Venomous Snakes: A Quick Reference Scale for Assessing Bite Severity

By César Barrio Amorós1 and Santiago Ayerbe2

1Herpetologist, CRWild (Costa Rica).

2 Toxinologist CEVAP/UNESP (Brasil), Pediatra Unicauca Popayán (Colombia), Intensivista Hospital Militar Central, Bogotá D.C. (Colombia).

Summary

We present a straightforward identification scale (ranging from 0 to 10) designed to quickly assess the potential impact of a snakebite based on the species involved. This scale allows for a simplified understanding of the medical significance of different snakebites. For instance, a bite from a medium-sized aglyphous snake (Mastigodryas) causing only a superficial wound with no medical importance would rate as a 2 on the scale. In contrast, a bite from a large viper (Lachesis) delivering a significant amount of venom, posing a life-threatening risk without immediate treatment, would rank as a 10.

Snakes are commonly categorized as venomous or non-venomous, but the reality is far more complex. Among venomous snakes, there are at least three distinct methods of venom delivery, and many species exhibit mechanisms that are not yet fully understood.

Snake dentition is typically classified into four main types:

Scientific illustration showing the four main types of snake dentition: aglyphous, opisthoglyphous, proteroglyphous, and solenoglyphous. If you would like any modifications or additional details, please let me know.

Oxybelis fulgidus , Costa Rica. Opisthoglypous. Toxicity level 6.

1. Aglyphous:These snakes lack specialized venom-injecting fangs and possess only regular teeth. Examples include boas, pythons, and many common non-venomous snakes, as well as blind snakes.

2. Opisthoglyphous:These snakes have enlarged, grooved fangs located towards the middle or rear of the upper jaw, which help guide venom into prey. Some species, like those in the subfamily Xenodontinae, have particularly prominent rear fangs. This dentition is common among many members of the Colubridae and Dipsadidae families, including genera like Oxybelis, Leptodeira, Phylodryas, Clelia, and Sibon. These snakes are often known as racers, snail-eaters, false corals, and false vipers.

   
   

   

   Bothriechis lateralis. Costa Rica. Solenoglyphous. Severity level 9. Photo: Cristian Porras Ramirez.

3. Proteroglyphous:These snakes have short, fixed fangs located at the front of the upper jaw. The fangs have a semi-enclosed venom duct for efficient venom delivery. This dentition is characteristic of the Elapidae family, which includes cobras, coral snakes, sea snakes, taipans, and mambas.

4. Solenoglyphous:Solenoglyphous snakes possess long, hollow, hypodermic needle-like fangs located at the front of the upper jaw. These fangs are mobile, allowing them to fold against the roof of the mouth when not in use, and are replaceable. This fang type is found exclusively in the Viperidae family, which is divided into two subfamilies:

   • Viperinae (Old World vipers): Includes genera like Vipera, Cerastes, Bitis, and Daboia.

   • Crotalinae (pit vipers from the Americas and parts of Asia): Includes rattlesnakes (Crotalus), fer-de-lances (Bothrops), bushmasters (Lachesis), and others like Bothriechis, Bothrocophias, Atropoides, Agkistrodon, and Porthidium.

     
     

It is crucial to understand that when a bite is caused by proteroglyphous or solenoglyphous snakes, the only way to ensure survival is to seek immediate medical attention at the nearest hospital. Prompt administration of the appropriate antivenom is essential:

• Polyvalent Bothropic-Crotalic-Lachesic Antivenom for bites from Viperidae (e.g., pit vipers, bushmasters, rattlesnakes).

• Polyvalent Anticoral Antivenom (Antielapid or Antimicruric) for bites from Elapidae (e.g., coral snakes).

In contrast, bites from aglyphous snakes (such as boas and pythons) are non-venomous, and the severity of the injury depends on the size of the snake and the extent of the bite. In many cases, the bite may be as harmless as a superficial scratch (similar to a kitten’s scratch). However, bites from larger constrictors like boas, anacondas, or pythons can result in deep lacerations that may require medical care, including debridement and sutures.

Opisthoglyphous snakes present a unique challenge. Many species in this group possess venom that is poorly studied or entirely undocumented, leading to uncertainty about the potential effects on humans. Reactions can range from mild to severe, depending on the species and individual response.

For instance, a bite from a Bothrops asper (commonly known as the fer-de-lance) can produce vastly different outcomes depending on whether the snake is a juvenile or adult, how much venom is injected, and the physical condition of the person bitten.

A Scale for Assessing Snakebite Severity

To help classify and assess the severity of snakebites, we have developed a scale based on scientific literature, as well as our empirical and medical experience. This scale applies to snake species from Costa Rica and Colombia, and can be extended to other regions within the Neotropics.

🔵Snakebite Severity Scale (Low Severity: 0–4).

