Extending the feeding season

Poplar leaves with green spots from Ectoedemia larvae

One of my primary reasons for starting up this blog, nearly three years ago, was that it would encourage me to learn new things about the world around me. And so it has. Most of the time it’s through my discovery of something interesting or unusual that I come across while out hiking (or sometimes it comes to me), and which I then look up more info on once I get home.

Recently, I was approached about whether I might be interested in slightly revising my book review of Tracks & Sign of Insects, which I’d posted here on the blog back in May, for inclusion in a Vermont-based magazine called Northern Woodlands. The magazine is an interesting mix of articles, somewhere at the meeting place of forest “management”, forest exploitation, and forest appreciation. I admit to being a bit of a purist – the thought that some people feel the need to “manage” their forests in order to make their forests “healthier” really bothers me, and while I recognize the need for lumber and tree harvesting (and even don’t mind most forestry practices, to some degree), it still hurts my heart a bit to see a forest put to that use.

So when I got my copy of the magazine in the mail, I skimmed over all those articles. There are still quite a number that fall into the “appreciation” category, however, and more than once I found myself thinking, I didn’t know that, that’s so neat!

Poplar leaves with green spots from Ectoedemia larvae

One such article was relatively fresh in my mind while I was out walking our own woods a couple of days ago. We don’t have very much woods, or at least not walkable woods, here on our 30-acre parcel (most of it is down the road at the 100-acre bit). Much of what occurs here is wet, especially at this time of year. There’s a small patch near the back which I sometimes cut back through and then wander along the strip of forest at the edge of the property (actually just the edge of a larger expanse of woods, but the fence of the property line runs through it and only a little bit bleeds over from the neighbour’s land onto our own).

I was watching my step as I came around through the trees, making sure I didn’t trip over anything, when I spotted these leaves. A month ago, before I’d received the magazine, not only would not have known what was going on here but I probably wouldn’t have even noticed them in the first place, mixed in with the rest of the fallen leaves (see top photo). But there’d been a short half-page article on them in the magazine, and so stopped and gathered a bunch together so I could take a photo to share with you guys here on the blog.

Poplar leaves with green spots from Ectoedemia larvae

You’ll have noticed that they’re all poplar leaves, and that all of the leaves seem to have one section of the leaf, in most cases between the first and second major diagonal veins, which has remained green. A closer inspection reveals a small blemish at the base of this green strip, butted up against the mid-rib and the lower vein. If you examine this under magnification (some folks carry pocket loupes in the field with them, but if you lack one you can flip your binoculars upside down and look through the wrong end, holding the object a centimeter / half inch away from the lens, to the same effect) you’ll see a little worm tucked in the blemish.

The worm is a caterpillar of a moth in the genus Ectoedemia. It’s just a little moth, less than a centimeter/half inch long, with long, narrow, blue-gray wings and a fluffy orange head. The caterpillars are late feeders – perhaps a strategy to avoid the predation pressure of breeding birds searching for food for their young? – feeding on the leaves well into the fall. So late, in fact, that the leaves drop from the trees while the caterpillars are still munching on them. It does the caterpillar no good to be chewing on a dead leaf, so it ends up secreting a type of plant hormone that keeps the leaf alive for a while longer. The article doesn’t specify, but I suspect that, given this strategy, the caterpillars cocoon within the fallen leaves and then pupate and emerge as adults in the spring.

Ectoedemia sp?
I think this might be an Ectoedemia sp. Or it might not be. Those little micros are so hard to ID. (Also hard to photograph well, but that's a different problem.) But if it's not, well, the Ectoedemia sp. adults look an awful lot like this, anyway.