The human louse, Pediculus humanus. P.19. The louse sucks blood through contact. There are two species of human lice: the head louse, Pediculus humanus capitis, which lives in the scalp hair and the body louse, Phcorporis, which lives on the body and clothes.

The crab louse, Phthirus pubis. P.3. The crab louse sucks blood and lives in the body hair of humans, especially on the abdomen. The crab louse is transmitted by intimate contact.

The bed bug, Cimex lectularius. P.41. The bed bug feed on human blood, which they suck from us at night. They are found in heated homes and are transmitted when infested house hold effect are moved.

The human flea, Pulex irritans. P.92. It is found in moist, dirty houses. It sucks blood from humans. It is rare and is transmitted by transfer of adult fleas and when moving infested household effects.

There are two species of follicle mites, Demodex folliculorum and Demodex brevis. P.123. They live in hair follicles, especially on the nose, feed on sebum and rarely causes symptoms. They are transmitted by body contact.

The itch mite, Sarcoptes scabiei. P.115. The itch mites feed on the top layer of the skin. They are especially found between fingers and on wrists. The itch mites are transmitted by intimate contact.

Physical methods

Heat treatment. All stages of insects are relatively vulnerable to high temperatures. If it rises just a few degrees above the optimum temperature, development stops and harmful effects occur. Coming up around 50 degrees Celsius the heat kills in a short time. Heat treatment is therefore an obvious control method. Less suspicious effects can be treated in an incubator for example. Just an hour at 50 degrees Celsius will suffice. Of course, it must be made sure that things get thoroughly hot during this period. Heating of rooms may be an option. Here the temperature has to be kept at 50 degrees for at least 12 hours, and attention should be paid to the fact the animals possibly will take refuge in cool crevices. The method is not without problems, and temperature sensors should in all cases be placed at strategic locations.

Cold treatment. As mentioned, bed bugs are sensitive to low temperatures. Normal deep freezer temperatures -18 to -20 degrees Celsius kill them within 3-4 days. It is a reasonable method for treating small batches of suspicious effects when it has been ensured that they can tolerate this treatment.

Non-toxic dusts. Diatomaceous earth and other fine-grained mineral soils have been used for insect control since ancient times. The “Romans” mixed fine road dust in the grain to be stored. Diatomaceous earth acts primarily by destroying the waxy layer that protects the insects from drying out. The effect is relatively slow. The insects die within a week due to water loss. In turn, this dust keeps its effects almost infinitely, if kept dry. Diatomaceous earth is suitable for treating inaccessible cavities and crevices, which can serve as strongholds for the insects.

Modified atmospheres. The principle consists in replacing the ordinary atmospheric air with an air, which is oxygen deficient and contains large amounts of nitrogen or carbon dioxide. In the long run, insects cannot live in an oxygen deficient atmosphere, but the treatment requires a lot of time, often weeks to be effective, something that requires the method to be used in fully sealed containers. Bed bugs are not particularly sensitive to nitrogen, but carbon dioxide has a direct toxic effect like heat and pressure can reduce treatment time significantly.

Biological control. Biological control where the pests’ natural enemies are actively used is a recognized method against many pests in agriculture and forestry. Bed bugs have some natural enemies, the assassin bug (page xx) among others, but their natural amount will never be such that they play a practical role, and the release of large amounts of these reduviids in Danish homes is obviously not an acceptable method of keeping bed bugs at bay.

Development of adult bed bugs

Bed bug leaves egg

Fig. 18. When the bed bug nymph leaves the egg, it pumps liquid into the head and wiggles its way out using peristaltic movements. (Askew)

Insects cannot grow gradually; their exoskeleton simply prevents it. Therefore, they must grow in stages, changing skin sometimes in the course of development and growing a size each time. The insects’ development can proceed in two radically different ways. Some insects undergo a complete metamorphosis. A good example is butterflies, where out of the egg comes a caterpillar that in no way resembles the adult. It must undergo a pupal stage where the complete metamorphosis to adult butterfly takes place.

In others, and among them the bed bugs, the little bugs that come out of the eggs broadly resemble the adults. They undergo an incomplete metamorphosis. In case of the bed bug, it goes through five nymphal stages (fig 18); they grow bigger for each molt and resemble the adults more and more.

The bed bug nymphs must have a blood meal between each molt.


Bed bug mating behavior is something else. The male does not inseminate the female’s genital opening directly, as with other insects. His genital organ is transformed into a kind of hypodermic needle that can pierce the female’s exoskeleton and ejaculates the sperm directly into her abdomen. It is quite a violent process that looks more like a murder attempt than mating, and in technical terms it is called traumatic insemination. The injected sperm travel via the blood. In these insects it does not run in the veins, but washes freely around the organs. The sperm end up in a couple of pouches on the female’s oviducts, called spermathecae. Here they remain viable as long as the body temperature is normal and there are plenty to fertilize all the eggs the female lays in its lifetime.

