You might be surprised to learn that many animals are actually able to see into the UV part of the EM spectrum. From insects to fish and even certain species of mammal, this trait is quite common.
We humans, on the other hand, appear to either lost it or never had it in the first place. To them, our visual world would look very alien indeed.
Quite why this case is still a matter of debate, but it may well be a compromise for our fairly sophisticated visual acuity. It may also be an adaptation in humans to prevent retinal cancer.
See Also
What animals can see UV light?
So, without further ado, here are some of the most notable animals that can see in UV light. This list is far from exhaustive and is in no particular order.
Butterflies are one member of the animal kingdom that can actually see in ultraviolet. In fact, they are believed to have one of the widest visual ranges of any animal alive today.
Part of the main driver for this ability is their symbiotic relationship with plants. Plants and butterflies have adapted to one another to maximize the chance of pollination and nectar availability for butterflies.
Butterflies also use UV markings that they use to, for example, help find healthy mates. Markings can also make certain species of butterflies appear similar to potential predators while simultaneously allowing members of each species to differentiate between one another.
"The ultraviolet patches on some butterflies are directionally iridescent so that they appear to flicker in flight. This flickering is thought to have an important role in butterfly behavior and communication." - webexhibits.org.
Some higher animals can also see in UV. One example is reindeer.
They have been found to rely on UV light to spot lichens that they can eat. According to an article in New Scientist, this adaptation occurred in response to their migration to Arctic regions over 10,000 years ago.
"The frozen wastes of the Arctic reflect around 90 percent of the UV light that hits them; snow-free land typically reflects only a few percent." - New Scientist.
They can also use light in the UV part of the spectrum to spot UV-absorbent urine from predators during winter.
“Very few mammals see UV light. Rodents do and some species of bat do, but we have no idea why they have developed this capability,” says Glen Jeffery of the University College London.
“This is the first time we have got a real handle on why a mammal uses UV light.”
A species of bird, called European rollers (Coracias garrulus) have been found to also be able to see UV light. While this is apparently quite common in many bird species, scientists were never really sure why before.
One team of researchers in Spain were able to find that for European rollers, one use is to help identify stronger and weaker members of their brood. They are able to check, using UV, to see which ones are healthier and which are weaker.
By studying the young of the species, scientists found that the foreheads of heavier chicks reflected less UV than weaklings. This, it appears, is used to identify at a glance which chicks need more food than others.
Some species of birds have been found to use UV light to find potential mates. When seen under ultraviolet light apparent non-differences between male and female plumage can be quite striking.
"This impacts the study of bird behavior, and our grasp of how birds navigate during migration, classify objects, and interact socially and sexually. For example, some species we see as having identical male and female plumage differ when seen in the ultraviolet range - a difference apparent to the birds themselves." - webexhibits.org.
Some birds have also been found to use UV to spot tell-tale signs of their prey -- like urine or droppings.
Much like butterflies, bees have also evolved symbiotically with certain flowering plants. One example is the flowers of Black-eyed Susans.
This plant's petals appear yellow to use lowly-humans, but to bees the look very different indeed. Under UV light, the flower's petals form a bulls-eye like design that is very attractive to certain pollinating bees.
"The bright colors of flowers (and patterns in the reflected UV, or ultraviolet, energy) attract bees to flowers and even to specific areas on the flowers. The bees like the flowers as a source of sweet nectar, which they process into honey for their food. The flowers like to attract the bees so that pollen from their flowers can attach itself to the bees for a free ride to another flower." - rit-mcsl.org.
There is a growing body of evidence that some fish species, like the Sockeye salmon (Oncorhynchus nerka), can also see in UV. According to some research, they may use UV to find food.
What is odd though is that the UV-receptors in their eyes appear and then disappear at certain times in their lifecycle. It is believed that this coincides with the times of prominent feeding on zooplankton and smaller fish who likely show up better under UV light in youth.
Dogs and cats may also be able to see in the UV part of the EM spectrum. While both can show some very odd behavior at times, sparking myth that cats may be able to see the dead, it could have a less supernatural explanation.
In fact, as we have seen, there are quite a few animals who have the same ability. Humans, for some reason, have lost, or never had it.
As they can actually see things we can't, it is natural for humans to find some of their behavior a little odd.
And lastly, but by no means least, is the humble hedgehog. These elusive nocturnal mammals have also been shown to be able to see using UV.
"A study by Ronald Douglas and Glen Jeffrey published in the Proceedings of the Royal Society B in 2014 found that hedgehog lenses transmitted a significant amount of UVA light, suggesting they may have a vision in the UV spectrum despite lacking a specific UV pigment." - wildlifeonline.me.uk.
It is believed that it helps them navigate at night, find their food, and spot potential predators.
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