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The two species of bed bugs (Hemiptera: Cimicidae) usually implicated in human infestations are Cimex lectularius and C. hemipterus. Humans may also rarely become incidental hosts of Cimex species that normally fed on bats and birds. Although C. lectularius has a cosmopolitan distribution, C. hemipterus is limited to the tropics and sub-tropics.
The bed bug Cimex lectularius is a member of the family Cimicidae, a group of true bugs that are highly specialized for feeding on blood, mainly that of humans, birds, and bats. All these hosts occur in temporally and spatially predictable, gregarious assemblages in or around enclosed spaces such as caves or buildings and all have a relatively high body temperature. Cimex lectularius has been closely associated with humans for thousands of years (it is one of several cimicid species for which humans are the primary host). Despite this close association, however, it survives well on bird, bat, and rabbit hosts in the laboratory (in fact, it produces more eggs, and the hatched nymphs develop faster, when reared on mice, a host rarely encountered in nature) and has been found in the wild on several different bird and bat hosts. Nymphs of C. lectularius die within a few days of hatching if they do not feed and egg production ceases soon after adult females are prevented from feeding. Cimicids all mate by traumatic insemination, during which the male pierces the female’s abdominal wall (see Reproduction). (Reinhardt and Siva-Jothy 2007 and references therein)
There appears to have been a dramatic increase of C. lectularius in the developed world--notably in North America, Europe, and Australia--beginning in the 1980s or 1990s, particularly in hotels. Reinhardt and Siva-Jothy (2007) suggest that although these increases are facilitated by cheap air transport and increased travel, they are probably exacerbated by the disappearance of folk knowledge of these insects in the developed world. For example, most people under age 50 in the developed world have no ability to recognize (e.g., by smell) bed bugs and to take early measures to control infestations of these insects. (Reinhardt and Siva-Jothy 2007 and references therein) Another important factor in the recent resurgence in bedbug infestations in human dwellings seems to be the widespread evolution of resistance to commonly used pesticides (Romero et al. 2007).
Adults and all nymphal stages of Cimex species need to take blood meals from warm-blooded hosts, which are typically humans for C. lectularius and C. hemipterus, although other mammals and birds can be utilized in the absence of a human host. Female bed bugs lay about five eggs daily throughout their adult lives in a sheltered location (mattress seams, crevices in box springs, spaces under baseboards, etc). Eggs hatch in about 4-12 days into first instar nymphs which must take a blood meal before molting to the next stage. The bugs will undergo five nymphal stages, each one requiring a blood meal before molting to the next stage, with the fifth stage molting into an adult. Nymphs, although lacking wing buds, resemble smaller versions of the adults. Nymphs and adults take about 5-10 minutes to obtain a full blood meal. The adults may take several blood meals over several weeks, assuming a warm-blooded host is available. Mating occurs off the host and involves a unique form of copulation called ‘traumatic insemination’ whereby the male penetrates the female’s abdominal wall with his external genitalia and inseminates into her body cavity. Adults live 6-12 months and may survive for long periods of time without feeding. (Centers for Disease Control Parasites and Health website)