Insect stings while bike riding
It happened twice to me to be stung:


once a wasp entered from the neck under my loose shirt, and being trapped between the fabric and my chest didn't find anything better than stinging me.
another time I was cycling along the coast and felt a sudden burn between my thumb and my pointing finger. Something stingy was there and had the idea of sticking its harpoon into my flesh.


And if we don't consider stinging but insect accident in general...


another time, while I was speeding downhill, a bumblebee loaded with pollen splashed onto my glasses. Not painful for me, but my face was half covered with a yellowish goo.
while panting for a climb, some mosquito decided that my mouth was a nice place to rest (forever)


Now, I ride for more than 30 years, so I would dare to say, based on my sole experience, that mishap with insect are rare but can happen, and if they feel threatened they fight back.

Wear tight shirt to avoid them being trapped between the clothing and your skin, keep your mouth closed as much as possible, and wear glasses to protect your eyes. That should do for most of the cases.