Spore Mine
A Spore Mine (Boletus minoris) is a living, floating Tyrannic creation which will explode if any non-Tyranid creatures gets too close to it. They are created by Biovores and Sporocysts, who gestated the mines deep into their bodies, who them launch the spore with a powerful muscular spasm from the long tube on their bodies... and if you are feeling uncomfortable reading this trust me you should.
The mines float through a gas bladder shake and they slowly drift alone, minding their own business until any non-Tyranid without a brain gets too close. Of course this means any random rabbit could set these things off but then what do you expect from the intelligence of cosmic bugs? They have been known to drift for months or even years before they are set off. They are said to possess a low animal intelligence despite not having a head and can feel heat and vibrations through feelers on their bodies. They are full of all sorts of delightful poisons and toxins that would make a Slaanesh worshipper swoon with delight and capturing them as a delicacy for a Keeper of Secrets is said to bring high rewards.
They come in three fun varieties: Poison Spore Mines (full of poison duh); Frag Spore Mines (which have lots of sharp shards in them and explode like a grenade, don't fix what ain't broke right?); and Bio-Acid Spore Mines (which spray stinky acid everywhere and well, you can guess what happens next). There's also something of an unofficial fourth variety called the Mucolid Spore. While largely similar in appearance, these spores are unique not in what they explode into (Mostly gases), but by the fact that they can also use these gases to fly higher than any other spore and end up on the flight path of an unfortunate Valkyrie/Heldrake/Dakkajet, exploding in front of the flyer.