These huge beasts of burden made their debut in the origin Star Wars, and have popped up from time to time ever since.
It is clearly baking hot and there is not a snowflake in sight
They look an awful lot like woolly mammoths, an extinct species that once roamed much of the Northern Hemisphere. Like the mammoths, banthas have long tusks and hairy, shaggy coats – although they do lack trunks.
This is actually rather odd. Woolly mammoths thrived during the recent ice ages, when huge sheets of ice expanded from the Arctic and covered North America and northern Europe. The mammoths' huge size and thick coats helped them to stay warm in the frigid climate.
In contrast, banthas live on the desert planet of Tatooine. We never see an onscreen thermometer but it is clearly baking hot and there is not a snowflake in sight. The banthas ought to overheat.
We can only conclude that they were imported from somewhere else, perhaps the ice world of Hoth, or else someone has selectively bred them for their fur.
Speaking of the ice world of Hoth, its native tauntauns were used as beasts of burden by the Rebellion while it was based there in The Empire Strikes Back.
They have thick fur, of a dirty white colour – which makes sense given the snowy landscape they live in. But they seem rather unsuited to being ridden by humans.
So far we have no evidence that any asteroids in the solar system are inhabited by huge worms
Almost all the animals humans ride are four-legged, the most obvious example being horses. But tauntauns are bipedal, holding their arms in front of them in the manner of a predatory dinosaur like Tyrannosaurus rex.
This means all their weight is supported by their hind legs. You would think that a tauntaun would buckle under the additional weight of a parka-clad Luke Skywalker.
But not necessarily. There is one bipedal animal that humans can and do ride: ostriches. If they can handle it, presumably tauntauns can too.
Wait, what? These are never named onscreen, but they were memorable nonetheless. In The Empire Strikes Back, Han Solo hides the Millennium Falcon in a tunnel in an asteroid – only to discover that the tunnel is home to a gigantic worm-like creature and he has parked his ship on its tongue. This beast was subsequently named as an Exogorth.
So far we have no evidence that any asteroids in the solar system are inhabited by huge worms, and it does seem rather unlikely. But the various elements of the Exogorth, on their own, have a basis in reality.
For starters there are plenty of long animals that spend most of their time in burrows. Here is a spotted moray eel living in a pipe.
A more challenging question is: what might an Exogorth eat? The science fiction writer Arthur C. Clarke argued that the animal was implausible, because Princess Leia would not have made for much of a meal, and presumably not many prey animals wander past. But that assumes it eats flesh.
Could a slug ever grow as large as Jabba?
Many single-celled organisms can derive energy from ground-up rocks: millions of such microbes are living in lakes underneath the Antarctic ice sheet.
Such microbes can support larger, more complex organisms. We now know that worms can live in solid rock several kilometres underground, where they feed off films of bacteria.
Admittedly, these worms are only a few millimetres long, whereas the Exogorth was hundreds of metres. But still.
Jabba the Hutt
This criminal mastermind is essentially a gigantic slug, with arms.
Setting aside the question of whether a slug could ever evolve sufficient intelligence to run a criminal empire with enough ready cash to hire a court jester, could a slug ever grow as large as Jabba?
The giant African land snail can sometimes reach 30cm
Slugs and snails are molluscs, meaning they belong to the same group as clams, oysters and octopuses.
The largest molluscs are probably colossal squid, which can reach 12m long, but they are not a good guide. Most of the length is made up of trailing tentacles, and they can only grow so long because they live underwater.
Slugs and snails – technically known as "gastropods" – have rather more compact bodies, and that limits their size. The California black sea hare is one of the very biggest, reaching 0.99m long and weighing 14kg. But again, it is a marine species and that means it can grow unusually large.
If we confine ourselves to land, the giant African land snail can sometimes reach 30cm. But some of its size and bulk is made up of its large shell, and Jabba doesn't seem to have a shell.
Among shell-less gastropods, the black keelback slug may well be the largest. It can grow to 20cm long.
Somehow a crime lord smaller than a laptop computer doesn't seem quite so intimidating.
Jabba the Hutt is evidently keen on florid methods of execution. In Return of the Jedi, he tries to have our heroes hurled into the Pit of Carkoon, which houses a monster called the Sarlacc. "In his belly," Jabba informs them via an unwilling translator, "you will find a new definition of pain and suffering as you are slowly digested over a thousand years."
We never see the Sarlacc's entire body, because it has buried itself in the sand. It lies at the bottom of a sand pit with steeply-sloping sides, so anyone who falls in finds themselves inexorably sliding to the bottom.
This is reminiscent of one of the greatest insect predators: antlions.
The larvae of these insects prey on ants, and to do so they build traps. They dig little pits in the sand, a few centimetres deep.
The slope of the finished pit will be at a very particular angle, known as the critical angle of repose. It is as steep as it can possibly be without collapsing on its own, and the slightest disturbance will send sand tumbling to the bottom.
This means that any animal wandering into the pit will find itself sliding into the depths – where the antlion is waiting, its huge jaws agape.