| 1 | Thailand’s deadliest snake |
In Thailand, there’s one snake which locals fear above all else. It can lurk under tables, porches, fridges, beds, and baskets of melons outside markets. Most Thai people have a horror story involving a relative or friend, and bizarre legends such as its mate hunting you down for revenge are rampant. The snake is the monocled cobra (Naja kaouthia), part of the 30-member true cobra family.
Naja kaouthia measure 100-150cm (max 230cm) and are ubiquitous in Thailand, occurring in every province. They’re also abundant in peninsular Malaysia, Vietnam and Cambodia. Monocled cobras are estimated to cause the highest number of Thai snakebite fatalities annually, while in Bangladesh, they contributed 34% of snakebite deaths from 1988-1989, alongside their cousin the Indian cobra.
The monocled cobra has a more potent LD50 toxicity rating than its cousins, the Javan spitting cobra and king cobra, at 0.4mg versus 0.8mg and 1.2mg respectively. The venom yield is high at an average of 263mg per bite, although luckily, antivenom is stocked at any hospital. Unlike a lazy viper, monocled cobras are fast and snappy. They forage actively by day, which regularly brings them across humanity’s path. Their venom causes not only swelling and necrosis, but has an abundance of neurotoxins, which sever brain signal connections before they can bind to muscle receptors.
| 2 | The monocle ID symbol |
From the front, monocled cobras may be difficult to recognise in a cobra line-up. They have a mixture of black, grey or beige scales, and the customary neck flare of their kind. From the back though, you can observe the instant ID sign, the namesake monocle, a round white circle contrasting with an olive or dark grey hood. Meanwhile, the Indian cobra (Naja naja) has two separate circles, sometimes interjoined, and is sometimes dubbed the spectacled cobra.
Monocled cobras also live in Singapore, Bangladesh, Nepal, and are found in extreme northeast India, in West Bengal province. Here, they have a small area of overlap with the Indian cobra. In most of Thailand, monocled cobras overlap with the smaller Siamese spitting cobra (Naja siamensis). Both are flexible in their habitats, but monocled cobras prefer moister habitats overall, such as rice paddy fields, marshes, swampy forests, and villages near rivers. Siamese spitting cobras appear in drier habitats, such as hillsides and grassy plains.
Monocled cobras are also comfortable in urban jungles, popping up in the heart of Bangkok, George Town and Kuala Lumpur.
| 3 | Eager to bite |
According to this Thai snake expert, monocled cobras are much more willing to strike above 35C, when they become more agitable. However, they’re hardly reluctant in normal temperatures. Monocled cobras will lash out at small provocations. This video shows their classic stance, rearing up straight, then bending their neck backwards so that their head is angled upwards. Strikes commonly strike the thigh, rather than calf or foot, due to their elevated stance.
The monocle sign on their head is almost foolproof, but not quite. Weird morphs have been spotted throughout Thailand, like this fully cream morph spotted in Jharkhand state, India in 2011. Only a few speckles of grey remained, and even the signature monocle marking was missing. It was only identified by throat markings unique to Naja kaouthia, and was a hefty brute at 208cm.
Unlike many rattlesnakes, monocled cobras rarely gather together, except for males and females. Thankfully, you won’t find 10-15 gathered under your front porch or beneath garden tiles. This hasn’t stopped the traditional belief that monocled cobras always live in pairs, and that killing one will inevitably incur the wrath of the other.
| 4 | Profile of symptoms |
2023 saw one of the most detailed monocled cobra studies to date. It involved data from Ramathibodi Poison Centre from 2018-2021, with 1045 patients admitted over 4 years. 485 of these were confirmed as monocled cobra bites, and tons of detailed symptoms were gathered.
Firstly, the local effects. Local swelling surrounding the wound affected 68.0% (330/485) of patients. Necrosis was less common, but still a strong risk, at 21.4% of patients (104/485). This is when healthy tissue sloughs off and dies, involving skin but also muscle, potentially down to the bone. A statistic related to this was that 3.9% (19/485) required skin grafts, and 4.1% (20/485) required amputations. Monocled cobra bites regularly cause lasting deformities.
