Starship Troopers movies & novel
As a large Arachnid used against Mobile Infantry, the Tanker Bugs resemble a giant beetle and play the role of tanks/armors of the Arachnid forces.
The Tanker Bugs are generally black in color and are nearly as large as Plasma Bugs. They have evolved the ability to spray a stream of flammable, corrosive liquid from its head.
The Tanker ejected fuel from a nozzle-like spout in the top of the head. With each Arachnid serving a specific military role, the Tanker Bug functions as a form of armor support. Their thick exoskeleton provides them with excellent protection, though not immunity, from rifle rounds, allowing them to take quite a beating before being killed. They are however vulnerable to explosives, such as grenades thrown by the human troopers, particularly in weakened areas of their shell.
Tanker Bugs were used by the Arachnids during the Klendathu System Campaign when the Federation tried to capture Arachnid planets in the system one at a time. During this campaign, several Tanker Bugs were seen on Planet P and Tango Urilla where they commonly attacked Mobile Infantry forces by tunneling underneath them and coming up behind the Mobile Infantry lines.
Roughnecks: Starship Troopers Chronicles
The Tanker Bugs are the size of houses and breathe fire as their main offensive weapon. Although they don’t move quickly, their ability to tunnel underground allows them to pop up unexpectedly in the middle of a battle. Their armored exoskeleton makes them near-impervious to everything except high explosives such as mini-nukes and plasma rockets.