Bed bugs feed on blood. They used to be a major nuisance in Norway but the introduction of insecticides almost eradicated them in the 1950s. However, due to insecticide resistance and increased global travel, their incidence has risen sharply in many parts of the world over the last 15 years.
The common bed bug (Cimex lectularius) lives indoors and in recent years has become much more common in Norway. In the tropics, the bed bug species C. hemipterus and Leptocimex boueti also feed on humans. The latter is only found in Africa. In Norway, bat bugs (C. dissimilis) and swallow bugs (Oeciacus hirundinis) may occasionally come indoors and bite humans.
Bed bugs are reddish-brown with an oval, flat body shape (Figure 1). Adults are 5-6 mm long and 3 mm wide. The nymphs resemble adults but they are smaller and lighter in colour. The eggs are 1 mm long and white (figure 2). When bed bugs suck blood, they swell and darken (figure 3). They have no wings and their mouth parts form a long, articulated suction tube (proboscis) which is pointed backwards under the head and thorax. The proboscis points forward when in use. Bed bugs emit a characteristic odour.
Bed bug reproduction and development is highly dependent on temperature and food availability. Females normally lay 1-2 eggs per day and may produce 200-500 eggs during adulthood. Eggs are glued to their hiding places (Figure 2). It takes 4-21 days before a nymph hatches from an egg. Nymphs have five development stages and they must feed at least once between each stage. At optimal temperatures (28-30 ̊C) and humidity (75-80% RH) the entire life cycle takes four to five weeks. At low temperatures, the development time can take up to a year.
Activity stops when the temperature drops below 10 ̊C. Bed bugs can survive without food for long periods. At 10 ̊C, adults can survive without blood for over a year, while the smallest nymphs can survive for up to nine months. Although bed bugs like to feed on human blood, they can also suck blood from other mammals such as bats, cats and dogs as well as birds.
Bed bugs feed on blood
Bed bugs usually active at night and suck blood from bites in exposed skin. An adult bed bug will feed for 5-10 minutes before scurrying back to its hiding place where digestion, skin-shedding and egg-laying occurs. Their characteristic brown-black excrement can usually be found here too (Figure 4). With regular access to food, bed bugs will feed weekly at room temperature.
There are large individual differences in how humans react to bed bug bites. Some experience severe, itchy weals, while others experience a milder (Figure 5) or no reaction. The reaction to a bite can appear immediately or after some time. With repeated bite episodes, reactions will appear more quickly and become stronger.
Do bed bugs transmit infectious diseases?
Bed bugs do not normally transmit diseases to humans. A number of pathogenic microorganisms have been found in bed bugs that have fed from infected people, but only Trypanosoma cruzi, which causes Chagas disease has been shown to survive for long in bed bugs. There is a slight risk of infection from bed bug excrement in human skin wounds.
The bites can be very irritating and scratching them may cause secondary infections.
Bed bugs can travel with luggage, used furniture, other household contents and used bed linen. They are usually found in places with a high turnover of guests, such as hotels, cabins, youth hostels and student accommodation. Bed bugs may then be transported to new accommodation or private homes. Once bed bugs have established themselves in a room, they can spread to other rooms or apartments in the same building.
Bed bugs are usually found where people sleep (bed or sofa) and they hide in crevices and small holes (Figure 2 and 4). Bed bugs may also be found quite far away from the bed. They may hide behind cupboards and pictures, in cracks in panels, behind skirting boards, coving, door and window frames, behind loose wallpaper, in sockets and electrical appliances, behind wiring or in pipe conduits.
Empty skins, eggs and excrement are often found where they hide, as well as living and dead bed bugs. The black excrement is often easiest to spot (Figure 4). If bed bugs are discovered in one room, check the adjacent room and elsewhere in the house to see if more treatment is needed.
Bed bugs are often brought into the residence in luggage that has been in accommodation infested with bed bugs.