As for systemic symptoms, one dominated all else: hypertension, which affected 94.8% of victims for whom it was tested. An elevated heart rate (38.2%) and involuntary rapid breathing (27.6%) were also commonplace.
Next up were the neurotoxic symptoms. Ptosis, AKA drooping eyelids, was the most common at 51.5% of patients tested. Bulbar palsy affected 11.1%, a term referring to lower cranial nerve symptoms like slurred speech, difficulty swallowing, poor facial muscle control, etc. Then there was straightforward muscular paralysis, becoming temporarily trapped in your own body. This affected 16.1% of patients (78/485).
| 5 | Respiratory chaos |
Respiratory paralysis wasn’t listed in the study, but its main treatment was common: 48.5% of monocled cobra victims (235/485) were placed on artificial ventilation, with an incubation tube placed down their throat. The duration lasted from 0.5 to 22 days, with an average of 1.65.
The study also contained 54 bites from its cousins: the equatorial spitting cobra (far southern Thailand) and Indochinese spitting cobra (most of Thailand). Swelling affected 72.2% of patients and necrosis 29.6%, fairly similar to monocled cobras. The main difference was that neurotoxic symptoms were less common than with monocled cobras. Drooping eyelids affected 14.8% of patients, muscular paralysis just 1.9%, and only 18.5% of patients were placed on artificial ventilation compared with 48.5%.
The final category was death, and all fatalities were caused by monocled cobra bites, although the sample size was far higher than the spitting cobras. 9 deaths occurred, 1 from ventilator-related complications, and 3 from respiratory failure and hypoxia. Sepsis and complications caused 5 deaths.
| 6 | A lethal roulette wheel |
Naja kaouthia venom is truly a spinning wheel of doom. Many snakes have their specialities, like coral snakes with neurotoxins, or a rock rattlesnake with spontaneous haemorrhaging. But monocled cobras spew out a huge variety of toxins, covering all the bases, making the exact effects extremely difficult to predict, apart from the almost certainty that you’ll be hospitalised.
Naja kaouthia venom contains cardiotoxins, disintegrins, neurotoxins, metalloproteinases and phospholipase A2s. Its primary neurotoxin has been pinpointed as alpha-cobrotoxin, a form of post-synaptic neurotoxin. There’s also the unique kaouthiagin, a metalloproteinase named after the Latin name. This cleaves the clotting agent Von Willebrand factor (vWF) and disrupts platelet aggregation.
Naja kaouthia also has variation in its toxin profile between countries. A 2015 study found that Thai venom samples had the most neurotoxins, at 50% of total toxins, primarily in long-neurotoxin form. Vietnamese samples were well behind at 29% neurotoxins, while Malaysian samples contained the fewest neurotoxins at 18%. Cytotoxins were fewer in Thai venom samples, at 27%, versus 45% for the Vietnam and Malaysia.
| 7 | A Bangladeshi study |
There’s also signs that Bangladesh is particularly dangerous. This 2017 study covered 70 monocled cobra victims, and 58 of those suffered “severe neurotoxicity”. Symptoms included respiratory troubles, muscular weakness and the dreaded “broken neck sign”, when the neck muscles are paralysed so that the person’s head temporarily tilts at a bizarre angle. Most positively, antivenom was found to be effective against these neurotoxic symptoms, more effective than for the cytotoxic local symptoms like necrosis.
One of the cases involved an 18 year old agricultural worker, who was bitten on the right foot by a 120cm monocled cobra which he called “zhawra”. He didn’t vomit or feel faint, but the first symptoms arrived within 1 hour, which were drooping eyelids and weakness. At 90 minutes, he experienced trouble swallowing and trouble speaking. At 2 hours, his neck felt weak and his urine was unusually coloured. At 2.5 hours, his breathing became laboured. The neurotoxic symptoms often arrive before the local necrosis with monocled cobras. His pulse reached 120 beats per minute, and the fang marks were 15mm apart.
