Humans are most comfortable with those things that resemble themselves, both in terms of physical features and mentality. A dog, for example, may have an extra set of legs and a tail, but does not differ all that significantly from humans or other mammals—we can similarly see ourselves in the behavior and apparent emotions they exhibit.

Arachnids, on the other hand, are several orders of magnitude more alien. Beyond the gross physical dissimilarities, it is impossible to attribute anything resembling human emotion or motivation to them. Add to that their penchant for appearing unexpected in dark places and inherently predatory nature, the very idea of spiders triggers in many people a primordial dread.

Humans are most comfortable with those things that resemble themselves, both in terms of physical features and mentality. A dog, for example, may have an extra set of legs and a tail, but does not differ all that significantly from humans or other mammals—we can similarly see ourselves in the behavior and apparent emotions they exhibit.

Arachnids, on the other hand, are several orders of magnitude more alien. Beyond the gross physical dissimilarities, it is impossible to attribute anything resembling human emotion or motivation to them. Add to that their penchant for appearing unexpected in dark places and their inherently predatory nature, the very idea of spiders triggers in many people a primordial dread.