Slaver wasps are biomechanical mind-control devices created by the Other, as confirmed by Lady Vrin, who also that they're called "Shk-mah" in the language of the Geisterdamen. They come sealed in (or are produced by) large devices known as hive engines, and someone who has been infected by a wasp is called a revenant. These revenants, as well as the wasps themselves, are programmed to recognize and obey the Other's voice.
Though there are no known instances of a revenant ever being cured, "" The majority of those infected by the wasps remain outwardly normal, just controllable - and possibly even unaware of their condition.
Tactics EditOnce a hive engine is activated, a number of "warrior" wasps swarm out to secure a perimeter while the "queen", which is part of the engine, generates the smaller wasps that carry out the actual infection. Anyone caught within this perimeter is herded toward the engine and immobilized.
When the swarm is complete, it is released in one burst to seek out all potential hosts.
In terms of physical constitution, it seems the human-sized warriors are roughly comparable to an armored human warrior, while the infection wasps are roughly comparable to the insect after which they are named, and are vulnerable to proportionate physical insults, despite the numinous fear they may inspire. (As opposed to ghouls that appear in other stories such as vampires, golems, carbosilicate amorphs, etc.) Along the same lines, although termed an "infection", there is no suggestion that the infection can be communicated directly from a revenant or that the wasps reproduce other than within a hive engine.Furthermore, at least one sort of general-purpose poison gas used on Castle Wulfenbach was shown to deactivate the wasps, contrary to what might be expected for a purely mechanical device.
Being mindless servants of the Other, the wasps will evidently obey her command voice (or sufficiently similar voice) regardless of the actual source.
A slaver wasp (or the pathogen which it carries) evidently emits a characteristic odor that can be detected by wasp eaters, which are constructs designed to hunt wasps, drawing on the natural characteristics of weasels, which frequently hunt by scent and are occasionally insectivorous. Likewise, by all accounts, Jägermonsters have a taste for "bogs" which extends to slaver wasps.
Although there's no cure for infection, by the end of Act 1 there is an inoculation draught.