Sadly, the boy died, despite artificial ventilation and antivenom administration. His blood oxygen level fell to 23%, and the cause of death was “hypoxic encephalopathy.”: oxygen deficiency to the brain. No cobra species is to be taken lightly.
| 8 | A secret spitter |
Monocled cobras are traditionally filed as a non-spitting cobra, lacking the devilish powers of their neighbour Naja siamensis. But for decades, rumours persisted from villages and dusty scientific logbooks that when pressured, Naja kaouthia did produce the occasional airborne venom discharge. These were disregarded as misidentified snakes, simply confused with Siamese spitting cobras, as is easy to do. That all changed in 2017, on a herpetological expedition in India’s West Bengal State. This lies at the western end of Naja kaouthia’s range, and if any outliers were to happen, it would be here.
When one scientist was peering through a fowl pen entrance at ground level, he was blasted in the face by a monocled cobra lurking on the opposite side. Only a tiny portion entered his eye, but the immediate reaction was excruciating pain. A vile discharge leaked from his eye, and despite swift treatment, he was unable to open the eye for 11 hours. The scientists stomped around West Bengal, and found 120-130 more instances of monocled cobras spitting, particularly in Hooghly, Nadia and Burgwan provinces. They spoke to many West Bengal snake charmers, who had witnessed monocled cobras spitting during the customary de-fanging prep beforehand. These same charmers had never once seen an Indian cobra (Naja naja) spit.
This West Bengal report contrasted with an expedition to Thailand, where 0 out of 100 Naja kaouthia were observed spitting. As with the variation in neurotoxins, certain monocled cobra hotspots may be doubly dangerous. It’s also possible that these are secretly a unique subspecies, with a unique power.
| 9 | Diet: mammals with many side snacks |
As long as they’ve been known, most anecdotal reports have been of monocled cobras loving rodents. In 2011, a study finally confirmed this, using a sample size of 93 prey found in 75 monocled cobras, gathered from Singburi province in central Thailand. Mammals contributed 75.8% of prey by headcount and 65.7% by total biomass (weight). Most monocled cobra stomachs contained a single rodent, but some contained multiple nestling mice or adult mice.
With 3 recorded, birds made up 3.4% of prey, and reptiles contributed seven prey (8.0%). Two snakes were found, and confirmed to the species level: 1 sunbeam snake and 1 rufous-tailed snake, both non-venomous. Other categories included arthropods (9.2%), 2 fish, and an Asian rice frog (Fejervarya limnocharis) eaten by a juvenile in its first year.
The biggest surprise was a healthy serving of bird’s eggs, contributing 11.3% of the monocled cobra’s diet by weight. This included seven eggs of the lesser whistling duck (Dendrocygna javanica), and four eggs of the domestic duck (Anas platyrhuclus), each in varying stages of digestion. These eggs were swallowed whole, unlike a scarlet sake of Florida, which hacks through the shell and slurps the golden yolk out.
| 10 | When 200 broke free |
The study also found several cobra fangs embedded in prey, hinting that they regularly snap off and regrow. Fly larvae were also discovered in two rodents, a hint that this was carrion, already dead and decomposing prey. Like the horseshoe whipsnake of Spain, Naja kaouthia is an occasional necro snake. One prey confirmed in an early study was the tentacled water snake (Erpeton tentacula), one of Earth’s most bizarre snakes, a swamp lover which has bizarre appendages sprouting from its face.
The 2011 study also tested, finding a mean of 23.5 eggs for monocled cobras. An earlier estimate was 21.9 eggs per batch, and well over 40 has been recorded. Monocled cobras aren’t proven to care for newborns, like a ridge-nosed rattlesnake, but they remain with their eggs – most batches are found in the wild with a female guarding them.
Due to antivenom demand, snake farms are popping up where hundreds of monocled cobras are reared. The largest lies in Bangkok and is owned by Thai Red Cross, raising 7 snake species for venom extraction and injection into hyperimmunised horses. But more rickety ones exist, including a Chinese snake farm which burst onto global headlines in 2016, when 200 of its monocled cobras escaped afrind went on a rampage through the countryside of Liuhe district. 150 were caught or killed, but 50 remained unaccounted for, weaving through undergrowth and staying out of sight, possibly hiding in people’s toilets. 1820 monocled cobra eggs had been brought to the Chunyi farm originally, of which 300 hatched. Not surprisingly, the farm was shut down after this incident.