Squig Catapult
In the grimdarkness of the 41st millennium, the humble catapult still somehow found some use in a world filled with Titans and Tanks. Possibly still trying to keep Warhammer Fantasy alive through 40k, the Orks Grots created the Squig Catapult or Katapult which hurls a pot of Squigs (Usually coming from the Buzzer Squig or Buzzing Squig variety).
They are constructed from bits of scrap metal and wreckage of destroyed enemy or Ork vehicles and form large girder-like structures with perforations to reduce the overall weight. Each section is bolted together before battle but can be carried by gretchin runts between battles. The firing mechanisms of the Catapult should be quite self explanatory, but what makes this Catapult unique is its ammunition.
As said before, the Catapult throws a pot of Buzzer/Buzzing Squigs, a special kind of Squigs which are essentially flying piranhas, and that goes hungry and angry very quickly and can strip a man-sized target into bones within mere minutes. And although woefully inaccurate even by Ork Standards, the Squigs are mobile enough to find their nearest target, compensating for that flaw. This means that the Orks are the only faction that is capable of out-NOMMING the Tyranids in their own game and it is often advised to look at the face of a 'Nid player as his entire Gaunt army is reduced to giblets. Heck even tank crews and fucking Dreadnoughts aren't safe as the Squigs are small enough (They are roughly the size of a mosquito) to fit through any cracks or holes (in the case of the Dreadnought, the entire eye slit) before eating the crew alive.
Just like most Ork tek, there is a high probability that something will go wrong. When the catapult fails, it is usually quite spectacular, either it manages to destroy itself as the strain of operating gets too much, or a minor fault prevents it from firing at all. On occasion a gretchin is loaded by mistake, sending it to its death as well as some of the enemies in its path.