Bed bugs are certainly annoying. They cause numerous bites that can itch, burn, swell, or cause severe allergic reactions. They’ve caused anemia, insomnia, and psychological stress in their victims. But are bed bugs considered parasites by the scientific world? This is a common question that we hear, and the answer comes from an interesting inspection of bed bug entomology.
What is a parasite?
To answer whether or not you could consider bed bugs a parasite, we first need to cover what a parasite actually is. When most people hear the term, they think of tiny worms or other organisms in your body, feeding out of sight and causing all sorts of serious illnesses. However, that example only describes one kind of parasitic behavior.
Put simply, a parasite is an organism that benefits at the expense of another organism. Of course, by that broad definition, many animals could be considered a parasite. If we kill cattle and eat them for sustenance, doesn’t that make us a parasite, since we benefit at the cattle’s expense?
Ecological studies already have a term for that sort of relationship: humans killing cattle are predators, and the cows are the prey. The main distinction between parasites and predators is that the relationship doesn’t begin with, nor depend on, the parasite killing their host. The relationship is also not always exclusive to dietary needs: the host could be providing the parasite with any number of perks, such as food, protection against predators, or even a method of reproduction.
Biologists usually classify parasites based on their dependence on a single host. This is called a parasitic relationship, and is considered a form of symbiosis (a fancy term for an ecological relationship between organisms). Parasitism is a bigger part of our ecology than most people realize — it’s more common than all other feeding methods combined! It’s estimated that more than half of the world’s animals are parasites at some point in their life. Humans alone are hosts to hundreds of different parasitic species.
So are bed bugs considered parasites?
In short: yes! Bed bugs fit the definition: they depend on a host to survive, and the host does not benefit from the relationship. More specifically, bed bugs would be considered an ectoparasite, since they exist outside of the host rather than inside of it. This classification is similar to fleas, ticks, or leaches, though bed bugs spend a very small portion of their life in direct contact with their host; they most often feed and then retreat to some hiding place in the room.
A human head louse, another common example of a social ectoparasite. Photo credit: Gilles San Martin
Bed bugs could also be considered social parasites, since they take advantage of the social interaction of their host. Bed bugs depend on humans traveling and converging in common areas (such as airports, offices, and hotels) in order for them to travel and spread from host to host. The term “social parasite” could mean many things, from a bed bug hitch-hiking on a person’s luggage to cuckoos tricking other birds into raising their hatchlings (which is a fascinating subject, by the way).
Bed bugs display many ecological traits that are common among parasitic species, such as wide dispersal of fertile females, inbreeding among offspring of a single female, and highly specialized adaptations for living with humans. Evidence suggests that bed bugs have been feeding almost exclusively on humans for thousands of years, dating back to when humans first left their caves and bed bugs and bat bugs evolved from their common ancestor.
It’s important to note that just because bed bugs are a parasite does not mean that they are severely harmful. While certain parasitic organisms are very serious (malaria is the most common parasite to kill its human host), bed bugs are not known to transmit disease, and their host won’t be killed by the relationship. They simply benefit at our expense by feeding on our blood, leaving behind irritating bites and sometimes causing anemia, insomnia, and other conditions.
What does all of this mean? It means that bed bugs are really good at living with us. Over countless generations, they have gained tools through rapid evolution that help them travel with us, feed on us, and avoid being killed by us. Recently, they have even developed resistances to insecticides that nearly wiped them out. Their parasitic nature is why they have become so prevalent, and why they may never be eradicated.