Homestead Air Reserve Base near Miami, Florida, is dealing with a different sort of small ground invasion: the Nile monitor lizard. These invasive reptiles—possibly former family pets or escapees from nearby breeding facilities—occasionally lumber onto the base's tarmac to soak up the sun's rays. "When you have an airplane coming in to land or take off, and you have a 6-foot [1.8-meter] reptile laying on the runway, it causes a substantial human health and safety problem," said Parker Hall, a wildlife biologist with the U.S. Department of Agriculture's Wildlife Services. Agency employees patrol the runways on a regular basis to...