In 2014, bright-green caterpillars were swarming Phoenix. One longtime resident witnessed the wrigglers crossing Happy Valley Road and wanted to know what brought them there.

Tim Agne/KJZZ

White-lined sphinx caterpillar in Arizona.

Hyles lineata, better known as the White-lined Sphinx for its brightly veined wing pattern, sports a 2 1/2 to 3 1/2 inch wingspan and enjoys a wide variety of open habitats, from deserts to suburban gardens.

Its larvae chow down on a broad menu of plants, from flowers to weeds to tomatoes.

Under the right conditions — as Phoenix had in 2014 — they can achieve truly massive populations.

"When there are very favorable spring conditions in terms of rainfall and plant growth is most likely when these kinds of population explosions tend to occur," said Nico Franz, director of Arizona State University's Biocollections and curator of its insect collection.

So keep a close eye on that salsa garden — and watch your step. 

ASU Biocollections.

Hyles lineata, also known as the white-lined sphinx.