LPH Exam Paper Question on the Berg Adder and Effects of Snake Venoms

In the February 2025 LPH exams, the following question was asked in the Habits and Habitats module:

“A berg adder will induce local responses like pain, painful swelling and even necrosis. Define the term “necrosis” as a condition induced by haemotoxic venomous snakes.”

Despite the confusion this question causes, I have developed the thought that this was in fact one of the best questions set in this exam because the multiple contradictions of this question mean that only somebody with confidence in the subject of snake venoms can successfully face it.

Firstly, it is important to be aware that every venomous snake produces all the four types of venom (neurotoxic, hemotoxic, cytotoxic, and myotoxic), but usually only one of them becomes prevalent, while the others are confined to an irrelevant dose. In a family where the general rule is to produce a certain type of predominant venom, some species can break the rule and (evolutionary) end up producing a different predominant venom that better suits their needs. The berg adder is a typical example of a rule-breaking species.

The first part of the question mentions the berg adder (Bitis atropos), a snake of Viperidae family that inhabits rocky areas, mountains and cliffs. The question also mentions several local responses (“pain, painful swelling and even necrosis”) as typical of cytotoxic venom, claiming that they are induced by the bite of this snake. The berg adder is in fact an exception in the adder family. Most of the species belonging to Viperidae family do produce a primarily cytotoxic venom, but the berg adder, in response to its habitat, has developed a mainly neurotoxic venom. This snake, dwelling areas of boulders and cliffs, needs a venom that acts faster than the cytotoxic venom so that that prey they have bitten cannot escape and eventually fall off a cliff, where the adder can no longer retrieve the prey.

Another example of a species where the venom balance does not follow the species type is the Mozambique spitting cobra. This cobra is an Elapidae and most Elapidae produce a predominantly neurotoxic venom. The Mozambique spitting cobra, however, has a predominantly cytotoxic venom to support its technique of spitting venom in the eyes of a potential aggressor. The neurotoxic venom needed to penetrate the lymphatic system of bitten prey would have no effect if sprayed in the eyes. The cytotoxic venom, however, is very aggressive against cell walls and so immediately starts to burn the eyes, which causes the dissuasive and distracting action the snake is looking for.

In the second part of the examination question, instead, the candidate is asked to describe “necrosis” as a condition induced by haemotoxic venom. In fact haemotoxic venom induces a very little necrosis. Necrosis, in fact, is the death of body tissues, induced by the cytotoxic venoms whose proteins attack and destroy the walls of cells. Necrosis can also be the consequence of poor or lack of blood flow in tissue, and haemotoxic venom, causing massive bleeding which can of course reduce the blood flow to certain organs and body areas. In this case, necrosis is just a secondary consequence that occurs when haemorrhages had already done most of the job.

So, to answer the above question properly, a candidate should not just assume that the question contained correct facts. Only a deep knowledge of snakes and their venoms is going to produce a satisfactory response to this question.