They show up individually in the most bizarre places. Sometimes, they attack in swarms. Maybe they are pesky for both of those reasons. It's quite common.
Helpful critters can often become pests.
It seems to be true when few and not many want them around. Especially if you are an aphid, garden pest, or snake who relies on other's misfortunes for sustenance. It happens all the time, but when it happens in your community, in your school, home or back yard, it's much more troublesome. Some people think they are kind of cute. Others pay no attention.