Damon, wife Luciana Barroso and daughters Isabella, 13, Gia, 11, and Stella, 9, spent time with Hemsworth, the actor's wife, Elsa Pataky, and their children, daughter India, 7, and twin sons Sasha and Tristan, 5, in western Australia.
Host Ellen DeGeneres said Hemsworth, a native of Australia, told her that Damon is bad luck.
"I stepped on a snake the last time I was there," Damon said. "Like, an eight-foot python. I was getting out of a car -- that's how many things in Australia are like, crazy."
"We were going to the beach and were going to hike down this little trail. I got out of the car and stepped on something that felt like a giant piece of wood. I looked down and it was a snake," he added. "It didn't even really notice that I was on it."
Damon also said his daughter Stella got stung by a jellyfish. He denied that you are supposed to pee on someone if they get stung.
"What you're supposed to do is put somebody in a really hot bath and get a sponge and gently move the little -- because there's these tiny little needles in you when one of them stings you -- brush them out," the star said.
Damon, Hemsworth and their families visited Australia in March. Pataky previously told People she and Hemsworth met Damon and his family through mutual friends.
"They are such amazing people," Pataky said. "We have three kids, they have four kids, so we ended up making the same plans because everything we do we do with the kids, so it's easier to do things with people that understand you."