I was walking around in a cemetery with a friend who spotted these strange balls on staghorn sumac leaves:
I figured they were a galls, which are swellings in plants caused by parasitic fungi, bacteria, nematodes, or in most cases, insects and mites. It’s always fun to crack open galls to find out what is living inside. These turned out to be full of aphids! I wasn’t expecting that.
When I got home I found out that these are sumac gall aphids (Melaphis rhois). Like all galling parasites they have a very clever trick. Through some highly specialized chemical secretions or physical modification they force their host plant to grow their food and shelter for them. It’s a pretty sweet deal for the aphids. These galls start when a female aphid lays a single egg in a sumac leaf, when it hatches the gall starts forming and that single aphid reproduces asexually within the gall. So all the aphids within the gall are identical clones of one another.
But it gets trickier. Later in the year winged females fly off to start a new colony on moss. This radical host switching behavior has been happening for over 48 millions years and is one of the longest lasting plant-insect relationships ever documented. At some point the clonal colonies on moss produce males and females which mate and it’s these mated females that fly off to lay eggs in the spring.
As species have evolved and gone extinct and the continents have shifted, these aphids have been in an annual three-way dance with trees and mosses which gave them all the food and shelter they needed. Only recently a precocious bipedal primate showed up who found their own ways to get plants to produce food and housing for them. They’re pretty clever too but they have a tendency to destroy all their prefered habitats. We’ll see if they can keep it up for 48 millions years.