Friday, October 8, 2010

Why do Caterpillars Cross the Road?

There's an old saying - caterpillars crossing the road is a sign that fall is here.  Despite record-setting temperatures (81-degrees), I'm seeing caterpillars on the road everywhere.

Caterpillars crossing the road.  Who are they?  Where are they going?

Most of them are Isabella Tiger Moth caterpillars, aka Woolly Bear caterpillars.  There were so many today, I stopped counting - approximately 1 every 100 yards along County Road M in Durand.  They overwinter as caterpillars, so it may be that they're heading to a better place for hibernating.  We stopped and watched a half dozen - just to see how they handled the road crossing.

When cars zoomed by (and didn't squish them) the woolly bears stopped and curled up (would that this defense could protect them from vehicles).   Tiny caterpillars v. SUVs and pickups.

Some caterpillars headed east.  Some went west.  And one couldn't seem to make up its mind, heading back and forth, then up and down the road.

One seemed larger and all black.  I stopped again for a closer look.  I didn't have a clue what it was until I picked it up and it went into its defense curl... the red skin was the give away - a Giant Leopard Moth caterpillar.   It's about 2" long (half an inch longer than the woolly bear).

Further down the road I stopped for what looked like an orange woolly bear...

Turns out this one's called a Yellow Bear, or Virginian Tiger Moth caterpillar.  Its color varies from blonde to very dark, almost black.

A hundred yards down the road - there's another one... much smaller and scurrying much faster.  I'd have thought this one would be easy to identify... but I'm stumped.  So I went to and uplinked it.  Turns out it's a Phyllira Tiger Moth a species of special concern in Wisconsin.

Back to the original question:  why do these caterpillars cross the road?

My husband is convinced it has something to do with the "heat."  I think it has nothing to do with the road - they're just looking for that perfect place to hibernate and the road is in their way.

1 comment:

  1. This morning, Sept 10th, 2013, while on my motorcycle in the Southern California desert in San Diego County I came upon a very dense and very long mass of larger yellow caterpillars migrating across the road. When I say dense, I mean there were roughly six to eight in a square meter, and when I say long I mean that I rode well over half a mile if not much more of these determined little beggars. It was indeed quite a sight. The weather has been 100F plus during the day in this area and the rains have been very heavy lately so I imagine the combo got them riled up and they're out looking for more accommodating domiciles. Wow!!