If you have arachnophobia, you will want this, particularly because it can block out images that can appear without warning when using social media or photography/wallpaper sites.

How well it works is site-dependent. It works superbly on blogs and places like Wikipedia, where images of spiders tend to appear on pages that have a spider-related web page title/URL. It also works more consistently on sites that are more consistent with using alt text, including automatically generated alt text, because said alt text will usually have a spider-related word.

This extension won't work perfectly everywhere but it does overall greatly limit the spider-related images that do get shown...but you can still be surprised depending on what sites you browse.

The main downside is there are false positives when it comes to images of the superhero Spider-Man and related series and characters.

Have not tested to see how this extension handles images based on other arachnoid characters such as Shelob from LOTR, Aragog from Harry Potter and the Chamber of Secrets and the various species names in various fantasy works for spiders that aren't just called spiders.

Ideally, this extension would have a means to add additional names to the filterlist and to have a whitelist (such as to cover Spider-Man).

Still, this extension as-is a great safeguard for those who have arachnophobia.