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 Phobias & Delusions

- Help is available but the most important thing is to recognize the problem -

Summary: Phobias and delusions can be mild to serious psychological disorders that should normally be dealt with by the medical community. In cases where insects, mites or "bugs" are involved, entomologists are sometimes asked to investigate.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

Difference between delusion & phobia

Two different conditions are recognized that relate to an inordinate fear of arthropods like insects and spiders. Entomophobia ("entomo" = insect + "phobia" = fear) refers to an unreasonable fear of real arthropods. The key here, as with other phobias, is that the fear involves a real stimulus, in this case an insect or spider, encountered in everyday activities. For example, a spider found inside the home might trigger this intense fear reaction. The good news is that entomophobia is highly treatable with desensitization therapy and generally only a significant concern if it limits someone's everyday activities.

A condition called delusions of parasitosis (DOP), or delusional parasitosis, on the other hand, is a severe, debilitating reaction to an imagined infestation. Delusions are a mistaken belief and in this case the person believes, wrongly, that they are infested with an insect or mite, or that they are being repeatedly bitten (see signs of DOP below).

garden spider

A harmless garden spider can provoke irrational fear in some people.


The mistaken belief, or delusion, can be triggered by something as simple as an allergic reaction, a chemical sensitivity, emotional stress or even recreational drug use. As with other delusional disorders, professional psychological counseling is generally needed. See this UC Davis site for clinical definitions and treatment suggestions.

Entomologists are sometimes asked to investigate cases of mysterious bites that may or may not have physical manifestations such as skin lesions. These cases generally fall into two broad groups.

Most are some type of "mistaken identity" in which the person believes that some harmless insect or spider is biting/stinging them. Usually any associated skin irritation has an environmental explanation. In a small percentage are cases, however, the person has an unshakable belief that they are infested with an unseen "bug" and all attempts to find and identify the culprit have failed.


All such complaints should at least initially be investigated with the underlying assumption that a real arthropod infestation is present. There are a number of insects and mites that can cause real skin reactions and lesions (see Causes of Mysterious Bug Bites for a list of some real culprits). For example, bird/rodent/nest mites cause bites that can be very difficult to diagnose (see Bird Mite Bites). The following signs, however, are indicative of imagined infestations in my experience:

Signs of DOP (this is my own list and is probably not exhaustive)

  • reports bites or skin lesions from unknown causes
  • reports they alone are being bitten or, interestingly, close family members also "infested"
  • reports that home or workplace "infested", in addition to a "personal infestation"
  • reports resorting to self-treatment with insecticides or other harsh chemicals (bleach, kerosene)
  • reports fear for others "becoming infested" which leads to self-imposed isolation
  • reports multiple, unsatisfactory contacts with the medical or pest control community
  • reports that home has been abandoned because of the "infestation"
  • reports that "bugs" are invisible or disappear after capture
  • submits elaborately wrapped samples, often with very detailed collection information
  • submits samples of body tissue or swabs

Related Articles

[Delusions of Parasitosis (pdf)] - This file contains references to DOP from the scientific literature compiled in 1997.

[Mites That Bite Guide (pdf)] - There are a number of very small mites that actually bite and cause skin lesions. These causes must be excluded before a diagnosis of delusions can be made.


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