Why is everyone afraid of spiders?
Even the big poison ones. :\
It's a rational fear, and it's likely something that's been drilled into our human minds from survival.
It's the small insects that can cause the most damage to you.
Sure, you can kill all the lions and fight off all the tigers, but that little six or eight legged crawling thing can sneak on you and have you dead in not long at all.
Besides, lots of insects and bugs and things like that, ants and wasps in particular, are known for swarming.
What's worse than being bitten or stung by an ant or wasp? Being bittern or stung by thousands of ants or wasps.