Spider fear inflates size perception, highlighting the role of emotion in threat assessment

“Do we see what we feel?” A new study in Cognition & Emotion finds that people who fear spiders tend to overestimate their size, while spider experts are more accurate in their assessments.

Fear can shape the way we perceive the world. Numerous studies have shown that individuals with specific phobias tend to exaggerate threat-related features, such as overestimating the size or proximity of the feared object. In the case of spider phobia, research has consistently demonstrated that fearful individuals perceive spiders as larger than they actually are. This finding aligns with evolutionary theories suggesting that heightened perception of threats may aid in survival.

However, while fear-related perceptual biases are well-documented, less is known about whether people with expertise in a domain show similar distortions. Experts might be expected to be more accurate due to their knowledge, but some studies suggest they may still be biased, particularly when the stimulus is central to their field.

Yahel Dror Ben-Baruch and colleagues explored this question by directly comparing perceptual biases in three groups: spider-fearful individuals, spider experts, and control participants. Their goal was to understand how emotion (fear) and knowledge (expertise) interact in shaping perceptions of the size of spiders.

Importantly, while past research has examined each group in isolation, this study is the first to place them side by side in a single design. Participants were asked to estimate the size of spiders, wasps, and butterflies, allowing researchers to assess whether distortion was specific to spiders and whether it occurred across different levels of familiarity and emotional relevance.

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The final sample included 169 adults, aged 18–70, divided into three groups: 58 highly fearful of spiders, 59 spider experts, and 52 control participants. Spider-fearful and control participants were recruited via social media, while experts — defined as students in biology, ecology, zoology, entomology, or life sciences with formal coursework in arachnology — were contacted through targeted emails.

All participants completed the Spider Phobia Questionnaire (e.g., “I shudder when I think of a spider”), with high scorers assigned to the fearful group and low scorers to the control or expert group. Anyone with a high fear of butterflies or wasps was excluded to isolate spider-specific effects.

Participants completed the study online via Qualtrics. They viewed 90 images — 30 each of spiders, butterflies, and wasps — standardized in display size but varied by species. In the size estimation task, participants rated the real-life size of each animal on a visual scale from 0 to 100, where 0 represented the size of a fly.

A separate task asked participants to rate how unpleasant they found each animal on a scale from -100 (very pleasant) to 100 (very unpleasant). Unpleasantness was measured to differentiate fear-based responses from general discomfort. The actual size of each species was recorded by a co-author (Y.Z.), a trained entomologist, allowing researchers to assess the accuracy of size perceptions.

Participants fearful of spiders significantly overestimated the size of spiders compared to butterflies, despite the actual spiders being smaller. On average, they rated spiders as 1.17 times larger than butterflies and 1.80 times larger than wasps. In contrast, the expert group accurately rated butterflies as larger than spiders, aligning with actual species measurements. The control group rated spiders and butterflies as nearly equal in size, an inaccurate perception given that the butterflies were objectively larger.

Unpleasantness ratings revealed that the spider-fearful group found spiders far more unpleasant than the other insects, consistent with their phobic status. The control group also rated spiders as more unpleasant than butterflies or wasps, though to a lesser degree.

Experts reported low levels of unpleasantness across all insects, reflecting emotional neutrality. Interestingly, although wasps were also considered threatening, they were not overestimated in size by any group. This suggests that size distortion is not simply a function of threat or unpleasantness, but the combined result of threat and personal relevance — such as the fear of spiders.

One limitation is that conducting the experiment online may have introduced variability in screen display that could affect perceived size. However, this was mitigated by using a mental anchor (the size of a fly) rather than relying on an on-screen reference.

Overall, this study demonstrates that emotional fear, not just threat, can distort how people perceive the size of objects, while expertise may help maintain perceptual accuracy.

The research “Do we see what we feel? A comparative study of spider size estimation among experts and people who are highly fearful of spiders,” was authored by Yahel Dror Ben-Baruch, Yoram Zvik, and Noga Cohen.