A Western diamondback rattlesnake lives at the Arizona-Sonora Desert Museum.

Sure signs of spring in the desert: warming weather, blooming cacti — and rattlesnakes slithering out of their dens.

The venomous vipers are out and about around Southern Arizona, and they’re biting.

“We’ve had 24 bites reported so far this year — 12 bites in March and another 12 in April,” said Keith Boesen, director of the Arizona Poison and Drug Information Center.

And the biting season is just getting underway.

“The number of reported bites usually hovers in the double digits through May, June and July and then jumps to about 30 in August and September,” Boesen said. “It’s about a bite a day during those months before tapering off in October and November.”

MANY SIGHTINGS

Rattlesnakes typically come out of their winter dens in March or April, but uncommonly warm winter and spring weather brought some out earlier this year, said Randy Babb, a biologist with the Arizona Game and Fish Department.

“We had those real warm snaps early on, so they’ve been out for a while,” Babb said, noting that snake sightings have been common.

“We saw eight or so of them when we were out on a research project recently,” he said.

WIDE-RANGING RATTLERS

Babb said Arizona is home to 13 species of rattlesnakes, with eight or nine species living in Southeastern Arizona, depending on how the region is defined.

They range far and wide — from deserts, canyons and forests to urban backyards.

Some rattlers slither a mile or more from their dens to places where they spend the summer, Babb said.

A BIT ABOUT BITES

Boesen said 150 to 160 rattlesnake bites are reported every year to the Poison and Drug Information Center, which covers all Arizona counties except Maricopa County. Another center keeps track of bites there.

Rattlesnakes — sometimes called “buzzworms” because of the buzzing sound of their rattles — sometimes rattle before striking, but not always.

Some rattlesnake bites are so-called “dry bites” in which no venom is injected.

“During the last two seasons, the dry-bite rate was 19 percent in our patients,” Boesen said.

He said the best response to a bite is to go immediately to a medical facility for examination and treatment with anti-venom if needed.

“No cutting, no sucking, no tourniquets — none of that,” Boesen advised. “Just get to a hospital.”

He said plenty of anti-venom is available in Arizona this year.

Boesen and Babb said deaths from rattlesnake bites are extremely rare, and that there have been no known recent snakebite deaths in Southern Arizona.

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