Backyard Nature: An ecosystem in the trees

by Marlene Berlin

I recently discovered a new ecosystem up in my trees – by looking down.

That black stuff isn’t dirt.

I returned from vacation to find a sticky black substance on my backyard deck. Above was a crepe myrtle I’d had planted in the spring. I looked up to find many leaves covered by the same black substance. Then I saw the white spots in the tree. And one of them started to move.

I suspected immediately that they were aphids, because some years back, the insects’ secretions coated my back windows and deck with a sugar-rich, sticky substance called honeydew. Soon after that, black sooty mold was sprouting on my deck.

Back then, I called Bill Eck at Bartlett Tree Experts, and he found an aphid infestation in my giant oaks. He suggested a systemic insecticide treatment that would kill the insects. I concurred, and there were no more blurry windows from their droppings for the next few years.

While I pondered the problem this time, I noticed several flying insects buzzing around and alighting upon the tree. Were they feeding on the aphids? I had been reading The Arbornaut by Meg Loman, a biologist and botanist who climbs into the tree canopies of forests around the world. This, she calls the eighth unexplored continent. Loman’s explorations have revealed ecosystems populated by bugs, birds, mammals, and other plant life. The trees’ leaves provide food for some insects, which in turn are food for other insects and birds. This gave me an idea.

Many insects find aphids delectable, including ladybugs, which I ordered online. I spread them around the tree hoping that they would have a feast. Yellowjackets and long-legged flies, which I have seen in the tree, also enjoy eating aphids.

So do the goldfinches that visit my birdfeeder. They’ve been been pecking around in the tree, too.

Some aphid insect predators are parasitic, laying their eggs on or inside the bugs. The larvae that hatch from the eggs then feed on their hosts as they grow.

Aphids also have allies. I have also seen ants crawling in the tree. They are attracted to the honeydew, and in exchange for the sugary stuff, they defend the aphids from insect attackers.

An ant receives honeydew from an aphid. (photo by Dawidi, Johannesburg, South Africa via Wikimedia Commons, CC BY 2.5)

So this time, I am getting great enjoyment from watching this new ecosystem develop. I just hope the beneficial bugs and goldfinches will prevent the aphids from harming the tree.