To laypeople, the so-called gymnophions can look like a big earthworm, or even some kind of snake – so much so that they are popularly known as “blind snakes” or “Ceciles”. In fact, these limeless animals are vertebrates of the amphibian group, as are frogs and toads. Although they have existed for about 250 million years, blind snakes are still poorly studied, because they live mostly buried and are difficult to find. Thanks to a team of Brazilian researchers, however, they once again received attention from the scientific community. That’s because they are the first known amphibians that show signs of being venomous.
The discovery was made by researchers from the Butantan Institute with the support of Fapesp (São Paulo Research Foundation). Scientists were analyzing the head of the species Siphonops annulatus when they came across large glands, which were connected by a tube to the animal’s teeth, both in the lower and upper jaws. Structures like this are found in venomous animals, which produce poison and use it in prey or to defend themselves. The study describing the discovery was published in the journal iScience.
To this day, no venomous amphibians are known – only poisonous species. Poisonous animals are those that can produce toxic substances, but do not have structures capable of inoculating them. Some species of frog, for example, secrete poison through glands in the skin, which cause damage to anyone who touches or bites the animal. Blind snakes also have poison, and they secrete it through glands in the tail region.
But the structure found in the head of these animals suggests the existence of a venomous mechanism, that is, to inject the poison. Microscope analyzes have shown that these glands originate from tissues other than the tail poison glands, which arise from the animal’s epithelium. The head glands are derived from dental tissue – the same embryonic origin as venom glands found in snakes, which strongly suggests a very similar mechanism.
Blind snakes live underground, digging tunnels and feeding on other animals, such as insect larvae, earthworms and even small lizards. Since they have no limbs, they use a mouthful of teeth to bite and incapacitate the prey, and researchers now suspect that it also uses venom to immobilize and help kill their meals.
Despite the discovery, it is still not possible to say with certainty whether the animal is venomous or not. This is because what has been found are structures capable of inoculating the poison, but it has not yet been confirmed whether the substance that exists in these glands is indeed harmful. A preliminary analysis by the researchers has already found high levels of phospholipase A2, an enzyme commonly present in the venom of snakes, spiders and bees, for example, which is a great indication that the substance is indeed toxic, but subsequent studies are necessary to hit the hammer.
If blind snakes are confirmed as venomous animals, there will be implications not only for the species, but for the general understanding of how the mechanism evolved in animals. These amphibians are much older than snakes (250 million years ago versus 120 million, more or less), which suggests that gymnophions may be the first venomous terrestrial animals on the evolutionary scale. In addition, the finding may be another example of the so-called evolutionary convergence – when different animals develop similar mechanisms due to the pressure of natural selection. Snakes and blind snakes are very distant relatives, but even so, they developed similar mechanisms due to the evolution, which selected the members that had venom, since these are probably better hunters.
Scientists suspect that the possible venomous mechanism of blind snakes is a more primitive version of that of snakes, as it has several small glands with a small amount of substance inside, while snakes have few glands, but are much better supplied.
Now, in addition to analyzing the substance produced by the animals to check if it is indeed toxic, the team also intends to study other species of blind snakes (there are more than 200) to see if the mechanism is something general of the group or something unique to Siphonops annulatus.