There is nothing to suggest that the two sexes can recognize each other from appearance, special pheromones or behavior. A male in rut will attempt to mate with other bugs of a certain size and that has just sucked blood. This means that it will also attempt to mate with other males. However, a complete mating with other males is in almost all cases prevented. This is done by a particular fragrance, an alarm pheromone, being released by the harassed male. Like many other insects, bed bugs can communicate by using specific pheromones. The pheromones are released from special scent glands in specific situations, and can trigger a specific behavior in similar species. Among other things, bed bugs can make use of an alarm pheromone when they are in danger. It deters the bed bugs that are nearby, causing them to spread out so they do not all become an easy prey for a predator. This pheromone is quite volatile, and soon the bed bugs get back together.

It has been found that a male bed bug in danger of rape emits this deterrent alarm pheromone. In most cases, it will cause the male in rut to refrain from completing the process.

If the opportunity presents itself, the common bed bug will mate with the bat bug (Cimex hemipterus), but the eggs are usually sterile.

Can you recognize a bed bug bite?

There are big differences in people’s sensitivity to bed bug bites. Some, about 10% of the Danish population have no reaction at all. This means that they can donate blood to a large population of bed bugs without noticing it, and maybe only discover the animals later by accident. In most people, the bed bug bites leave red itchy spots, an allergic reaction to the foreign proteins in the bed bug’s saliva.

Exactly because people react so differently to insect bites, it is difficult, if not impossible, to immediately distinguish one kind of itchy rash from the other, and the matter is further complicated by the fact that the bites can be mistaken for skin reactions due to hypersensitivity.

To get an idea you must take into consideration whether you are bitten indoors or outdoors, what time of day it happens and where on the body the clues appear. If you get bitten at night, on exposed parts of the body, maybe in a hotel room, there is a high probability that it is from bed bugs, but it could also be from mosquitoes. If a few fleas have gotten into the bed, they will mainly bite underneath the clothing, preferably where it fits tightly, or they bite where the body has been in contact with the foundation, since they would like to push back when they have to pierce the proboscis into the skin.

Bed bugs

Bedbug, male

Bedbug, male

Three things hurt in a peasant’s house: “Mean wife, smoke and bed bug” (Peder Syv, approx. 1680)

Bed bug in satire drawing

Fig. 16. A common bed bug dreaming of the old days. (Usinger)

Where in the system do bed bugs belong?
Bed bugs are insects and therefore belong to the largest class of living animals. Currently, about 1 million different species of insects have been described and it is expected that there are 10 million or more, still unknown. Among other things, the insects are characteristic of having an exoskeleton, as armor around the intestines. The body is divided into three sections: 1) the head with mouth parts, antennae and eyes 2) thorax with three pairs of legs and usually two pairs of wings 3) and an articulated abdomen.

The bed bugs are true bugs (Heteroptera) .The mouth parts of the bugs form an effective, sharp proboscis, which most use to suck sap. The vast majority of bugs have two pairs of wings, so also in this way the bed bugs stand out, being wingless bloodsuckers. The common bed bug (Cimex lectularius) is, along with other bed bugs, considered as their own little family: Cimicidae.

Bed bug

Bed bug

Bed bug

(Latin: Cimex lectularius)

Unlike most other bugs, the bed bug is wingless. When it has not recently fed its body is paper-thin, and almost red-brown. So far as is known bed bugs originated from Asia, but they have now spread to all parts of the world. They were well known in ancient times in the Mediterranean area. As they require a warm, dry climate they did not spread to northern regions until buildings started to be heated more or less efficiently, but when this did happen they soon became very abundant. They are now less common and are largely kept under control by modern insecticides.

Bed bugs only search for blood donors when they are actually hungry. In the intervals between meals they spend their time in suitable hiding places in the vicinity of the bed. This may be crevices in timber, joints in the bed, beneath loose carpeting, and behind pictures and wall- paper. When hungry, bed bugs come out from their retreat and start to search. Their senses are not capable of guiding them to a distant blood donor, but at distances of 5-10 cm they will be attracted by the body warmth of the victim.

Bed bugs can crawl up a wall and can also walk upside down on rough ceilings, but if they are not skilled they often fall down. This is the basis of stories that bed bugs, having observed that their victim had placed the legs of the bed in dishes of water, crawled up the wall and along the ceiling and let themselves fall on to the poor sleeping victim. However, the bed bug is not as crafty as this.

In the course of about 10 minutes an adult bed bug can suck up to 7 times its own weight in blood. It then retreats to its hiding place, where it digests, mates and lays eggs until it is hungry again.

The eggs are laid in the hiding place, where they are attached to the substrate. A female lays a total of 200 eggs, 4-5 per day, but the actual number depends upon the temperature and other external factors. They do not reproduce at all at temperatures below 10° C.

Young bed bugs are like small versions of the adults. They moult 5 times during their development and at each stage they require a new meal of blood.

Bed bugs can be controlled by thorough treatment of their hiding places with an insecticide.

Some of the vertebrates with which we more or less voluntarily share our homes are also attacked by other bugs which live in the vicinity of their nests or sleeping quarters. These bugs are often bed bugs. Sometimes they move about and enter houses, and in rare cases they may attack humans: