It turns out, because you have to turn the leaflets over, that hickory trees are potentially loaded with gall mites. There are several dozen hickory gall midge species in the Caryomyia genus, each forcing the tree to make a little shelter for the mite. Acting on a call from a curator on iNaturalist, I examined a few hickories in Green-Wood, which is well-represented with the glorious Carya genus of trees.
In the above pictures, the funnel-like ones are Hickory Smooth Gumdrop Gall Midges. The furry ones… well, there are several furry ones and I’ll need to cut these open to discover what they are.
Hickory Placental Gall Midge. These, like the above examples, were all on pignut (Carya glabra), which seems to be the richest host amongst Green-Wood’s hickories that I’ve seen so far. For instance, on a shagbark right next to this pignut, there were hardly any at all. In addition to pignut and shagbark, other hickories here are mockernut, bitternut, and shellbark. Green-Wood is an island of specimen trees, not a forest, so it’s cool to think these galls have made it here or survived who knows what.
Here’s some of the furry-spiky ones, on mockernut this time.
Cutting one open reveals to the iNaturalist curator that this is Purple Gumdrop Gall Midge.
Caryomyia marginata, no common name, on the same mockernut.
That’s so cool (in contrast to the heat outside) All those tiny strange habitats, what is the world like for those little critters?! I doubt that they will find anything nearly as amazing on the Mars explorer mission.