Giant mesquite bugs — the juveniles are red and white — seek cooler temperatures near or on the ground.

How hot is it in Tucson? So hot that giant mesquite bugs are coming down from their normal domain in the tops of mesquite trees in search of heat relief near the ground.

The imposing insects — up to 2 inches in length — are harmless to humans, but they’re nevertheless startling to some people because of their size.

“They are these beautiful gentle giants that typically hang out in the canopy of mesquite trees,” said University of Arizona entomologist Gene Hall. “But whenever temperatures get brutally hot, they go down to the base of the tree to try to cool off.”

“We’re seeing them frequently in the last few weeks,” said Hall, who manages the university’s insect collection in addition to other duties with the College of Agriculture and Life Sciences. “I’m getting photos almost every day from people who see them.”

Coming across a cluster of mesquite bugs is largely a matter of chance. The most likely time to find them on lower mesquite trunks is at the hottest part of the day.

“We sometimes find them in large numbers at the base of a tree,” Hall said. “It’s their way of escaping the high heat up in the canopy. It’s cooler and shadier near the ground. They need to get out of the sun and heat.”

One place Hall has seen mesquite bugs near the ground is on mesquite trees near the Forbes Building on the UA campus. The building is immediately south of Old Main.

LIFE CYCLE

Mesquite bugs live and feed on mesquite trees at this time of year and lay eggs on the trees by late summer. The eggs hatch in the spring.

“They are up in the trees, feeding off the plant, but they don’t harm the plant,” Hall said. “They feed on tender parts of the plant. They are completely harmless and don’t attack people.”

He said juvenile mesquite bugs are red with white markings on the abdomen.

“In the adult stage, they have wings in a blackish-grayish color with yellowish markings on them,” Hall said.

Contact reporter Doug Kreutz at dkreutz@tucson.com or at 573-4192. On Twitter: @DouglasKreutz