Robert Irwin Poses in Only Underwear, With Snakes and Spider on His Torso

Robert Irwin's getting almost as naked as the animals he hangs out with ... stripping to his "down undies" for an exclusive photo shoot with People.

The Australian conservationist left little to the imagination in a new ad for Bonds -- an Aussie underwear brand launching in the United States.

Robert's showing off his ripped abs and strong legs in the photos ... lying out on the grass and posing up against a fence in the photos.

As per usual ... Robert's hanging out with some animal pals in the pics -- including a spider and a couple of massive snakes. He's got the snakes wrapped around his neck and the spider just chilling on his shoulder, clearly at ease around animals just like his dad, Steve.

Worth noting ... People writes the spiders with Robert in the campaign were mostly venomous -- which he tells the outlet doesn't bug him one bit 'cause he's been courting danger around animals for years.

As for what he finds more intimidating -- stripping down to his skivvies or wrangling a crocodile -- Robert's clear ... he'd take the croc any day of the week.

As you know ... Steve passed away back in 2006 after swimming over the top of a stingray which stabbed the poisonous barb at the end of its tail into his heart. He was 44.