Do you ever walk by stuff and wonder, “What IS that?” The first time I saw this stuff, that is exactly what I wondered:
At this time of year, they are particularly easy to see because many of the leaves have fallen from the trees… specifically from the Speckled Alder (Alnus incana ssp. rugosa). A shrubby tree that loves wet places, we have plenty of these at Audubon. And somebody loves it!
Wooly Alder Aphids (Paraprociphilus tessellatus) can actually be found on one of two host plants – Alder or Silver Maple. At this time of year, though, you will probably see colonies like this only on Alders. I pulled a few off and put them on the palm of my hand. At the bottom left of the mass, you can see a pretty good image of one critter, legs down, facing toward the right, her back covered with the “wool” that gives her the name.
Her? How do I know it’s a female? Well, I think I’m right on this… though the various accounts I find online don’t always jive with one another.
If I’m I’m comprehending what I read, the wingless ones are always female. They can stay on their Alder host all summer and sometimes even through the winter reproducing parthenogenetically. That means females produce eggs which produce more females, with no male needed for fertilization of the egg. The eggs are held inside the body until they hatch, so young emerge from their mothers live. Look at this cute little girl, also in the palm of my hand:
Now here comes the wild part: When there is an environmental stressor, such as the onset of winter, some eggs will miraculously produce winged individuals that may be either male or female. (OK, there’s probably a scientific explanation… but to me it’s miraculous.) These will fly to Silver Maples where they will mate. Each female will produce one fertilzed egg which will be “glued” to the bark of the tree for overwintering.
Come spring these eggs produce female aphids which find their way to the newly emerging Silver Maple leaves, whose plant juices they eat. They reproduce parthenogenetically building up large numbers of mostly wingless females. Periodically, though, some or all of the offspring manifest wings and fly back to Alders. The generations that live on the Alders don’t target leaves for their meals. Instead, they pierce through the bark on the trunks and branches to access the alder sap.
As if that weren’t fascinating enough, beneath colonies of aphids, you will often find black, sooty spots on the branches. And from these will grow strange, sometimes golden, sometimes black fungi.
These fungi are not attacking the tree – they are purely superficial. They thrive on honeydew – the sweet, concentrated plant sap that is produced by the aphids while they eat.
Which brings us to ants who protect the aphids in exchange for the honeydew… and ladybugs and lacewings that like to eat aphids… and… Oh, what’s that quote about everything’s connected? It’s all so intriguing, isn’t it?