Bed bug

Bed bugs are parasitic insects of the cimicid family that feed exclusively on blood. The term most commonly refers to members of the genus Cimex of which Cimex lectularius, the common bed bug, is the best known as it prefers to feed on human blood although other Cimex species are specialized to other animals, e.g., bat bugs, C. pipistrelli (Europe), C. pilosellus (western US), and C. adjunctus (entire eastern US).

The name of the "bed bug" is derived from the preferred habitat of Cimex lectularius: warm houses and especially nearby or inside of beds and bedding or other sleep areas. Bed bugs are mainly active at night, but are not exclusively nocturnal. They usually feed on their hosts without being noticed.

A number of adverse health effects may result from bed bug bites, including skin rashes, psychological effects, and allergic symptoms. Diagnosis involves both finding bed bugs and the occurrence of compatible symptoms.

Bed bugs have been known as human parasites for thousands of years. At a point in the early 1940s, they were mostly eradicated in the developed world, but have increased in prevalence since 1995. Because infestation of human habitats has been on the increase, bed bug bites and related conditions have been on the rise as well.

Description

Physical

Adult bed bugs are light brown to reddish-brown, flattened, oval-shaped and have no hind wings. The front wings are vestigial and reduced to pad-like structures. Bed bugs have segmented abdomens with microscopic hairs that give them a banded appearance. Adults grow to 4–5 mm in length and 1.5–3 mm wide.

Newly hatched nymphs are translucent, lighter in colour and become browner as they moult and reach maturity. A bed bug of any age that has just consumed a blood meal will appear to have a bright red translucent abdomen; this colour will fade to brown over the next several hours and within two days will become opaque and black as the insect digests its meal. Bed bugs may be mistaken for other insects, such as booklice, small cockroaches, or carpet beetles, however when warm and active, their movements are more ant-like, and like most other true bugs, they emit a characteristic disagreeable odour when crushed.

Bed bugs use pheromones and kairomones to communicate regarding nesting locations, feeding and reproduction.

The life span of bed bugs varies by species and is also dependent on feeding.

Bed bugs can survive a wide range of temperatures and atmospheric compositions. Below 16.1 °C (61.0 °F), adults enter semihibernation and can survive longer; they can survive for at least five days at −10 °C (14 °F), but will die after 15 minutes of exposure to −32 °C (−26 °F). They show high desiccation tolerance, surviving low humidity and a 35–40 °C range even with loss of one-third of body weight; earlier life stages are more susceptible to drying out than later ones.

The thermal death point for C. lectularius is high: 45 °C (113 °F), and all stages of life are killed by 7 minutes of exposure to 46 °C (115 °F). Bed bugs apparently cannot survive high concentrations of carbon dioxide for very long; exposure to nearly pure nitrogen atmospheres, however, appears to have relatively little effect even after 72 hours.

Feeding habits

Bed bugs are obligatory hematophagous (bloodsucking) insects. Most species feed on humans only when other prey are unavailable. They obtain all the additional moisture they need from water vapor in the surrounding air. Bed bugs are attracted to their hosts primarily by carbon dioxide, secondarily by warmth, and also by certain chemicals.

Their bites are not usually noticed at the time. They develop slowly to low itchy welts that may take weeks to go away. They prefer exposed skin, preferably the face, neck and arms of a sleeping individual. The neck and jaw line are particularly favored places to feed.

Although under certain cool conditions adult bed bugs can live for as long as a year without feeding, under typically warm conditions they will try to feed at five to ten day intervals and adults can survive for about five months without food. Younger instars cannot survive nearly as long, though even the vulnerable newly hatched first instars can survive for weeks without taking a blood meal.

At the 57th Annual Meeting of the Entomological Society of America in 2009, newer generations of pesticide-resistant bed bugs in Virginia were reported to survive only two months without feeding.

DNA from human blood meals from bed bugs can be recovered for up to 90 days, which may allow them to be used for forensic purposes for identifying on whom the bed bugs have been feeding.

Bedbug feeding physiology

A bed bug pierces the skin of its host with what is called a stylet fascicle, rostrum, or "beak". This is a unit composed of the maxillae and mandibles, which have been modified into elongated shapes from a basic, ancestral style. The right and left maxillary stylets are connected at their midline and a section at the centerline forms a large food canal and a smaller salivary canal. The entire maxillary and mandibular bundle penetrates the skin.

