Leaf Rollers

I have long been interested in leaf rollers but could never find good information about their lives; at least not what I thought was good. Mostly what I found was how to destroy and wipe them from the face of the earth. However, I recently bought a very old book written in 1942 by S. W. Frost, titled “Insect Life and Insect Natural History”. I immediately turned to the chapter on Leaf Rollers.

Below is a series of photos I took this summer of a fine example of a leaf roller. I did not open it up because I didn’t want to disturb such a skilled craftsman as this little caterpillar obviously was. There are lots of leaves that look like leaf rolls but a true leaf roll is made by a larva that uses silk to twist or distort the leaf into a roll. Frost states that, “Many insects utilize rolled or curled leaves but few “roll their own.”

It is the method of leaf rolling that I find so fascinating. I tried to imagine a tiny caterpillar grabbing the edge of the leaf by it’s tiny prolegs then rolling over and over until it was all rolled up in a snug little leaf but that method just didn’t make any sense at all. So here is the account that Frost gives. “The chief qualification of a leaf roller is the ability to spin an abundance of silk, for this is the mechanism by which the leaf is manipulated. Threads of silk are spun across the portion of the leaf to be folded or rolled. If the rolls is to be lengthwise, the strands of the silk are spun perpendicular to the midrib of the leaf; if the roll is to be crosswise, the strands of silk are spun parallel to it. As the strands of silk dry, they shrink and pull the edges of the leaf inward. New and shorter strands are then spun which in turn shrink and pull the edges of the leaf closer together. This is continued until the edge of the leaf is drawn completely over and is fastened with other strands of silk. Apparaantly the larvae do not use pressure to cause the leaf to curl but at times the growth or expansion of the leaf may assist the larve in their operations. The leaf is sometimes cut and a small flap rolled into a cone.”

So there you have it and I hope you are as impressed as I am. Aparantely the larva is on the outside of the roll, like I am when I roll up a sleeping bag. Imagine using elastic tread secured to the end of the bag and then sewing it a few inches forward and letting go. It automatically rolls up. Then you attach more elastic tread, repeating this over and over until you have it all rolled up.

You can see some of the silk strands attaching the outside of the leaf to the inside and how that would pull together as it shrunk.

The roll then can be used as a shelter and eaten from within. Some use them as a safe place for pupations to take place. Others may poke out their heads to feed on other leaves or fruit near by. Once abandoned they are often used by other insects and spiders. I have found spiders in a lot of the ones I have unrolled in the fall. So when you are out looking at fall leaves see if you can spot a rolled leaf or a folded leaf. You will also see tunnel tracks in some leaves; those are leaf minners and I will talk about them next week.

See more exciting photos and commentary at ABC Wednesday.