Level	Name	Description	Treatment	Examples
0	No Medical Importance	Does not bite. No adverse effects.	None	Imantodes, Sibon, Dipsas, Tantilla...
1	Harmless Bite by baby or juvenile colubroids	Does not break the skin.	None	Chironius, Spilotes, Drymarchon...
2	Minimal Involvement. Bite by moderate colubroids	Small epidermal break.	Wash with soap and water	Mastigodryas, Lampropeltis...
3	Mild Tissue Damage by large colubroids or moderate boids	Deeper wound with minor bleeding.	Clean, disinfect, tetanus shot	Phrynonax, Corallus, Epicrates...
4	Moderate Laceration by large boids	Heavy bleeding from constrictors.	Urgent cleaning, stitches, tetanus shot	Boa, Eunectes, Python

🟡 Snakebite Severity Scale (Moderate Severity: 5–8).

Level	Name	Description	Treatment	Examples
5	Mild Envenomation by Aglyphous colubroids	Slight swelling or redness.	Medical eval, antihistamines, antibiotics	Erythrolamprus (Liophis), Spilotes sulphureus
6	Mild Envenomation (Opisthoglyphous)	Tingling or mild stinging.	Monitor for allergic reactions	Leptophis, Oxybelis, Rhinobothryum
7	Moderate Envenomation by Opistogliphous	Localized swelling, pain, numbness.	Medical evaluation, pain management	Leptodeira, Coniophanes, Helicops...
8	Severe Envenomation by opistogliphous	Hemorrhage, necrosis, extensive edema.	Immediate medical care, possible antivenom	Phyllodryas, Chlorosoma, Thamnodynastes...

🔴 Snakebite Severity Scale (High Severity: 9–10)

Level	Name	Description	Treatment	Examples
9	Severe Envenomation (Viperidae/Elapidae)	Severe local/systemic symptoms (necrosis, paralysis).	Hospitalization, antivenom, intensive care	Atropoides, Bothrops, Micrurus, Hydrophis
10	Life-Threatening Envenomation	Almost certain death without immediate care.	Emergency Hospitalizationantivenom, ICU support	Micrurus (<4h), Bothrops/Lachesis (<24h)

It is important to take in count how to differentiate the terminology: when it is said that a snake is venomous, that does not mean it must be dangerous, and vice versa. A snake being dangerous is not the same as being venomous. An opistoglyph snake of scale 6, 7 and 8, even many vipers and elapids of scales 9 and 10 do not show any aggression. They do not want to bite unless they are forced, so they should not be considered dangerous, but rather "ta take care of." You have to keep an eye on them, because their venom can potentially affect a person's health or even life if they bite. And on the other hand, there are very aggressive snakes on scale 1, 2, 3 and 4 that do not have venom, so they do not present a danger of death, but they do present the possibility of minor to serious injuries (depending on the size and depth of the wounds). An emperor boa with a bad temper can cause more danger than a bushmaster. The danger always disappears when any of these calm organisms are left alone.

Imantodes cenchoa, Costa Rica. Opistogliphous. Severity level 0

Chironius grandisquamis baby, Costa Rica. Agliphous. Severity level 1

Mastigodryas melanolomus, Costa Rica. Agliphous. Severity level 2

Phrynonax poecilonotus adult, Costa Rica. Severity level 3

Corallus ruschenbergerii, Costa Rica. Severity level 3

Eunectes murinus, Colombia. Severity level 4

Boa imperator, Costa Rica. Severity level 4

Erythrolamprus aenigma, Venezuela. Severity level 5

Oxybelis fulgidus, Costa Rica. Severity level 6

Leptodeira rhombifera, Costa Rica. Severity level 7

Chlorosoma viridis, Venezuela. Severity level 8

Micrurus diutius, Venezuela. Severity level 9

Metlapilcoatlus mexicanus, Costa Rica. Severity level 9

Cerrophidion sasai, Costa Rica. Severity level 9

Bothriechis nigroadspersus, Costa Rica. Severity level 9

Bothrocophias microphtalmus, Ecuador. Severity level 9

Hydrophis platurus xanthos, Costa Rica. Severity level 9

Micrurus surinamensis, Bolivia. Severity level 10

Bothrops asper, Costa Rica. Severity level 10

Lachesis muta, Bolivia. Severity level 10

Literature.

Ayerbe-González, S.: Serpientes, Accidentes y Soluciones. 1a Edición, 2021, 116 p. ISBN: 978-958-49-24-87-2 www.ayerbedocserpientes.com 

Ayerbe-González, S.: Accidente Ofídico, Cap. XIX, pp. 4081-4134 en: Vargas-Uricoechea et al, Eds.: Texto de Medicina Interna, 2a Edición, 2021, 4335 p. Asociación Colombiana de Endocrinología y Diabetes, Dpto. de Medicina Interna, Universidad del Cauca. ISBN: 978-958-99814-9-8. Gamar Editores, Com. Ed. E.U.