5 September 2021

Have you seen an unusual white squiggle on a green leaf? The pattern was made by a leaf miner, a tiny insect larva that eats a path between the top and bottom surfaces of the leaf.  The path ends when the larva is ready to pupate. When the insect departs it leaves a hole.

There are many tiny moths, beetles, sawflies and flies that make leaf mines. Some create blotches. Others, like this one, make serpentine paths. You can identify the insect(s) that made the paths — or at least narrow the number of species — by noting the type of mine and identifying the plant host.

This serpentine leaf mine was on white snakeroot (Ageratina altissima) in Frick Park on 19 August. Based on the Illinois Wildflowers list of insects that feed on Ageratina altissima, here are two possible suspects that create serpentine leaf mines and live in Pennsylvania.

• The larvae of a tiny fly, Liriomyza eupatoriella. (NOTE: While researching this insect I discovered Charley Eiseman, an expert on leafminers and author of the only photo of the bug at bugguide.net. More on Charley Eiseman below.)

• The larvae of a tiny moth, Leucospilapteryx venustella.

If you want to know more about leaf miners, go to the expert. Check out Charley Eiseman‘s book, Leafminers of North America or visit his BugTracks blog where he writes about all kinds of insects. He’s even discovered new species.

(photos by Kate St. John, screenshot of bugguide.net and photo from Wikimedia Commons)