I checked it by myself, since some time ago raids was my favourite hunting place and I realised, that I don't know the answer ;)
As Xarkost said Unstable Tunnels are active only during a wildlife creatures raid, which takes place on the west side of Glooth Factory middle level.
First of all Unstable Tunnels have big area attack, which looks like poison, but deals energy damage. Even thought hits made by one tunnel may be considered as weak one, then it maybe dangerous if player is trapped with 8 monsters and few tunnels next to him.
As it is already said: Unstable Tunnels are able to summon up to 4 wildlife creatures (the most common are Drillworms, but you can also meet Glooth Anemone and Behemoths). Why? I guess that it was designed to make fake crowd on the spawn. It may be problematic to run with a lot of monsters AND try to not trap with those useless ones - because monsters summoned by Tunnels gives no corpses, and no loot at all. When you kill them - they simply puff.
Monsters (summons) won't attack you, untill you stand directly next to the Unstable Tunnel. On the picture below you can see, that I'm standing next to the summoned Behemoth, and nothing. He doesn't attack me and... simply doesn't see me. I can even attack him, but it won't trigger any activity until I stand 1 SQM nexy to the Unstable Tunnel.