I feel like I might be able to reason with a spider (however remote that possibility might be). At least predators have at least a little ability to reason. Maybe, just maybe, they'll decide that I'm more trouble than I'm worth. Spiders also seem unlikely to team up. You're maybe dealing with a couple competing to win Spider-Man's favor, but I'd not expect them to cooperate.
On the other hand, dealing with ants would be like fighting a fast unreasoning zombie horde, a literal flood of nashing venomous mandibles and with a singular, laser focused, drive to do violence. All they know is violence to achieve their queen's (Antman's) goal at any cost to any particular individual. That is MUCH scarier to me.