Look closely at the leaves of slippery elm (= red elm) (Ulmus rubra); you may be lucky enough to spot the unusual looking elm cockscomb galls produced by the so-called elm cockscomb aphid, Colopha ulmicola. Although these galls are commonly mentioned in the literature, I've rarely seen them in southwest Ohio where elm sack galls produced by the aphid, Tetraneura ulmi, are the dominant aphid gall found on slippery elm.
Early cockscomb galls are tubular-shaped, almost worm-like, and light green. As they mature, the galls will take-on the appearance of their descriptive common name: they will look like bright red chicken cockscombs rising up from elm leaves. It's a strange sight.