This research aimed to investigate habituation to spider images during an online exposure treatment (www.feardrop.com) among participants with a high fear of spiders. Participants (N = 392) undertook a 10-stage online exposure treatment with a stage length of either 180 or 360 seconds. Four Subjective Units of Distress Scale (SUDS) ratings were taken throughout each stage. Treatment completion was found to be a significant challenge, with less than one-third (30%) completing at least one stage of the program. Those in the shorter stage length condition were significantly more likely to complete the first stage relative to those in the longer stage length condition (43% vs. 16%). SUDS ratings decreased significantly across time at Stage 1, suggesting habituation of self-reported anxiety and there was an overall reduction in SUDS ratings at the second relative to the first stage, suggesting generalisation of habituation. The greatest habituation was observed among those with high anticipatory anxiety (pre-exposure SUDS rating), high total exposure time, and younger age. There was preliminary evidence for improvement in symptoms of spider fear at post-treatment. Directions for future research include strategies to facilitate treatment completion, evaluation of treatment outcomes, and expansion to include a range of specific fears.