| 1 | A secret Australian killer |
Every Australian is familiar with tiger snakes or eastern browns, but there’s also a less famous venomous snake out there, which has killed 1 person since 1960 and has a venom strongly targeting muscle tissue. This is the small-eyed snake (Cryptophis nigrescens), which measures 40-100cm, and does have some small, beady black eyes.
This venomous snake is one of the least commonly encountered by ordinary Australians, mainly because of its nocturnal lifestyle. Small-eyed snakes exclusively occupy Australia’s east coast, skipping the barren central outback, and pushing as far north as Cairns. They appear in various habitats, but cannot survive in bone dry environments. Forests are acceptable, as are fields and shrubland. Small-eyed snakes don’t care whether a location has dense trees, sparse trees, or no trees. The main conditions they require are plentiful moisture, and an abundance of rocks to shelter beneath.
The best rocks to find small-eyed snakes under are those in grass or directly next to leaf litter, as these are magnets for their skink lizard prey. Small-eyed snakes also lurk beneath fallen timber and loose bark, but rocks are their favourite. Unlike eastern browns, it’s rare to find this venomous snake slithering around towns and cities – tracking one down requires an adventure.
| 2 | Destroys all muscle tissue |
The small-eyed snake doesn’t have extraordinarily deadly venom, but possesses one power above all else: the destruction of muscle tissue. The venom is strongly myotoxic, causing muscle weakness and heart damage.
One symptom is myoglobia, a flood of myoglobin in urine as a byproduct of muscle tissue destruction. Initial symptoms of small-eyed snake evenomation include hypotension and an elevated heartbeat, but while these fade within hours, the muscle damage can take 3-4 days to fully reveal itself, and progress for weeks afterwards. This is an especially slow-acting venom.
The only confirmed small-eyed snake fatality happened in 1965, to an expert snake handler. He arrived in hospital 3 days post bite, complaining of a stiff neck and jaw. He was discharged, but later readmitted with lower limb pain. The victim now suffered from jaundice and dark brown urine (AKA the myglobia). Doctors performed a tracheostomy and placed him on artificial ventilation, but the man died on May 19th, a full 10 days after being bitten. An autopsy the previous day showed that large areas of his muscles were necrotic.
| 3 | No antivenom exists |
Small-eyed snakes have the worrying honour of having no specific antivenom. If you crawl to a hospital, there’s no dedicated cure waiting for you. However, a 2000 study concluded that tiger snake antivenom works extremely well, since the two species have a large overlap in toxin types. This study gave us another detailed bite report…
The victim was kneeling in long grass in his garden, when he felt a pricking sensation in his leg. He assumed he had leant on a sharp stick and brushed the incident aside, but soon experienced severe abdominal and muscle pain. His heart rate reached 114 beats per minute, and his body temperature reach 38.5C. The main symptom doctors noticed on arrival was the muscle abnormalities. All the victim’s limbs were in maximum flexion, and his abdominal muscles were tensed involuntarily.
Tests revealed massively elevated creatine kinase levels, a biomarker of muscle tissue destruction, which is also used to diagnose muscular dystrophy patients. The venom was spreading, and time was short to prevent a repeat of 1965. With no dedicated antivenom, the scientists injected tiger snake antivenom instead, triggering a precipitous fall in creatine kinase within just 30 minutes. The man was sent home.
| 4 | Smaller eyes exist |
Fortunately, the 1965 death is still the only one on record. Small-eyed snakes are shy and non-aggressive. They’ll strike if cornered, but in a haphazard style rather than ruthlessly precise. A study found that they default to fleeing, compared to the broad-headed snake (also Australian), which was more aggressive. Additionally, small-eyed snakes stayed nimble and alert in a wider range of temperatures, while broad-headed snakes became sluggish at lower ones.
Likewise, the venom was once estimated to be just 21% as toxic as an Indian cobra’s. The LD50 score is 2.67mg, falling well short of an eastern brown snake (0.05mg), and failing to match a red-bellied black snake (2.4mg).
Even Cryptophis nigrescens’ eyes aren’t special. While small, the brown-headed snake (Furina tristris) of Queensland has even tinier eyes, as does the golden-crowned snake (Cacophis squamulosus) of Australian forests. One eye-catching stat is that a small-eyed snake’s fang puncture marks are separated by precisely 6mm.
| 5 | Diet: a skink obsessive |
The small-eyed snake completely ignores mammals. They’re not only an exclusive reptile hunter, but get most of their calories from the skink subgroup. They eat no geckos, whereas their neighbour the broad-headed snake gets over 50% of its calories from one species, the velvet gecko. The two have separated into cleanly divided niches, to avoid competition with each other.
One study examined the stomach contents of C nigrescens (including 560 snakes) and its close relative, the northern small-eyed snake (40). Across the two species, 89% of the prey discovered were skinks, and 5% were snakes. The remainder included agamid lizards, legless lizards, and lizard eggs. There wasn’t a single frog, insect or gecko.
