Where Big Creepy-Crawlies meets mecha. A subset of Real Robot, with a decidedly non-humanoid appearance. These are often used by sci-fi series that want to use giant robots, but feel that humanoid shapes won't fit the setting. Even if the setting doesn't use giant robots, and sometimes even if it does, smaller Spider Tanks may be found as robotic drones. In series that use giant humanoid robots as well as spider tanks, you can bet that the humanoid robots will often be more agile than their multi-legged counterparts, despite the fact that the opposite logically would be true.

The form has a few advantages over the human shape:

• The hull can be lower to the ground and thus less of a target;
• Your classic Spider Tank spreads its legs out more, making the vehicle more stable overall and allows it to traverse terrain that would give wheeled vehicles considerable trouble.
• Increased points of contact with the ground also increase stability — the human shape is a lot more precariously balanced than it seems, and bipedal robots in real life tend to have serious balance issues. Giving a machine multiple legs helps it keep its footing.

These help it cheat that pesky Square-Cube Law that gives giant humanoids considerable engineering problems. Of course many creators then go ahead and give it feet that taper to a point in order to make it look more like a real arthropod, which ruins any overall improvement in the ground-pressure department. You can't escape the Rule of Cool, it seems.

While wheels are faster and more efficient and tracks are best on a soft ground (it's hard to beat one big support area), spider legs can navigate extremely rough terrains and are more reliable because the vehicle can stand or even walk after losing a leg or two. Since "extremely rough terrains" include rubble blasted all over streets or hedgehogs made of rails, and "losing a leg" includes little gifts from artillery, you see why an excavator isn't the only potential application. In fiction this means the spider design is most attractive for settings supposed to be gritty and realistic.

Depending on the size of the Spider Tank, it may or may not have wheels on its feet. Caterpillar tracks are also common. If the Spider Tank is under 4 meters (roughly 12.5 feet) tall you can expect it to have wheels or tracks on its feet; if larger, you can expect it won't. It will probably have pointy feet instead. Despite the name, Spider Tanks rarely have eight legs. Four is the most common, and some have six. It's usually guaranteed that they'll have an even number of legs, though.

Please note, Spider Tanks are not tanks designed to look like spiders; they are simply tanks that walk like spiders (or scorpions). If you encounter a giant robot shaped like an insect or arachnoid it's more likely that they are a Ro Beast and not a true Spider Tank. In video games some Real Robot humanoid mechas occasionally have four or more legs, but still have an upper body and arms. They are also not spider tanks, as they do not fulfil the tank requirement. It's also not an arachnid version of the Snake Pit or Shark Pool.

A similar (and broader) concept is Tripods. See also Giant Spider and Giant Enemy Crab for their autonomous organic counterparts. Sub-Trope of Walking Tank and, depending on the type of Spider Tank, Animal Mecha or Starfish Robots. Contrast Tank-Tread Mecha (for machines with the lower body of a tank). The more autonomous versions may overlap with Mechanical Insects.

Examples: