He was an outspoken critic of Rachel Carson and efforts to ban DDT, famously eating the substance to demonstrate its safety to humans. He was also a noted mountain climber, spending nine seasons as a ranger-naturalist in Glacier National Park during the 1940s and '50s, and returning often to collect insects and map routes. His 1961 book A Climber's Guide to Glacier National Park, republished several times since, made him known as the "patron saint of climbing" in the park, where he died while hiking, aged 84.