6

I feel like 1/2+ε is enough for the 3 spider case. The spiders can start (or take their sweet time to get) in this configuration: And then the two slow spiders can follow the red arrows to ensure the ant will be trapped, while the "fast" spider keeps watch on its edge. Unless I overlooked something, this seems to work, but doesn't prove there isn'...


3

Here is a strategy giving a better uppper-bound for the 3 spider case. And there is a strategy for two spiders, one with speed exactly 1 and one with speed ε.


1

A couple of words are confusing: By "hover" I assume you mean it's moving (generally means to stay in place) By "retain" I assume you mean some kind of average speed needed. Clearly our speed will accelerate and not be maintained as a constant. So, maybe:


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