There are thousands of species of bugs. The vast majority do not affect humans. Most are pests. But there are bugs that act as direct or mechanical vectors of parasites. And still others, that while are not known to transmit diseases, are important in the psychological and sometimes physical toll that they incur on their host as ectoparasites. We will discuss the more important bugs as they relate to parasitology.

Bedbugs (Cimex lectularius)

Bed bugs (Cimex lectularius) are nocturnal bugs that feed on the blood of their hosts. They are lay hidden during the day in crevices and cracks of walls, furniture, and floors. They are drawn to the CO2 of their sleeping unsuspecting hosts. The saliva placed at the bite site acts as an anesthetic to lessen the pain of the piercing of the skin to obtain the blood meal. In most individuals the saliva acts as an allergen and produces intense itching at the feeding site. Though the bugs are not known to transmit any parasitic or bacterial infections, the sites of irritation can become secondarily infected with bacteria; some infestations can be so heavy that the individuals being fed on can develop anemia resulting in weakness / lethargy ; and lastly infestations can produce insomnia and lead to a decrease in the functional quality of life for the host.

Bed Bug (Cimex lectularius) – this is a photo of a Bed bug that has recently fed. Normally the bug has a more round to oval shape. The blood meal gives the bedbug this elongated shape. Photo by W. Vientos

Once established in an environment bed bugs can be difficult to eradicate and may require the services of an expert exterminator. Repeat visits of an exterminator or treatments may be needed to completely eradicate them. Specially trained dogs are many times employed to search for hidden hard to reach colonies that make their eradication difficult.

Though relatively thought of as an infestation seen in the homeless shelters, jails or other crowded institutions, bedbugs can be a big problem in the hotel business where infestations can occur. Hotels can also be a bridge to bringing the bugs to your home. A website committed to the communication and warning of hotels that are known or have been sited for Bedbug infestations is the following:


Typically a bed bug is 0.18 inches in size or the size of an apple seed. Juvenile bed bugs can range from the size of 0.09 inches. Normally these go undetected. The presence of red/brown rusty stains and material on bedding is a sign of bed bug infestation along with trailing bite marks on the legs, arms, and abdominal area that are itchy.

Bed Bug (Cimex lectularius) – this bug is an example of a bug that has not fed and is normally the stage of bug observed. They are round to oval, heavily segmented, dark brown.
Photo by W. Vientos
Photo by W. Vientos
Bed bug sitting comfortably on the clothing fibers of a homeless man that was infested with bed bugs. Though commonly thought of as residing in the cracks of walls, furniture, etc… humans can also act as a site to reside on and conveniently move to feed on the host – Photo by W. Vientos
Bed bug nymph – these nymphs are difficult to see many times because of their small size and translucent coloring. This particular nymph, spotted by an astute nurse, was crawling on the bed of a patient being prepared for an outpatient surgical procedure and sent to the laboratory for identification – Photo by W. Vientos
Bed Bug (Cimex lectularius) – this bug is an example of a bug that has not fed and is normally the stage of bug observed. They are round to oval, heavily segmented, dark brown.
Video by W. Vientos

Life Cycle of the BedBug

The are total of 7 stages in the life cycle of the Bedbug.

Triatomine bugs (Reduvid Bug, Assassin Bug, Cone Nose Bug, Kissing Bug)

Triatominae species bug (photo courtesy of CDC)

The Reduviidae are a large group of bugs that are geographically widely distributed. The Triatomine bugs are a type of Reduvid bug that is medically important as the vector of the hemoflagellate, Trypanosoma cruzi. Trypanosoma cruzi causes Chaga’s Disease in humans.

The bugs are nocturnal in their feeding habits. They will use cracks in buildings to dwell in during the daylight hours. Prime dwellings for this arthropod can be found in adobe brick type houses and thatched roof type houses. But any housing poorly constructed can provide safe dwellings for these bugs. They will locate themselves relatively close to their food source, the blood of humans or other animals. At night they venture out attracted by the CO2, warmth, and moisture of the host. The high concentration of CO2 around the facial area will result in most bites occurring around the facial area. Interestingly, as the bug is taking its blood meal it also defecates. This is an important characteristic in that the bug’s feces will contain the infectious stage of Trypanosoma cruzi. The site of the bite will produce irritation that will cause the host to scratch the site and in so doing introduce the parasite into the bite wound.


The cockroach is an important vector of bacterial, viral, and parasitic diseases via mechanical transmission. There are many species, with varying sizes and preferred habitats. The German cockroach is perhaps the most common. They are nocturnal, usually scattering when a dwelling is lit. They have an indiscriminate taste for a variety of food sources. House infestations are difficult to control or eradicate and are generally more common in areas where there is overcrowding and a lower socioeconomic population.

German cockroach ( Blattella germanica) – most common of the cockroaches is about 1.1 to 1.6cm in length.
Illustration by W. Vientos