Currently there are a few ways to pick spiders for Webber:
1. Use trap; spiders loose loyalty that way.
2. Make spiders to fall asleep via different means and pick them. Panflute and napsack work, but are too expensive fot the benefit they provide in this case, while dismissing spiders and waiting until day is clearly just workaround of the fact, that loyal spiders don't fall asleep during day, is unintuitive, and doesn't work if server has no day (and it seems to me that Webber's ability to take followers with him is one of his major unique upsides, therefore I'd like this tool to remain in hands of player even in lights out worlds and the like).
I suggest to make spiders fall asleep if they are in range of player who uses one-man band. Aside from being cute thing Webber can do to his followers, in terms of balance I think it's fair: it would require to use 1 more inventory slot for carrying one-man band, item has it's cost, is locked behind tier 1 magic, and one-man band could use one more useful effect. I'm not sure whether this item in hands of other players should be allowed to induce such effect since it would make spiders easier to deal with, but I personally think that it would be fun strategy, I appreciate strategies variety, so it would be ok in my opinion.
Another thing I'd like to suggest is to make spiders stackable in the inventory, provided they are of one type and loyalty state (loyal or neutral). Spiders rely on numbers, so Webber needs quite a few spiders to do something useful and effective, often he needs to lock at least 1 inventory slot for whistle to manage that crowd, at least 1 for item allowing to carry spiders (panflute, napsack, shoo-box+meat (2 slots) or grass+twigs+meat (3 extra slots!) for trap strategy), and currently can bring all of his followers with him into another shard, it just would require several travels between shards (especially when Webber returns with loot to base with his followers and needs to switch shards, but doesn't have spare 10+ inventory slots). Webber would likely use more than 1 type of spiders anyway (and that is at least 4+ inventory slots he needs to lock for spider shenanigans), and right now he already can carry them one by one from forest to caves and vise versa, spiders are useful only outside of inventory, so it would just remove tedium of the process.