Home sweet home

Inside a leaf, an insect can gain food and shelter simultaneously.  The challenge is that leaves are nearly flat.  It seems like it should be very difficult for insects to live inside them -- at least not without making a gall.  Yet, the larvae of numerous species of moths, flies and other insects have overcome this challenge.

These larvae are known as 'leaf miners' and they leave distinctive marks on the leaves they inhabit.  Some leaf miners take long, winding paths through their leaves.  The resulting 'serpentine' trails are often filled with the frass (droppings) of the larvae, which turns the trails black behind the leaf miners.  To me, this seems like a big drawback of living inside your food.

The trail left in a rose leaf by a leaf miner, possibly a larva of the moth Stigmella rosaefoliella.

Other leaf miners consume large patches of leaves, creating opaque 'windows'.  Sometimes, as in the picture below, the leaf miner can be seen through the window.

A leaf miner is visible through a 'window' in a common morning glory (Ipomoea purpurea) leaf.

To get a better look at the leaf miner pictured above, I flipped the leaf over.  I found that this morning-glory leaf miner (Bedellia somnulentella) was keeping its feeding area clean by expelling its frass through a hole in the leaf surface.  It would seem that, in the case of leaf miners, outdoor plumbing is the significant innovation.

A morning-glory leaf miner (Bedellia somnulentella) in a common morning glory (Ipomoea purpurea) leaf.