"They are so smart, and they tend to sneak up and attack from behind, often grabbing at your legs," city official Masato Saito tells the AP. "I have never seen anything like this my entire life." Japanese macaques (Macaca fuscata), also called snow monkeys, are well-known for their habit of bathing in hot springs during the winter. They typically live in troops of about 20 to 30, but the groups can sometimes have more than 100 individuals. These monkeys were once considered endangered in Japan, but their population has rebounded, and they are now listed as least concern by the International Union for Conservation of Nature. The animals can live about 22 to 27 years. Male Japanese macaques weigh about 25 pounds while females are about 18.5 pounds.