Bitten by Leptodeira: Docile creatures with rear fangs
When we think of venomous snakes we tend to think of species like rattlesnakes, fer-de-lance, and adders, which belong to the viper family, or cobras, mambas, taipans, and coral snakes, which are members of the elapid family.
Most other snake species are harmless to humans, but that does not necessarily mean they are not venomous. The largest family of snakes is called the Colubridae. Colubrid snakes, also known as the so-called ‘typical snakes,’ includes species such as the European grass snakes, the North American water snakes and garter snakes, and South American species such as tiger ratsnakes, whipsnakes, and snail-eating snakes.
Although the larger species are capable of inflicting a painful bite, most colubrid snakes are completely harmless to humans.
However, a good proportion of colubrid snakes are often referred to as being rear-fanged, meaning they have a pair slightly enlarged teeth positioned towards the back of the upper jaw below the eye. The enlarged teeth have grooves running down them that channel toxins in the snakes prey through a chewing action. There have been a handful of documented deaths, the most infamous of which involves renowned herpetologist Karl Schmidt who died in 1957 from a bite from a boomslang at the The Field Museum of Natural History in Chicago.
Are rear-fanged snakes harmless?
It is still the case that most rear-fanged snakes can do no real harm to humans, but our knowledge about the effects of the toxins of rear-fanged colubrids is still fairly limited. This is due mostly to the fact that people rarely get bitten by them, and when they do the bites tend to be defensive in nature, a quick bite and release, and this style of bite does not give the snake enough time to chew and deliver a substantial dose of toxins.
In most cases people who are unfortunate enough to get bitten by most rear-fanged snake species, experience mild tingling sensations and localised swelling around the bite.
But what happens if a human receives a full feeding bite from a rear-fanged colubrid?
The answer is in most cases, we simply don’t know.
Encounter with Leptodeira frenata, rainforest cat-eyed snake
Back in 2013, I was unfortunate enough to make a mistake with a rear-fanged colubrid, a rainforest cat-eyed snake (Leptodeira frenata) whilst on a conservation expedition with Indigo Expeditions (then known as Project Chicchan) in Laguna del Tigre National Park.
Rainforest cat-eyed snakes are a medium sized snake with maximum recorded length of around 70cm. The genus to which they belong, Leptodeira, are widely accepted to be docile creatures and, although they have rear-fangs at the back of the mouth and are mildly venomous, they are not considered dangerous to humans, and the published literature at the time suggested that only mild local swelling results from their bite.
A few nights into the expedition we encountered the rainforest cat-eyed snake, and while I was showing the snake to some park guards, the snake bit me on the middle finger of my right hand. At first I was merely surprised as the snake was quite calm in my hands and not showing any signs of feeling threatened. I thought it would let go fairly quickly as is normal for a defence response. It soon became clear that this was not going to be the case. The mistake I had made was that I had been handling a frog a few minutes previously, the favourite food of cat-eyed snakes.
I was receiving a feeding bite after the snake had mistaken my finger for a frog!
The snake had a very strong hold on my finger. It was about this time that I started to feel a burning sensation in my finger. At this point the snake was carefully removed so not to damage it and placed in a cloth bag. It had been no more the 60 seconds. What followed over the next 24 hours demonstrates how little we actually know about snake venoms – in particular the toxins of rear-fanged colubrids.
Within 10 minutes, my finger had started to swell and was intensely painful. The burning pain and swelling increased during that first night – it was the most intensely painful night of my life. In the light of the next morning we were all shocked to see the swelling had developed into blood blisters covering most of my middle finger and the swelling had almost reached my elbow! It looked more like a viper bite than the mild swelling described in the literature.
Thankfully, over the next few weeks the swelling reduced and my finger (eventually) returned to normal, with no lasting damage done! Knowing that this reaction had not been recorded for this species, or genus before, we diligently recorded the symptoms and our first aid procedures all the way through.
As I said before, we know very little about rear-fanged snake venoms and their effects so this information is important to document. Excitingly, this case study has been written up into a medical paper, in collaboration with Scott Weinstein who is a specialist in the effects and treatment of snake bites.
The account has now been published in Weinstein et al (2014) – click to download .pdf.
Although academically this is all very interesting, and goes to show how little we know about snake venom, it is not an experience I wish to have ever again – once in a lifetime is enough! And of course remember that most snakes are not capable of doing us harm, and any snake will bite us if we give the animal no other option but to defend itself – or if we are mindless enough to handle a food item before handling a snake!
Ultimately, if we leave snakes alone, they will leave us alone.
Indigo Archives: First Published 4 March 2014
Elapid snakes like the spectacled cobra (left) and coral snake (right) have enlarged fixed fangs at the front of their mouth on the upper jaw.
Non-venomous colubrid snakes like the tiger ratsnake (left) and neotropical whipsnake (right) are harmless to humans, although due to their size they can give a painful bite.
Some colubrid snakes like the Mexican parrot snake (left) and false barba amarilla (right) have enlarged teeth at the back of the mouth. Most rear-fanged snakes are harmless to humans.
The effects of bites from rear-fanged colubrid snakes can vary hugely. This bite from a rainforest cat-eyed snake (Leptodeira frenata) caused swelling from the bite to the elbow as well as a large blood blister on the bitten finger. The account has now been published in Weinstein et al (2014) – click to download .pdf.
This blog is intended solely to highlight the intricacies and risks of working with snakes in the field.
It is not intended to be used either as an identification guide, or a guide to snake handling.
Indigo Expeditions will not be held responsible for any harm sustained by who handles snakes in an attempt to identify them.
Please ask a professional to help!