Take these precautions when traveling:
- Check the underside of the bed at your accommodation for excrement and bed bugs. Also look in cracks and lift the fabric edges in the bed where possible. Ensure good lighting, for example with a torch or the flashlight app on a mobile phone. If you see bed bugs or if you suspect there are traces of them do not stay in the room. Contact the reception immediately and ask them to examine the room carefully. Request a new room or move to different accommodation if you are in doubt.
- Store your belongings in the suitcase at all times and only take out what you need.
- Place the suitcase away from the bed, preferably on a suitcase stand if available.
- If you have stayed in a place where bed bugs are suspected, luggage should be cold or heat treated before taking it into your home.
Second-hand furniture (beds, mattresses, sofas, chairs, etc.) may contain bed bugs. Examine these objects thoroughly before taking them home. Freezing or heat treating the object can also be considered.
It is unlikely that bed bugs will be found in clothing or other items after day visits to affected locations. However, if there are many insects present, there is a certain risk that bed bugs can crawl into bags and shoes. Take minimal belongings into the residence and place them away from beds and furniture.
Effective bed bug control is difficult and professional help is advised. Several different control methods should be combined to increase the probability of a successful outcome. When bed bugs are discovered in hotels, student accommodation, apartment blocks and other large properties, control methods should be co-ordinated for a successful result.
Bed bugs can survive for long periods without food, they have many hiding places and they can move between rooms and apartments. Sealing cracks and other small openings will reduce the number of hiding places and increase the probability of successful control.
Vacuuming can be used to remove as many insects as possible but this alone does not provide adequate control. Dispose of the vacuum cleaner bag carefully after use to prevent bed bugs from escaping.
Limit the use of chemical insecticides. Beds, clothes and other loose objects should be either cold or heat treated. Wrap infested objects that will be transported for cold or heat treatment or to the rubbish dump for disposal so that the bed bugs cannot spread during transit. An effective cold treatment that kills eggs, nymphs and adult bed bugs is done by freezing the items at -18°C for three days. The freezing period must be long enough for the objects to be at the correct temperature for three days. A freezer room or freezer can be used. Heat treatment can take place in a sauna, drying cabinet, tumble dryer or special tent designed for bed bug treatment. The temperature must be above 50°C for a few hours. Again, objects need to be treated for long enough at the correct temperature. Using a washing machine at a minimum temperature of 60ºC is also an option.
When all loose items that can be cold or heat-treated are treated, skirting boards, covings, small gaps and cracks in walls can also be heat or cold-treated. There is little evidence about the efficacy of the treatment but if the insects are exposed to a high or low enough temperature, they will die quickly. Thorough efforts are needed to be able to kill all the bed bugs that are well hidden in small gaps. Special equipment has been developed that produces steam with suitable pressure and temperature. The materials that are exposed to steam must tolerate 100 °C and some moisture. As with steam, point treatment with dry ice (CO2 at -80 °C) can be directed and can be used on electric appliances.
Heat treatment of rooms or entire buildings is a commonly used method. Eradication is labour and energy intensive, but if a high enough temperature is achieved so that all the bed bugs and eggs are exposed for a sufficient period of time, they can be removed.
Silica powder and diatomaceous earth can also be used to control bed bugs. These powders kill because they damage the insects' skin (cuticle) and dry them out.
Bed bugs have evolved resistance to insecticides which makes chemical treatment difficult, and sprays should be used only in combination with other methods. For health reasons their use should be limited. When chemical agents are used, it is important to spray directly on their hiding places. Beds should not be treated with insecticides. All possible hiding places such as wall decorations, pictures, coat hooks, skirting boards and covings, loose wallpaper or loose floor coverings should be removed prior to spraying. Wear appropriate protective equipment during application. Use a spray type that remains on the surface of the sprayed objects (e.g. suspension concentrate or micro-encapsulations) so as much of the substance as possible will come into contact with the bed bugs. Ventilate rooms well before use and vacuum and clean any dead insects and unwanted insecticide residues. The poison can attach to dust and small particles so limit inhalation by using appropriate respiratory protection during cleaning.
After treatment is completed, be alert for any recurrence of bed bugs. Make regular inspections over a longer period. Look out for live bed bugs and any new bites.