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Why The Phoenix Area Is Crawling With Bright Green Caterpillars

Published: Friday, August 27, 2021 - 11:16am
Updated: Sunday, August 29, 2021 - 8:42am
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Many Maricopa County residents are noticing a curious side effect of the monsoons: a sizable increase in the numbers of caterpillars wandering their neighborhoods.

They are about a half inch to an inch in length and can be green, yellow and red — and people are seeing them migrating in huge masses.

Gene Hall is collection manager for the University of Arizona’s Insect Collection, and he noted that these numbers could pose some risks for drivers, specifically.

“Sometimes it gets to the point where roads are just covered with these things. And it could be slippery conditions. It could get that bad at times," Hall said.

Hall explained that this is a result of the incredible amount of rain we’ve received during this monsoon season — more rain means more plants, and more plants means more food for insects and larvae.

Q&AZ: Where Did All The Green Caterpillars Come From?

But after stuffing themselves, these caterpillars won't morph into butterflies.

“This particular caterpillar, once it's gotten enough to eat, will wander around, will look for some place to dig into the ground, and then it will pupate and then it will emerge as a white-lined sphinx moth," Hall said.

Hall said these caterpillars shouldn’t do too much damage to gardens and landscaping, and they will have no impact on any of the region’s farming operations.

But what kind of impact will this caterpillar-pocalypse have on the desert’s fauna?

“These caterpillars — they definitely provide a food source for other animals, and I’ve heard that even hawks like to eat these caterpillars. And also, here in the Southwest, Native Americans used to eat these caterpillars, too, if I remember correctly, as a food source.”

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