Entomophobia is a specific phobia characterized by an excessive or unrealistic fear of one or more classes of insect, and classified as a phobia by the DSM-5. More specific cases included apiphobia (fear of bees), myrmecophobia (fear of ants), and lepidopterophobia (fear of moths and butterflies). One book claims 6% of all US inhabitants have this phobia.
Lepidopterophobia can be developed in some ways. One of them by having a scary experience or if the person believes that the insect is dangerous. For example, if the person thinks a butterfly is venomous, he/she will do anything they can to avoid getting close to them.
Entomophobia may develop after the person has had a traumatic experience with the insect(s) in question. It may develop early or later in life and is quite common among the animal phobias. Typically one has from a fear from one specific type of insect, and entomophobia leads to behavioral changes: the person with entomophobia will avoid situations where they may encounter the specific type of insect. Cognitive behavioral therapy is considered an effective treatment.