Small-eyed snakes have never been witnessed eating frogs; the closest observation was two snakes which held frogs in their mouths. They probably made a hasty lunge and tossed them aside after being disgusted with secretions in their slimy amphibian skin. The scientists concluded that “The food habits of Cryptophis appear to be less diverse than has previously been suggested“
| 6 | Uses scent rather than vision |
Confirmed prey of the small-eyed snake include common garden skinks (Lampropholis guichenoti), common scaly foots, and the neighbouring blackish blind snake. Instead of an immobile ambush predator, the small-eyed snake is an active forager, and they always hunt at night. It’s a well oiled machine, as small-eyed snakes always wake up at dusk, just as the local skinks are falling asleep. The small-eyed snake then seeks them out in their dens, such as between rock crevices or grass tufts. Studies have found that discovered skinks hardly ever evade capture – their prospects of survival depend on choosing the best shelter in the first place.
Another study gathered yellow-faced whipsnakes, small-eyed snakes and death adders. Each was placed in front of a common garden skink. All showed interest, but the small-eyed snake flecked its tongue by far the most. Being nocturnal, this snake is particularly reliant on smell and chemosensing, which may be why its eyes have become so beady.
| 7 | Your handy ID guide |
The small-eyed snake combines glossy black scales with a far lighter belly. This belly varies by location, from a creamy yellow in the south, to pale pink in the north. Small-eyed snakes have particularly shiny scales, which reflect a camera flash and are smooth to touch. They have virtually no patterns, but up close, each scale has a slight pale outline. Their scales are honeycomb shaped.
From above, a small-eyed snake’s head is only slightly larger than its neck. The head is even blacker than the rest of its body, and unlike the body, the head has a small handful of much larger scales, like armoured plates.
Cryptophis nigrescens is commonly confused with the red-bellied black snake. They average at 50cm, smaller than the red-belly’s 1.25 metres, but small-eyed snakes can occasionally break far beyond this and reach 1.5 metres. The belly is the clear difference. In red-bellied black snakes, the contrast between red and black is far more vivid, while with small-eyed snakes, they blend together more. The red belly is rarely as intense with the small-eyed snake.
| 8 | Sniffs out its fellow snakes |
Small-eyed snakes have been spotted in groups of 20 in the wild. They’re more socially complex than once believed, as a 2012 study found that they’re more likely to take shelter in areas covered with their own species’ scent, even if no actual snakes were there.
Females were attracted to pheromones and scent particles of either sex, while males were interested mainly in female scents (not surprisingly). Males were particularly attracted to scents from larger females, possibly hoping that they’d come back. This makes sense, as in the snake kingdom, larger females nearly always lay more eggs.
It’s possible that these small-eyed snakes were simply seeking mates. But there may be a more cunning explanation; that small-eyed snakes were using old scent accumulations as evidence that a particular grass tuft or rock crevice had better survival prospects. The common keelback does something similar, as one study found that they prefer to lay eggs in dens where old shells were scattered around, using these as evidence of hatching success. Snakes are intelligent in hidden ways.
| 9 | Wildfire weakness |
Small-eyed snakes aren’t close to endangered, with a healthy range across Australia’s east coast. But they have one weakness: wildfires. A study compared them to the broad-headed snake, a severely endangered snake, which is limited to rocky outcroppings in a handful of national parks. It found that for all their weaknesses, broad-headed snakes were barely affected when wildfires tore through an area, probably because they could vanish into dark crevices.
Meanwhile, the local population of small-eyed snakes plummeted by 48%. Annual survival of the local small-eyed snakes decreased by 38%. Scientists didn’t know the exact reason, but linked it to their active foraging methods. The snakes continued to prowl around searching for skinks, but as the wildfire had burnt off tree and vegetation cover, they were now far more vulnerable to bird predators.
Broad-headed snakes are an ambush predator instead, which stay still for days, and are therefore less exposed. The study took place in Morton National Park, 110 miles from Sydney, which was badly affected by wildfires in 2001-2002.
| 10 | Secret facts |
As well as longer, male small-eyed snakes are far more adventurous than females. A study found that while females were recaptured 35 metres away from their original spot on average, males were recaptured 99 metres away.
The more time elapsed, the further away the males became. 6 females were recaptured under the very same rock as originally. With small-eyed snakes, it’s males that disperse the populations and genes, which ultimately allowed them to conquer the whole east coast of Australia.
Cryptophis is a family of 5 species, all in Australia and New Guinea. Another is Cryptophis pallidiceps, AKA the northern small-eyed snake. This version is equally shy, the same length (50cm), and its body is equally shiny and glossy. Its range doesn’t overlap with its eastern cousin, as it lives in the Kimberley region of Western Australia and upper Northern Territory instead. It looks similar, but the lighter belly scales spread further up on each side, particularly its head, which has a beige underside. In this version, males and females are equal length.