And it's actually multiple entities, with their collision shapes not exactly obvious from visuals. You can't really kill them with manual fire weapons (like AM Afflictor), and most weapons that will reliably hit them on autofire don't have enough dps (and won't prioritize them with other targets around). Plus, if killed near fabricator, reclamation will be pretty much instant.
So really, trying to kill reclaim swarms is a fake option at least most of the time. Maybe you could make it work, if you designed your whole fleet for that purpose alone (but then it may end up bad at actually killing threat ships...).
I've been tinkering with a hexa-IRAL Executor for this purpose (in addition to bursting down exposed hull from afar), as well as swapping out escort Enforcers for some IRAL-equipped Eagles. It's not going great. The autolance, especially six of them, has got the damage to zap Reclamation Swarms quickly, and the range to do so even when they're coming off of a ship that's a good distance away. But when left to their own devices the Eagles just kind of fart around, it's a coin toss whether the IRAL is going to target a Reclamation Swarm or an Attack Swarm, assuming it's not already busy shooting a ship. When I'm flying the Executor, targeting manually and using HEF, I can rapidly pick swarms off. Even can clean up the half-dozen that flew off a dead Line Unit, which I hadn't even thought possible. But the battle of attrition still swings against me every time. I fight my way to the Fabricator after killing as many Reclamation Swarms as I feasibly could, it still has something like 50%+ CR, the noose closes, Overseers sitting 2000+ units away flick freshly-built Assault Units at me like so many boogers, the end. It doesn't feel like I'm on to anything trying to deny swarms.
The only Reclamation Swarms I was reliably denying before trying the laser pointer strat were ones that flew off of dead Skirmish units that were behind my fleet, and ones that flew off Assault units that died nosediving my fleet. Because the Overseer and Line units seem to prefer to keep a good distance from my ships, by the time they die the swarms that will spawn from them are usually out of range of most weapons. My ships will tag them with a beam of some sort or chuck a Mauler burst at them, and then they're home free. What makes matters worse is that while swarms are flying off of a dead unit, the hulk still blocks incoming fire, until the last swarm is away. So if your ship, the dead ship, and the Fabricator are more or less aligned in syzygy, the Reclamation Swarms will get a head start on top of their head start. Line Units are notorious for this in my experience due to their overall bulk and the number of swarms they generate.
What if a hulk decomposing into a Reclamation Swarm just exploded into its components all at once, instead of peeling away bit by bit? I do love the visuals of the gradual disintegration, but the effect it has on gameplay is a negative. Or what if Reclamation Swarms just had reduced health, since the window of opportunity to attack them is so slim?