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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 treated 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 excessive fear of arthropods like insects and spiders. Entomophobia ("entomo" = insect + "phobia" = fear) refers to an unreasonable fear of real arthropods. The key here is that the fear involves a real stimulus such as an insect or spider, encountered in everyday activities. For example, a spider might trigger this intense fear. The good news is that entomophobia is highly treatable and generally only a significant concern if it limits someone's everyday activities.

On the other hand, there's a much more serious condition called delusions of parasitosis (DOP), which causes a severe and debilitating reaction to an imagined (not real) infestation. In general delusions are false beliefs 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 additional signs 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)

  • believes bites or skin lesions are from unknown or unseen causes
  • believes that home or workplace are "infested", in addition to a "personal infestation"
  • reports having resorted to self-treatment with insecticides or other harsh chemicals (bleach, kerosene)
  • has fear for others "becoming infested" which leads to self-imposed isolation
  • has had multiple, unsatisfactory contacts with the medical or pest control community
  • may have abandoned home 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 - This file contains references to DOP from the scientific literature compiled in 1997.

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


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Jack DeAngelis, Ph.D.

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