Leaf Miner

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When I first thought of leaf miners I was really only looking at the tracks they make and not much about the insect itself. But after reading and doing more research I found out the term leaf miner is used to refer to any species of insect whose larva spends part or all of its life between the epidermal or outer layers of a leaf. It’s like a little cave inside the leaf that the caterpillar creates for itself to hide and feed. They can also be found in fruit, grass, aquatic plants and stems.

Usually I photograph things while I’m on my walk and then learn about them later. This time was just the opposite, after reading about leaf miners for a couple of weeks, I left work early last Friday and stopped by Shenandoah River on my way home. I was amazed that I was seeing so much miner activity and recognizing leaf damage and characteristics that would have gone unnoticed before. These photos were taken within a few yards of each other. I also collected some to photograph through my microscope at home, but you can easily see these things with the naked eye or a hand magnifier.

As they feed they mine tunnels of various patterns -- this is what first caught my attention. A leaf mine can be used to identify its creator by the size, pattern and location of the mine. I find the Serpentine leaf miners are the most interesting as they wind and feed along in snake-like pattern across the leaf, some gradually widening as the larva grows. The most common are the blotch leaf mines created when the larva turns around and around during feeding. The shape can be irregular or in a circle or oval. One subgroup is the tentiform which looks like a bulging blotch-type mine. Sometimes you can find a combo serpentine ending in a blotch. In Insect Life and Insect Natural History, S.W. Frost states, “They write their signatures in the leaves, a habit which greatly assists in determining the species.” I would love to find such an identification key.

Leaf mining is not restricted to one group of insects but is used by the larva of Lepidoptera (moths), Coleoptera (beetles), Hymenoptera (sawflies) and Diptera (flies). Leaf miners generally begin their life with when eggs are laid in or on a specific host plant. Most spend their entire larval stage within the leaf while some will cut their way out and finish their life cycle outside the leaf.

You can hold up a left to the sun and often see the larva inside. Look in the light brown area where all the chlorophyll has been eaten.

The larva is tiny and flattened as compared to a butterfly caterpillar. They don’t have legs and their chomper mouth parts are projected forward to make it easier to feed their way between the top and bottom layers of the leaf.

I watched this one through my microscope as it was feeding. It was swaying side to side as it ate, just under the outer layer of the leaf.

The beetle leaf miner eggs are generally laid on the surface of the leaf and often covered with a shiny black coat. When they hatch the baby larvae bore into the leaf.

You can see the hole where this larva began its journey.

Most of the time the beetle leaf miners pupate within the mine, in the circular or oval cocoon, then they cut a small round disc from the leaf and fall to the ground to later emerge.

Sawfly leaf miners are almost always the blotch types and the eggs are laid into the leaf tissue.

The black doted stuff is fecal material.

The Lepidoptera (moth) leaf miners are the largest group and use a large combination of strategies for their mines including tentiform.

Leaf miners are very interesting any can be found most forested areas. I encourage you to go outside and look for some. You will be amazed at the variety of squiggly lines you can find.

Learn more one other ABC Wednesday blogs.