Scary little critters. They suddenly appear, sometimes in large groups, and the only way to get rid of them or diminish their effect is to start a support group, donation drive or similar. If you are pestered by a really nasty one, it crawls up your spine and pins its spiky legs in your spinal cord. The are a very human sign and actually a good one. But some humans get aggressive and try to erase the mishap by killing, hurting, looking away or denouncing the victims.
How to fight it
One of the monsters where actually being nice, actually following your conscience and not listening to the mass is the best way to avoid it. I heard, that an ethical fly swapper helps as well but leaves nasty marks.gab