That includes bed bugs (Cimex lectularius). The theory goes that about 60,000 years ago, a few intrepid bed bugs hopped off of a bat and clung to a Neanderthal walking out of a cave. However, the less adventurous bat-living bed bugs have seen their populations decline since the Last Glacial Maximum–aka ice age–about 20,000 years ago. Understanding the historical and evolutionary relationship between humans and bed bugs can help inform models that predict the spread of bugs and diseases as urban populations increase. “Bed bugs were pretty common in the old world, but once DDT [dichloro-diphenyl-trichloroethane] was introduced for pest control, populations crashed.