biology zoology blog benno meyer rochow venom

Who is and isn’t poisonous?

Putrefication in the gut

It’s rather funny, but at elementary school, I was neither the smartest nor the strongest, but I was respected even by the fiercest bullies in class. Why? I was the only kid, who was not scared to grab with bare hands one of those big spiders from their orb webs. In most cases, the spiders were too weak to bite through the skin of my hands, but sometimes they did, but it wasn’t at painful at all. However, were they not poisonous?

Well, all spiders have poison glands, but the poison’s potency varies from species to species and the spiders I plucked from their webs usually had trouble biting through the skin of my hands. But how about snakes? We tend to categorize them as venomous and non-venomous. There is good reason to do so, for what we term venomous usually refers to snakes that possess specialized teeth with a canal through which poison can enter the victim that has been bitten by these very teeth. The longest snakes on Earth, with documented maximum lengths of 8 – 9 m, are the reticulated python of South East Asia (Python reticulates) and the anaconda of tropical South America (Eunectes murinus). Both have strong teeth, but lack the special ones that would allow poison to be injected into their victims. These snakes kill not by using venom, but by entangling, suffocating, and crushing their prey to death. Yet, the claim has been made that they, too, produce poisonous secretions. I once placed a lizard into a small bottle with alcohol, but days later bacteria had started to decompose the lizard’s inside, causing the dead lizard to swell up even in the alcohol.

Now imagine a deer or a pig, swallowed by a non-venomous huge snake. The snake does have strong stomach muscles and very aggressive stomach juices containing HCl, pepsin and mucin, but these juices need time to penetrate the fur, skin, bones, muscle layers, etc. before they can act on the ingested animal’s gut and its contents. The digestion of a deer or pig can take months and certainly at the beginning of the process, bacteria inside the swallowed animal through decomposition and gas production will produce toxic compounds, even heat (a ‘cold-blooded’ snake’s gut temperature rises during the period of digestion). To neutralize the toxic compounds, which the putrefying bacteria in the swallowed victim’s body release into the snake’s body, the snake has huge salivary glands. Here the toxic material is stored and slowly broken down. Even anti-poisons may be produced, for extracts of the salivary glands of so-called non-venomous, harmless snakes were apparently potent enough to kill small mammals.

Mechanisms, speeding up the release of aggressive gastric juices into which CO2 enters, have recently been reported from crocodiles, in other words animals that also swallow whole, large animals and need to digest, fur, bones, hooves, etc. before putrefaction poisons the meal. The evolutionarily younger snakes may have inherited part of that system. Why, however, the famous egg-eating snakes like the African Dasypeltis spp. or the Indian Elachistodon spp. cannot simply dissolve the shells of the ingested eggs in their stomach juices and must regurgitate them, I do not know. But what does seem more and more likely is that the venom system in snakes, as well as lizards, stems from a common ancestor, for venom glands in lizards are no longer known only from just one species of lizard (the American gila monster Heloderma suspectum), but have recently also been described from the Komodo dragon (Varanus komodoensis), which, when I visited Komodo Island to take photographs of this largest lizard on Earth, was still believed to infest its victim with virulent bacteria following a bite. Perhaps what we call ‘non-venomous’ snakes have actually evolved from venomous ancestors and not, as often stated, the other way round.

© Dr V.B. Meyer-Rochow and, 2020.
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