Caterpillar Migration

Moves straight- not a snake

Nancy Schanda sent me this video of a migration across her walking path in Forsyth, high above Lake Taneycomo.  There were several of these slow moving, snake-like columns which almost have a wave like appearance on close viewing.  Her accompanying pictures show it was made up of a mass of tiny caterpillars piled deep on one another.  This phenomenon was new to both of us.

The Eastern tent caterpillars and forest tent caterpillars will move in mass from one tree to another, but I hadn't seen pictures showing them bunched together in an organized fashion.   

Pine processionary caterpillars travel in a line, nose to tail, as seen in this video.  They are also a tent caterpillar.  They come equipped with irritating hairs that can stick in your skin like a tiny harpoon.  They remind me of a Roman Legion Army with its spears sticking out in all directions, staying in line with such determination that they can actually go on a march for days.

"Fabre conducted a famous study on the processionary pine larvae where a group of them were attached nose-to-tail in a circle with food just outside the circle; they continued marching in the circle for a week. The caterpillars may follow a trail of pheromones or silk, but the main stimuli that induce following are from the hairs (setae) on the end of the abdomen of the caterpillar in front. The ant mill is a similar phenomenon."

These however are in one mass, seeming to crawl all over each other in an organized fashion.  Feeling lazy, I sent this off to Kevin Firth and Tom Riley and got my answer back within the day.  Proving again it is not just what you know but who you know.

Larvae- Tom Murray

Kevin sent the Bugguide link to Unidentified Sciarid Larvae and Pupae, the massed larvae of tiny flies called fungus gnats.   The link shows identical pictures of grubs in mass migration.  The individual larvae are not that impressive and very hard to make out in the herd.  The migrations tend to occur in moist weather, frequently in early morning when they can escape the dessication of the sun's rays.

Fungus gnat- by Richard Leung

Bugguide.com describes fungus gnats as "flies are black or brownish, 3mm in length or less and have short antennae.  The veins near the costal margin of the wing (C, R1, and Rs) are heavy, while the remaining veins are quite weak. ... The larvae breed in decaying material and excrement. The group is a small one (61 North American species) but its members are sometimes abundant"  They are said to sometimes eat root hairs of plants and can become a pest in mushroom growing operations.

Tom shared a link to a blog of the Delaware Nature Society demonstrating a continuous circle when the head of the column accidentally merges with the end.  For some reason, this reminds me of my days in the Army.