The tips of the right and left maxillary stylets are not the same; the right is hook-like and curved, and the left is straight. The right and left mandibular stylets extend along the outer sides of their respective maxillary stylets and do not reach anywhere near the tip of the fused maxillary stylets. The stylets are retained in a groove in the labium, and during feeding, they are freed from the groove as the jointed labium is bent or folded out of the way; its tip never enters the wound.

The mandibular stylet tips have small teeth and through alternately moving these stylets back and forth, the insect cuts a path through tissue for the maxillary bundle to reach an appropriately sized blood vessel. Pressure from the blood vessel itself fills the insect with blood in three to five minutes. The bug then withdraws the stylet bundle from the feeding position and retracts it back into the labial groove, folds the entire unit back under the head, and returns to its hiding place. It takes between five and ten minutes for a bed bug to become completely engorged with blood. In all, the insect may have spent less than 20 minutes in physical contact with its host, and will not attempt to feed again until it has either completed a molt or, if an adult, has thoroughly digested the meal.

Reproduction

All bed bugs mate by traumatic insemination. Female bed bugs possess a reproductive tract that functions during oviposition, but the male does not use this tract for sperm insemination. Instead, the male pierces the female's abdomen with his hypodermic genitalia and ejaculates into the body cavity. In all bed bug species except Primicimex cavernis, sperm are injected into the mesospermalege, a component of the spermalege, a secondary genital structure that reduces the wounding and immunological costs of traumatic insemination. Injected sperm travel via the haemolymph (blood) to sperm storage structures called seminal conceptacles, with fertilisation eventually taking place at the ovaries.

Male bed bugs sometimes attempt to mate with other males and pierce the latter in the abdomen. This behaviour occurs because sexual attraction in bed bugs is based primarily on size, and males will mount any freshly fed partner regardless of sex. The "bed bug alarm pheromone" consists of (E)-2-octenal and (E)-2-hexenal. It is released when a bed bug is disturbed, as during an attack by a predator. A 2009 study demonstrated the alarm pheromone is also released by male bed bugs to repel other males who attempt to mate with them.

C. lectularius and C. hemipterus will mate with each other given the opportunity, but the eggs then produced are usually sterile. In a 1988 study, one of 479 eggs was fertile and resulted in a hybrid, C. hemipterus × lectularius.

Life stages

Bed bugs have six life stages (five immature nymph stages and a final sexually mature adult stage). They will shed their skins through ecdysis at each stage, discarding their outer shells which are clear, empty exoskeletons of the bugs themselves. Bed bugs must molt six times before becoming fertile adults and must take a blood meal in order to complete each molt.

Each of the immature stages lasts approximately a week, depending on temperature and the availability of food, and the complete life cycle can be completed in as little as two months (which is actually rather long compared to other ectoparasites— fleas, for example, can complete a cycle in as little as three weeks). Fertilized females with enough food will lay three to four eggs each day continually until the end of their life spans (about nine months under warm conditions), possibly generating as many as 500 eggs in this time.

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  Slide of Cimex lectularius

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  Bed bug (4 mm length; 2.5 mm width), shown in a film roll plastic container, on the right is the recently sloughed skin from its nymph stage

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  A bed bug nymph feeding on a host

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  Blood-fed Cimex lectularius (Note the differences in colour with respect to digestion of blood meal)

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  A bed bug with hunger bubbles visible in its gut

Infestation

Bed bugs can cause a number of health effects, including skin rashes, psychological effects, and allergic symptoms. They are able to be infected by at least 28 human pathogens, but no study has clearly found the insect is able to transmit the pathogen to a human being. Bed bug bites or cimicosis may lead to a range of skin manifestations from no visible effects to prominent blisters.

Diagnosis involves both finding bed bugs and the occurrence of compatible symptoms. Treatment involves the elimination of the insect and measure to help with the symptoms until they resolve. They have been found with methicillin-resistant Staphylococcus aureus MRSA and with vancomycin-resistant Enterococcus faecium ( VRE), but the significance of this is still unknown.

Cause

Dwellings can become infested with bed bugs in a variety of ways, such as:

• Bugs and eggs inadvertently brought in from other infested dwellings by visiting pets; or a visiting person's clothing or luggage;
• Infested items (such as furniture, clothing, or backpacks) brought in;
• Nearby dwellings or infested items, if easy routes are available for travel (through duct work or false ceilings);
• Wild animals (such as bats or birds) that may also harbour bed bugs or related species such as the bat bug;
• People or pets visiting an infested area (apartment, subway, movie theatre, or hotel) and carrying the bugs to another area on their clothing, luggage, or bodies.

