The crystal foxes, or vulptex, of Crait are a fascinating example of a familiar species combined with a very unfamiliar design element. At first glance they might seem altogether fantastical and unrealistic, but if we look closely we may find similarities to more familiar animals from our planet that may help us understand this galactic creature’s appearance and behaviour.
Unlike the porgs or thala-sirens of Ahch-To, the terrestrian equivalents of vulptex is quite obvious: foxes, or, more specifically, arctic foxes. With the exception of their otherworldly coats, they are very similar in anatomy, size, and behaviour.
The distinctive coat of an arctic fox is actually only seasonal for the majority of the population, an adaptation to allow them to blend in with the winter snow and ice. During summer, they become brown with a dark grey underside. The vulptex have likely adopted a similar albeit permanent colouring due to the dazzling white of the endless salt flats of Crait.
It is these very salt flats that may explain their incredible crystalline coats. An unlikely but more familiar animal may help us understand how their coats may have evolved: the penguin. Penguins, like other seabirds, spend their lives surrounded by salt water and little to no fresh water. To expel excess salt, penguins have salt glands situated at the front of their skulls, which use osmosis to separate sodium from blood and to expel this excess, in the form of an extremely salty spray, through their nostrils.
It is possible that the crystals of the the vulptex’s coat are in fact salt crystals, made from excess salt excreted through their skin by some mechanism. This means of ridding themselves of excess salt may allow them to cope with the extreme conditions of their planet, such as enabling them to drink saltwater for hydration.
It may also allow them a wider range of prey by avoiding the bio-accumulation of salt. It is likely that most creatures living on Crait will have high levels of sodium due to their surroundings, and without the vulptex’s ability to excrete it, this could pose a serious problem.
Bio-accumulation is when certain elements build up in large quantities in the bodies of animals, most commonly apex predators. These elements, such as heavy metals in our oceans, are consumed in tiny quantities by creatures at the bottom of the food chain, and as they cannot be processed by the body and removed with other waste products, will slowly accumulate in that organism’s body. The quantities present might not affect those creatures, but it will progressively accumulate in their predators and their predators’ predators and so on up the food chain, until the quantity may become great enough to cause significant negative effects.
A further possibility is communication. As heard in the film, their coats make beautiful tinkling noises as they move. The vulptex appear to be at ease in dark cave systems such as the old hangar where the remnants of the Resistance take refuge. The noise produced by their coats could function as a sort of contact call, similar to the wing-beats of mute swans, allowing them to keep track of their pack-mates’ locations in the pitch black of tunnels.
If the crystals of their coat are indeed produced by the excretion of excess salt, then presumably the size of these crystals will increase over the span of each individuals’ life as the mineral accumulates – it could also function as an indicator of the age or state of health of the individual, similar to the way many terrestrian animals use pheromones in scent to encode huge amounts of information.
Although the vulptex’s incredible crystalline coat may seem like nothing more than a pretty design feature to use up some of the film’s special effects budget, when you look past the glitter and sparkles, it’s an unusual but feasible and very useful adaptation to the foxes’ own unusual and harsh home world.