Arachnophobia is a specific phobia, an abnormal fear of spiders and sometimes other arachnids, such as scorpions and harvestmen.

It is among the most common of all phobias. The reactions of arachnophobics often seem irrational to others (and sometimes to the sufferers themselves). People with arachnophobia tend to feel uneasy in any area they believe could harbor spiders or that has visible signs of their presence, such as webs. If they see a spider they may not enter the general vicinity until they have overcome the panic attack that is often associated with their phobia. They may feel humiliated if such episodes happen in the presence of peers or family members.

The fear of spiders can be treated by any of the general techniques suggested for specific phobias.

Arachnophobia is, in many cases, the result of a traumatizing encounter with spiders in one’s early childhood, though the experience may not be remembered[citation needed]. An evolutionary reason for the phobias, such as arachnophobia, claustrophobia, fear of snakes or mice, etc. remains unresolved. One view, especially held in evolutionary psychology, is that the presence of venomous spiders led to the evolution of an innate fear of spiders or made acquisition of a fear of spiders especially easy. Like all traits, there is variability in the intensity of fears of spiders, and those with more intense fears are classified as phobic. Spiders, for instance, being relatively small, don’t fit the usual criterion for a threat in the animal kingdom where size is a factor, but most species are venomous (although many of the poisons produced by these species having no effect on humans), and some are lethal. Arachnophobics will spare no effort to make sure that their whereabouts are spider-free, hence they would have had a reduced risk of being bitten in ancestral environments. Therefore, arachnophobics may possess a slight advantage over arachnophobics in terms of survival. However this theory is undermined by the disproportional fear of spiders in comparison to other, far more deadly creatures that were present during Homo sapiens’ environment of evolutionary adaptability

The alternative view is that the dangers, such as from spiders, are overrated and not sufficient to influence evolution. Instead, inheriting phobias would have restrictive and debilitating effects upon survival, rather than being an aid. For example, there are no deadly spiders native to central and northern Europe that could exert an evolutionary pressure, yet that is where the strongest fear for spiders began, suggesting cultural learning. In contrast, many non-European cultures generally do not fear spiders, and for some communities such as in Papua New Guinea and South America, spiders are included in traditional foods.