What lies awake at night? (Image: Michael Nichols/NGS)
Read more: “The night: The nocturnal journey of body and mind“
DOES a rustling in the deep dark of night send a shiver down your spine? The fear may be justified. Many of the creatures of the shadows, only glimpsed as flitting shapes, are ones to avoid. From the dangerous to the curious to the downright strange, the night-time is teeming with life.
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In our 24/7, artificially lit world, humans are active around the clock. But don’t be fooled: the night is an alien place to us. Our evolutionarily closest relatives, the chimps and bonobos, are diurnal – they operate strictly during daylight hours, bedding down at dusk. And a look at the habits of all extant primates indicates that our forebears have been adapted to daylight living for more than 50 million years.
Nevertheless, night-time was the right time for our earliest ancestors. Mammals evolved some 200 million years ago, when dinosaurs were in their prime. Being able to generate their own heat, these small rodent-like creatures did not need to bask in the sun to raise their body temperature and activity levels, so nocturnal life was an option – and an appealing one. By occupying the darkness, they could with diurnal dinosaurs.
That heritage explains key features of mammals today, especially their keen senses of touch, smell and hearing, and relatively poor vision. Indeed, many rodents remain nocturnal, from pet hamsters to the extravagantly named octodon, which is actually a nondescript mouse-like creature. Then of course there are rats, scratching around in the putrid remains of civilisation, infesting our sewers, gorging on our leftovers, spreading diseases.
The extinction of the non-avian dinosaurs, around 65 million years ago, allowed mammals to evolve into daytime niches and get larger. Nevertheless, the majority of carnivorous mammals are still nocturnal or crepuscular, stalking at dusk and dawn, and in the hours between. Two groups are particularly fearsome: the canids – including coyotes, hyenas and that classic night-fright, the howling wolf – and the big cats. In fact, the threat posed by leopards, jaguars and the like may help explain why we have evolved to overreact to any suspicious rustling in the dark.
Less familiar nocturnal mammals also abound. Take the honey badger – not as sweet as its name suggests. Found across Africa and Asia, its caution-to-the-wind attitude to predation earned it a place in the book of Guinness World Records as “most fearless animal”. While its reputation for going straight for the genitals has little basis in fact, it will happily take on venomous bees and snakes. Even faced with a vicious cobra, it attacks head-on before munching down the body.
See more nocturnal beasts in our gallery: “The night: The creatures to avoid in the dark“
Mammals are not the only undesirables out after dark. Long before our lineage evolved, insects inhabited the night. They are the smorgasbord that sustains many nocturnal animals, including the first mammals. If the half-perceived flit of a bat doesn’t alarm you, what about the piercing whine of the mosquito that could be its next meal – or make a meal of you? Whatever your personal bugbear, you have to admire , discriminating not only shape but colour, and even orienting themselves using faint celestial cues.
There is another survival advantage to being active at night: in tropical and arid regions it allows animals to avoid overheating and water loss. Some of the most fearsome denizens of the night are desert dwellers. They include rattlesnakes, which detect prospective prey using infrared heat sensors, and the Gila monster, a huge venomous lizard that lives in the deserts of Mexico and the US.
Then there are scorpions. Armed with pincers and stingers, even the small ones pack a punch. But they also posses one of the most beautiful nocturnal adaptations, a cuticle that absorbs ultraviolet light and emits a green glow. light and one idea is that scorpions use their fluorescence to spot one another, distinguishing mates from competitors, which they will often eat. Alternatively, the glow might be to attract another food source, moths. Or perhaps it is a warning to the scorpion itself. Too much glow signals the moonlight is strong enough to make it visible to predators, such as owls, other scorpions – and honey badgers. Two of a scorpion’s eight eyes are well positioned to keep tabs on its own body. And experiments reveal it will .
Another good reason to inhabit the night is to avoid day-prowling predators. Indeed, it was once thought to explain the nocturnal origins of mammals. But this idea may be based on a misconception. There is now convincing evidence that many dinosaurs – including the velociraptor – preyed by night as well as by day. If today’s nocturnal inhabitants seem fearsome, just be thankful that dinosaurs are no longer a part of the night life.
This article appeared in print under the headline “Things that go bump…”
