds dined last week. This is at least the second
rise and fall of aphid numbers on my plants this summer. I'm sure they
will go through at least one more population cycle up and down before
frost comes this autumn.
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....
Each
milkweed shoot with its covering of yellow aphids near the tip seems to
also have at least one or more of these blobs of gray and white
protoplasm which, I am pretty sure, are actually syrphid fly larvae.
Although the blobs are stationary when I usually see them, I have
occasionally seen one "hightailing" it from one area to another.
Looking on BugGuide.net, this looks like the larva of
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.
Less
common, but still easy to find, are these little bumpy caterpillar-like
animals that are also, I believe, syrphid fly larvae. I've not been
able to figure out which species or even genus these guys belong to, but
I do find it fascinating that two different species of syrphid flies
are munching on my oleander aphids! The only way to really tell for
certain would be to raise up some of these larvae to adulthood, which
sounds like a fun project when the boys get a little older.
If you ever see a piece of trash seeming to move on your plant, look a little more closely....
You
may be seeing a green lacewing larva, which hides under a pile of
debris that includes its castoff skins from earlier molts.
If you look closely in the photo above, you can easily see the yellow oleander aphid being eaten...by the actual lacewing larva at the bottom of the pile of debris. Lacewings are fierce aphid predators as both larvae and adults.
Not
uncommonly among my aphid populations, I will see a dark brown aphid
that doesn't move. This is an aphid mummy. Tiny parasitic wasps lay an
egg in an individual aphid and the developing wasp larva eats out the
insides of the aphid, leaving the aphid a literal shell of itself. Only
one baby wasp per aphid, but each female wasp can then go on to lay
eggs in many aphids, so aphid mummies are welcome sights on my milkweed
plants.
There are other more generalist predators that I'm seeing around my milkweeds, too, which may or may not be preying on the aphids.
I often see tiny, longlegged flies, for example, flying around and landing on milkweed leaves for short periods of time.
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
something!
Clad in the red-orange and black colors of the classic milkweed insect,
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.
The
final predator I've been consistently seeing around my milkweeds in
recent weeks is a damselfly. Again, I don't know if this dainty
creature is eating winged aphids or not, but I doubt it would turn one
down.
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!