Detection

Bed bugs are elusive and usually nocturnal (peak activity usually occurs around 5:00 or 6:00 a.m.), which can make noticing them difficult. They often lodge in dark crevices, and the tiny adhesive eggs can be nestled by the hundreds in fabric seams. Aside from bite symptoms, signs include fecal spots (small dark sand-like droppings that occur in patches around and especially beneath nests), blood smears on sheets (fecal spots that are re-wetted will smear like fresh blood), and the presence of their empty molted exoskeletons.

Although bed bugs can be found singly, they tend to congregate once established. Although they are strictly parasitic, they spend only a tiny fraction of their life cycles physically attached to their hosts. Once feeding is complete, a bed bug will relocate to a place close to a known host, commonly in or near beds or couches in clusters of adults, juveniles, and eggs which entomologists call harborage areas or simply harborages to which the insect will return after future feedings by following chemical trails. These places can vary greatly in format, including luggage, inside of vehicles, within furniture, amongst bedside clutter, even inside electrical sockets and nearby laptop computers. Bed bugs may also nest near animals that have nested within a dwelling, such as bats, birds, or rodents.

Bed bugs can be detected by their characteristic smell of rotting raspberries. Bed bug detection dogs are trained to pinpoint infestations, with a possible accuracy rate of 97.5%, based upon tests conducted under controlled conditions by researchers. The success rates in these tests may not reflect real-world success rates of pest companies’ dogs, operating with many more variables in the field.

Dog detection can often occur in minutes where a pest control practitioner might need an hour. In the United States, about 100 dogs are used to find bed bugs as of mid-2009. A few companies are experimenting with high speed gas chromatography to detect bed bugs.

Management

Eradication of bed bugs frequently requires a combination of pesticide and nonpesticide approaches. Pesticides that have historically been found to be effective include: pyrethroids, dichlorvos and malathion. Resistance to pesticides has increased significantly over time and negative health effects from their use are of concern.

Mechanical approaches, such as vacuuming up the insects and heat treating or wrapping mattresses, have been recommended. A combination of heat and drying treatments have been found to be most effective. For public health reasons, individuals are encouraged to call a professional pest control service to eradicate bed bugs in a home, rather than attempting to do it, themselves, particularly if they live in a multi-family building.

The carbamate insecticide propoxur is highly toxic to bed bugs, but in the United States the Environmental Protection Agency (EPA) has been reluctant to approve such an indoor use because of its potential toxicity to children after chronic exposure.

Although occasionally applied as a safe indoor pesticide treatment for other insects, boric acid is ineffectual against bed bugs because bed bugs do not groom. The fungus Beauveria bassiana is being researched for its ability to control bed bugs.

Predators

Natural enemies of bed bugs include the masked hunter insect (also known as "masked bed bug hunter"), cockroaches, ants, spiders (particularly Thanatus flavidus), mites and centipedes. The Pharaoh ant's (Monomorium pharaonis) venom is lethal to bed bugs. Biological pest control is not very practical for eliminating bed bugs from human dwellings.

Epidemiology

Bed bugs occur around the world. Rates of infestations in developed countries, while decreasing from the 1930s to the 1980s, have increased dramatically since the 1980s. Previously, they were common in the developing world, but rare in the developed world. The increase in the developed world may have been caused by increased international travel, resistance to insecticides, and the use of new pest-control methods that do not affect bed bugs.

The fall in bed bug populations after the 1930s in the developed world 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. Others believe it might simply be the cyclical nature of the organism.

The exact causes of this resurgence remain unclear; it is variously ascribed to greater foreign travel, 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 resistance to pesticides.

The common bed bug (Cimex lectularius) is the species best adapted to human environments. It is found in temperate climates throughout the world. Other species include Cimex hemipterus, found in tropical regions, which also infests poultry and bats, and Leptocimex boueti, found in the tropics of West Africa and South America, which infests bats and humans. Cimex pilosellus and Cimex pipistrella primarily infest bats, while Haematosiphon inodora, a species of North America, primarily infests poultry.

History

C. lectularius may have originated in the Middle East in caves inhabited by bats and humans.

Bed bugs were mentioned in ancient Greece as early as 400 BC, and were later mentioned by Aristotle. Pliny's Natural History, first published circa 77 AD in Rome, claimed bed bugs had medicinal value in treating ailments such as snake bites and ear infections. (Belief in the medicinal use of bed bugs persisted until at least the 18th century, when Guettard recommended their use in the treatment of hysteria.)

