8/4/98

I just witnessed something I have never seen in my entire life.  Driving home from work, the hot Tucson summer sun was setting and across the entire road for hundreds of yards, I could see little movements and long shadows everywhere.  I quickly pulled over, and noticed that the movements were 3 to 4 1/2" yellow caterpillars, apparently running across the hot pavement. Hundreds, probably thousands of them.  Their carcasses lay splattered everywhere (this is a heavily-traveled road in the northwest of Tucson) across from the Overton Fine Arts Center.

I caught one and tried to identify it with my Golden Guide to Butterflies and Moths, but no luck.  Closest match appeared to be the White-lined sphinx, but mine was very yellow, with 2 black lines along the back, white lines beneath the black ones, and some red and white markings around the lines. An orange-ish pointed tail was almost always visible and seemed to be used in self defense.  I saw a few less mature larvae, which were all green with 2 white stripes (that must later become black?) and some red and black markings.

What kind of caterpillars do you think these are?
Why was there such a mass exodous across the busy, hot road?

I emailed a few addresses at the University of Arizona, and this is what I got back:

• Hyles lineata (white-lined sphinx) often builds up to big populations at about this time of year, and what you saw is a relatively common event. They do become very mobile in the later stages of development. -Reg Chapman, 8/1998
• Probably the sphinx moth... which is also known as maduca sexta. -Dane Wachs, 8/1998
• White-lined Sphinx moth caterpillars, Hyles lineata. Occurs every year with varying populations and localities. Normally move to either find good place to burrow into soil and pupate or to locate new food source. -Carl Olson, 8/1998

• It's a White Lined Sphinx Larva. Just visit desertusa.com.
  - Alea Ishikawa, 6/2002