This should happen if, and only if, the same "remove it, it bothers me" option is available for every single phobia on http://phobialist.com/, bar none- not just for arachnophobics.
The only threads we've had on these forums concerning phobias have been related to spiders (but I would guess the people who fear spiders would fear other arachnids, as well), so... why should we help with all of those you listed? We've had many topics about arachnophobia and pleas to allow an option to hide spiders, but not any other phobia. I'm going to hazard a guess that in-game arachnids are the most disliked of all digital... anything, really, simply because of how many people seem concerned about it. Personally, I don't think allowing a setting option to get rid of them would be all too difficult and I'm sure an option for those with arachnophobia would be beneficial to more people than options catering to any other phobia. I very strongly believe that would be the case from what I have witnessed on these forums.
To all of you berating and picking on the OP for his phobia, get over yourselves and stop being selfish, inconsiderate jerks. I used to think these forums were generally more well-behaved than other internet sites, but sheer ignorance in relation to what a phobia actually is that I've witnessed across these threads are both surprising and infuriating. It doesn't make you look cool. If you disagree with an option to replace in-game arachnids with something else, that's fine, but you don't need to be a donkey about it.