Spider Splicer
Spider slicers are the assassins of the bunch. They're the most agile splicers that you'll come across, with the ability to sink their meathooks into the ceiling and crawl along it; you'll hear them jabbering as they do so, as well as hear their distinctive clanking sound, and you'll also see material falling from the ceiling, so this isn't exactly a stealth move, but it can be a surprise. They'll usually prefer to drop to the ground and slice at you before flipping away, but they can also throw their blades at you from a distance, whether they're on the ground or on the ceiling.
In general, spiders are pretty tough to kill, mostly due to the unpredictable way they move. After you research them a bit, though, they get a little easier. Napalm puts them down pretty quickly, and wrench attacks work reasonably well if you use the correct tonics.