The stilt-legged spider-like automatons had large balloon-like heads atop their thin stalk bodies, armed with laser turrets. They were named after the eight-eyed, gasbag-headed vine walkers native to Skako. They were equipped with three laser turrets as standard, one on each side, below each photoreceptor. A certain variant was filled with a gaseous virus that would be released upon the droid's destruction, which was highly effective against organic enemy troops. The virus variants were nicknamed "virus droids".
Their rotating multi-jointed assemblies allowed them to change facing almost instantly and they could fire from extended ranges, though they were vulnerable in close-quarters fighting. It was almost impossible to approach such droids, as all sides conceivably faced the front.
Certain battlefield demands led to the creation of a larger model: the Tri-Droid. The Techno Union decided to reduce costs by scaling up the size of previous models. Chain-fed ordnance launchers replaced the laser cannons of its predecessors, with the reserves of ammunition stored within the hollows of its bulbous head, although some models did retain laser cannons as seen in the Battle of Christophsis. One rocket fired from a single behemoth was powerful enough to annihilate an UT-AT if aimed correctly, as seen in the Battle of Mygeeto.
During the Battle of Coruscant, a group of octuptarra tri-droids used their laser beam cannons against Jedi MastersMace Windu and Yoda. The beams could be maintained, similar to the OG-9 homing spider droid's turret, so the Jedi were able to destroy several tri-droids with one beam by deflecting it with their lightsabers.
When the battle was over, the remains of the droids fell into the Coruscant underlevels, where strains of the virus leaked out and caused an unfortunate outbreak of moulting in the city's numerous avian species.
There seem to be a contradiction about the height of the up-scaled Tri-Droid version of Octuptarra droid. The Databank gives the height of the tri-droid as 3.7 meters, which is only slightly more than the height of the octuptarra droid. However, all visual sources portray it as many times larger than a Human, and even the same Databank entry describes it as "gigantic" compared to the 3.6 meter octuptarra droid. While it is safe to assume that "3.7 meters" height is an error, the exact height of the up-scaled variant remains unknown.