The changes in humidity and barometric pressure brought by the monsoon trigger the adult beetles to come above ground. They spend three years eating the roots of palo verde trees before emerging.
Their spiny legs, long antennae and large jaws may be intimidating, but experts say the beetles pose no threat, unless they're bothered.
"They're not coming after us," said Daniel Marchand of the Phoenix Herpetological Society, "They're just looking to do their thing, mate, and lay eggs before they die."
Palo verde beetles are one of the largest beetles in North America, often growing up to be several inches long. Adept on the ground, these beetles, which some say resemble large cockroaches, also can fly.
Most active in the early evening hours, the beetles' above-ground life lasts only about two months, so they should disappear by the end of August.