The leaf miner is the larva of a fly, moth, sawfly or beetle that tunnels its way, by eating, through a leaf. It’s amazing that many species have come up with this means of survival: to live and eat in the space between the upper and lower layers of leaves. The track of the larva gets wider as its life progresses and its body grows. It graphs its own life story right onto its home/food source.
It’s funny to google a creature like this and find mostly information about how to kill it. I think leaf miners are one of the quiet miracles of life on earth–the patterns of their tracks can actually be used to identify them by species. Because they also damage crops and trees, we’ve invented ways to wipe them out.
Meanwhile, plants themselves have a subtler strategy: The variegated colors on some leaves might be an attempt to fool leaf miners, as the leaves appear to have already been mined.