Somewhere over the rainbow, just past our visible spectrum lies the hidden world of ultra violet light. UV light has very short wavelengths between 10nm – 400nm. A massive range of insects, birds, fish, reptiles, plants and animals have evolved to use UV light to find meals, attract mates and communicate safely out of sight from predators (and us!). But now, kitted out with UV goggles and high definition cameras, we’re getting a closer look at the action.
Insects like the Sara Longwing butterfly are able to see wavelengths of light as short as 310nm. This ‘sixth sense’ allows pollinating insects to spot hidden UV markings on flowers. Take the aptly named plant Black-eyed Susan, which has UV absorbing pigments called flavonoids in the centre of its flowers. Although invisible to us, insects find these UV pigments totally irresistible. They act like dark bull’s eye targets, guiding towards delicious nectar food. And of course, plants also get something out of this meal deal: pollination!
Rafflesia plants are slightly more sinister and use UV markings to coax insects into their gaping mouth-like flowers. Once the insects land, the flower’s slippery surface causes the insects to fall and drown in the plant’s digestive juices. And equally deceptively, some crab spiders use UV decorations to trick honeybees into their deadly webs.
Scorpions are slightly more conspicuous… they glow in the dark! Scorpions naturally like hideaway from nighttime predators by keeping in the shade. Even the faint glow of the moon and stars could give their game away. Spookily, scorpions’ bodies are coated in a pigment, which converts UV light into a bright cyan-green florescence. Researchers now think this glow is picked up by the scorpion’s own sensitive eyes, raising the alarm and allowing the scorpion to run for shade before they become bird food.
In the underwater world of the coral reef, fish are also raving about UV. The Ambon damselfish uses UV patterns to recognise the faces of invading fish, which compete for food and mates. Their bigger predator, the coral trout lacks UV vision, keeping the damselfish’s golden camouflage hidden from view. But other fish find UV markings sexier and like the northern swordtail fish, who use them to attract the ladies.
Back on land, birds find UV pretty fit too. The robin’s red breast and the blue tit’s crest appear as bright UV beacons to females and definitely earn a few extra man points. Common Kestrals even use UV vision to pick up the trails of their prey, which feed on berries rich in UV pigments.
Finally, most large mammals (including us) have sensitive retinas, which are protected by UV proof corneas and lenses. But bizarrely, last year scientist Glen Jeffery and his team at UCL made a pretty ‘cool’ discovery: Reindeer can see UV! Reindeer feed off lichen and are hunted by wolves, which both absorb UV light, appearing dark and easily visible against the snowy white background.
Current research like this is shedding new light on a hidden UV world and with so much action going on right under our noses, there’s definitely more than meets the eye!