Agency has been reluctant to approve it for indoor use. Boric acid, occasionally applied as a safe indoor insecticide, is not effective against bed bugs because they do not groom. Epidemiology Bed bugs occur around the world. Before the 1950s about 30% of houses in the United States had bedbugs. This percentage has since fallen, which is believed to be partly due to the use of DDT to kill cockroaches. The invention of the vacuum cleaner and simplification of furniture design may have also played a role in the decrease. Others believe it might simply be the cyclical nature of the organism. However, rates of infestation in developed countries have increased dramatically since the 1980s. This is thought to be due to greater foreign travel, increased immigration from the developing world to the developed world, more frequent exchange of second-hand furnishings among homes, a greater focus on control of other pests, resulting in neglect of bed bug countermeasures, and increasing bedbug resistance to pesticides. Lower cockroach populations due to insecticide use may have aided bed bugs' resurgence, since cockroaches are known to sometimes prey on them. Steadily-rising resistance to DDT and other potent pesticides may have also contributed; bans on DDT may have contributed as well, though studies have shown resistance continued to rise in countries where they continued to be used. The U.S. National Pest Management Association reported a 71% increase in bed bug calls between 2000 and 2005. The number of reported incidents in New York City alone rose from 500 in 2004 to 10,000 in 2009. In 2013, Chicago was listed as the number one city in the United States for bedbug infestations. As a result, the Chicago City Council passed a bed bug control ordinance to limit their spread. Additionally, bed bugs are reaching places in which they never established before, such as southern South America. The rise in infestations has been hard to track because bed bugs are not an easily identifiable problem and is one that people prefer not to discuss. Most of the reports are collected from pest-control companies, local authorities, and hotel chains. Therefore, the problem may be more severe than is currently believed. Species The common bed bug (Cimex lectularius) is the species best adapted to human environments but is also known from birds, Chiroptera, Gallus (chickens and relatives), Myotis myotis, and sheep (Ovis aries). It is found in temperate climates