Leafmines and their miners are a subject I started to look at last summer but I quickly discovered that, in order to identify the miner, you had to know the plant they were mining, so I needed to improve my botanical knowledge before I could go much further. That effort has begun, and is ongoing, so I will start to look again at the miners in the coming months.
Firstly though, in case you don’t know, leafmines are made by the larvae of various insects. The mines are their homes and their larders – as well as providing them with some degree of protection from predators, the larvae eat the tissue of the leaves they live within, thus creating their mines. The larvae can be the immature stages of various species of flies, sawflies or moths, and, apparently, some beetles also mine leaves.
If you look at a mine, you will often see a tiny hole at one end, which means the creature that made it has left the premises, to pupate or to being life as an adult. Sometimes, you can still see the larva within, and you can often also see the pooh (known as frass) it has left behind as it eats and tunnels.
The shapes of the mines can vary considerably, from long meandering or straight lines to roundish blotches, and these shapes, plus the placement of the mine within the leaf (some occupy just the upper or lower surface, some go right through) and the identity of the plant, are the main ways to determine which creature has made the mine.
**p.s. Since posting this, I’ve been told what I thought was a leaf mine on ivy (the photo on the right in the middle) is actually caused by a fungus, possibly Phoma hedericola, the most common leaf spot of ivy. I can see these leafmines are going to be even more tricky than I anticipated!