Poplar Leaf Gall in pen and ink

This week's Illustration Friday prompt is mysterious. I know that I almost always start by saying "this is a quick doodle of..." or something like that, but this time it really was a quick doodle since I was in the middle of doing something for work and realised that it might do for mysterious.

As I've mentioned more than a few times, I work at a nature centre that sits at the entrance to a sanctuary. Every year, the balsam poplar trees in the sanctuary get leaf galls something like the one I've drawn here, and every year the kids ask about them.

And every year?

I get stuck once I get past "they're made by insects." I mean, I know why the insects make them and I can always lead the conversation to protection from predators and metamorphosis and things like that, but if someone ever wants to know specifically what kind of insect is living in the gall, I'm stumped.

I suppose a person could always cut open a gall and see what she finds, but somehow it doesn't seem like it would help the message of the importance of all life to a system to randomly decide that this particular creature's life should be sacrificed for curiosity's sake.

I should say here that no, I'm not that much of an extremist when it comes to protecting nature. I swat mosquitoes like everyone else. I'm just saying that it's not a great image for the kids to cut open a gall and find two halves of a larva...

Anyway. I had a bit of time today so I decided to bring in a leaf ( a bit worse the wear already, but autumn comes pretty early here) and see if I could make any headway into this mystery.

I learned something.

I learned that it's massively difficult to read scientific papers about agricultural and horticultural pests when you trained as a mammalogist and not an entomologist.

I also learned that our mystery gall is probably caused by (drumroll please...) an aphid. What used to be called a gall louse. And that there would be tons of them (well, not literally) living in this one single gall.

For the complete nerds among you, it may be one of the Pemphigus aphids. The actual species? Well, that'll have to remain mysterious. There's no way in heck I'm taking a crash course in aphid morphology just to find a species name. I've been triumphant about one mystery today, and I think that'll do me.