Giant Wasp

A giant wasp on the party's side is a stretch. The likely framings are a druid's animal companion or wild shape, a beastmaster ranger's bound mount-sized terror, or a swarm-keeper alchemist who has chemically tagged this specific hive. Lean on the bonded-handler framing, because nothing about Int 1 supports independent loyalty.

In combat the wasp is a flying spotter and harasser. Its 50 ft. fly speed beats most ground enemies' chase, and an aerial wasp with 22 HP can sit ten feet above an archer and dive whenever the handler points. Use it for distraction and angle: a wasp diving at an enemy caster forces them to think about their face instead of the spell, and any enemy who swats at it is using their action on something other than the party. If the table needs a number for an attack, default to a sting at +2 to hit for 2d4 piercing or so, which keeps it threat-equivalent to its CR.

The wasp does what the handler tells it, within limits. It will not ride in a backpack, it will not stay quiet during a stealth approach, and it will leave to feed if the handler ignores it for an in-game day. If the handler dies, the wasp returns to wild behavior immediately and the party should treat it as an adversary on the next round.

A bonded wasp deserves a name. The player will pick one within five minutes of the first session.

A giant wasp is a CR 1/2 flying nuisance with 22 HP, AC 13, and 50 ft. of fly. The stat block has no actions listed, which means at your table this is a Beast you run with the standard SRD beast logic: it's an aggressive insect defending a nest, and it will buzz a target until either the wasp or the target stops moving. Reach for an unarmed strike or improvise a sting at +2 to hit for a few points of piercing if the players engage. The encounter is the swarm shape, not the per-wasp damage.

Run them in groups of three to six. One wasp is a curiosity. Five wasps converging on the cleric while the rest of the party tries to knock them out of the air with bows is a real five-minute scene. Their fly speed is faster than a humanoid's walk, and Dex 14 keeps them above most low-level martial reach unless someone has a polearm or readies a longbow. Put the nest somewhere the party would reasonably blunder into: a hollow tree across the trail, a shrine eave they want to camp under, the rafters of an abandoned barn.

Wasps are Int 1 and Unaligned. They don't think, they react. Have them home in on whichever PC just hit them or just hit a hivemate. They do not retreat under fire and they do not break off from a target who has fallen prone or unconscious. Once a wasp has decided you are the threat, it stays on you until something stops it. The fight ends when the party kills enough of the swarm to break the rest of the cluster's pattern, or when they retreat far enough from the nest that the wasps disengage and circle back.

Describe the buzz before you describe the wasp. The sound is the warning, and players who hear it twice in a session start checking trees.