LogFAQs > #907211084

Licensed pest control technician, reporting in.

Those are bald-faced hornets. And yeah they're incredibly aggressive. Whether you should eliminate them honestly depends on how in the way they are.

If the nest is hanging like, only 7 or 8 feet in the air, and it's close to your walkway, then you might want to consider calling a company to get rid of it.
If it's more like 10 feet or more up in the air, people walking on the ground will be far enough away from their flight path that they won't present much of a problem. We're deep into wasp/hornet season, so if it's only the size of a soccer ball now, it won't get too much bigger and they'll probably die off by November. (And no, they won't get nastier the later in the year it gets as one poster said. The cooler the weather gets, the less aggressive they'll be since they can't move as fast or fly as well when it's colder)

Whatever you do, do NOT try and knock it down or treat it yourself, even at night. A nest that size will contain several hundred of them, and they don't fuck around if they think their home is in danger. The only way to destroy it is by chopping it open, spraying it down on the inside so that the entirety of the nest is soaked with pesticide, and the queen is killed. Spraying wasp freeze on the outside will kill some, but it won't get rid of the nest, and just knocking the nest down is going to make them even more aggressive than they already are.
Also, other mistruth floating around this topic, there's always going to be hornets inside. There's no point where they all just leave, and it's safe to go after them.

tl;dr if it's far enough up in the tree that they're not going after you or anyone, just ignore it and they'll clear out in like 3 months. If it's close to eye level, near a walkway, call a pro. Don't try it yourself.
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AKA Level 36 ForestWanderer
-Revenant Dracanea-