Bed bugs were first mentioned in Germany in the 11th century, in France in the 13th century and in England in 1583, though they remained rare in England until 1670. Some in the 18th century believed bed bugs had been brought to London with supplies of wood to rebuild the city after the Great Fire of London (1666). Giovanni Antonio Scopoli noted their presence in Carniola (roughly equivalent to present-day Slovenia) in the 18th century.

Traditional methods of repelling and/or killing bed bugs include the use of plants, fungi, and insects (or their extracts), such as black pepper; black cohosh (Actaea racemosa); Pseudarthria hookeri; Laggera alata (Chinese yángmáo cǎo | 羊毛草); Eucalyptus saligna oil; henna (Lawsonia inermis or camphire); "infused oil of Melolontha vulgaris" (presumably cockchafer); fly agaric (Amanita muscaria); Actaea spp. (e.g. black cohosh); tobacco; "heated oil of Terebinthina" (i.e. true turpentine); wild mint (Mentha arvensis); narrow-leaved pepperwort (Lepidium ruderale); Myrica spp. (e.g. bayberry); Robert geranium (Geranium robertianum); bugbane (Cimicifuga spp.); "herb and seeds of Cannabis"; "opulus" berries (possibly maple or European cranberrybush); masked hunter bugs (Reduvius personatus), "and many others".

In the mid-19th century, smoke from peat fires was recommended as an indoor domestic fumigant against bed bugs.

Dusts have been used to ward off insects from grain storage for centuries, including "plant ash, lime, dolomite, certain types of soil, and diatomaceous earth or Kieselguhr". Of these, diatomaceous earth in particular has seen a revival as a nontoxic (when in amorphous form) residual pesticide for bed bug abatement. Insects exposed to diatomaceous earth may take several days to die.

Basket-work panels were put around beds and shaken out in the morning in the UK and in France in the 19th century. Scattering leaves of plants with microscopic hooked hairs around a bed at night, then sweeping them up in the morning and burning them, was a technique reportedly used in southern Rhodesia and in the Balkans.

20th century

Prior to the mid-20th century, bed bugs were very common. According to a report by the UK Ministry of Health, in 1933, all the houses in many areas had some degree of bed bug infestation. The increase in bed bug populations in the early 20th century has been blamed on the advent of electric heating, which allowed bed bugs to thrive year-round instead of only in warm weather.

Bed bugs were a serious problem at U.S. military bases during World War II. Initially, the problem was solved by fumigation, using Zyklon Discoids that released hydrogen cyanide gas, a rather dangerous procedure. Later, DDT was used to good effect as a safe alternative.

The decline of bed bug populations in the 20th century is often credited to potent pesticides that had not previously been widely available. Other contributing factors that are less frequently mentioned in news reports are increased public awareness and slum clearance programs that combined pesticide use with steam disinfection, relocation of slum dwellers to new housing, and in some cases also follow-up inspections for several months after relocated tenants moved into their new housing.

Resurgence

Bed bug infestations have resurged in recent years for reasons which are not clear, but contributing factors may be complacency, increased resistance, bans on pesticides and increased international travel. 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.

One recent theory about bed bug reappearance is that they never truly disappeared from the United States, but may have been forced to alternative hosts. Consistent with this is the finding the bed bug DNA shows no evidence of an evolutionary bottleneck. Furthermore, investigators have found high populations of bed bugs at poultry facilities in Arkansas. Poultry workers at these facilities may be spreading bed bugs, unknowingly carrying them to their places of residence and elsewhere after leaving work.

Society and culture

The saying, "Good night, sleep tight, don't let the bed bugs bite", is common for parents to say to young children before they go to sleep.

Etymology

The word bug and its earlier spelling bugge means bedbug. Many other creatures are called bugs, such as the lady bug (ladybird outside the U.S), the potato bug, or the slang use of the word for any insect, or even for microscopic germs, or diseases caused by these germs, but the earliest recorded use of the actual word bug, was to mean bedbug.

The term bed bug may also be spelled bedbug or bed-bug, though published sources consistently use the unhyphenated two-word name bed bug. They have been known by a variety of other names, including wall louse, mahogany flat, crimson rambler, heavy dragoon, chinche bug, and redcoat.