Arachnophobia

Arachnophobia is an unmarked quest

Walkthrough
During the quest We Will All Go Together, the player will eventually find Private Kyle Edwards who has one of the dogtags needed to complete the quest, with one of the options to retrieve his dogtag leading to this quest.

It can also be suggested that Edwards go somewhere else, and he can then be prodded into revealing that he is hiding due to a fear of radscorpions.
 * Lie to Edwards about having killed all the radscorpions. Thinking it is safe to leave, Edwards will depart, but radscorpions will spawn outside the house and attack him. Acquiring the dogtags via conversation will no longer be possible. Once the player leaves the house, Edwards' corpse will be close by and three giant radscorpions will attack. Gain 60 XP and loss of Karma for this action.
 * Volunteer to kill the radscorpions for Edwards, then head outside. Radscorpions will spawn and likely attack; killing all of them and reporting back to Edwards will allow the player to suggest that Edwards no longer needs his dogtags, since he is now free to go. He will agree and hand them over.

After the radscorpions are eliminated, Edwards will still not leave until the player finds him a place to go. The following options are available to accomplish this:
 * Tell him that there are plenty of places in the Wasteland. He will agree and leave, and no Karma change will occur.
 * Suggest that Astor might take him back in, leading to the following options:
 * Lie, telling him that Astor would be happy to see him unexpectedly. This will result in a loss of Karma, and Edwards will run to the NCR camp. The NCR patrols in the area will then likely gun him down, as they are operating under the assumption that all ghouls coming from Searchlight are feral.
 * Offer to return to Astor and explain Edwards' predicament. This will allow the player to now do the following after explaining to Astor that Edwards is not feral:
 * Suggest that Edwards can be of help. Astor will agree to take him in.
 * Explain that Edwards is not showing any signs of going feral. Astor will agree to take him in.
 * Ask Astor to suggest a place for Edwards to go. Astor will mention a ranger station to the north that is run by ghouls, and will give the player the map marker for Ranger Station Echo.

Either of the outcomes chosen by the player in conversation with Astor will result in a Karma gain and Edwards leaving the house. If Astor is convinced to take Edwards back into his squad, Edwards will also give the player 50 caps for helping him reclaim his former life.