Poisonous substances are not unique to reptiles, amphibians, and fish. The platypus, some shrews, loris primates, and vampire bats use them for different purposes: predation, defense, or competition.

Both the Bengal sloth loris (left) and the platypus (right) are poisonous mammals.

Contrary to certain species of snakes, lizards, frogs and fish, until relatively recently it was not considered that mammals they could also be poisonous. It was not until 80 years ago that the scientific community showed that some of these animals, specifically the short-tailed shrew (Blarina brevicauda), they could store and use this substance. But for what?

During the last decades, scientists have tried to understand the characteristics of its toxin, unusual among mammals and most of the time harmless to humans. However, few studies have focused on them. Among the challenges was above all understand the functions of poison and its evolutionary and physiological implications.

In total, there are only four orders that include poisonous species: Eulipotyphla (solenodonts and some shrews), Monotremata (platypus), Primates (sloth and pygmy lorises) and Chiroptera (vampire bats). But as each of them presents a different strategy for using and managing your toxins, the researchers rule out that there is the same evolutionary origin.

Systems for storing and inoculating venom are key adaptations that have evolved over time and generally facilitate predation or defense, but also the competition between individuals.

These are some of the mammals that, despite their harmless appearance, they are actually toxic.

ShrewShort-tailed shrew (Blarina brevicauda). / Gilles Gonthier

1. Shrews

Among the shrews, the short-tailed ones, along with the Solenodonts of Hispaniola (Solenodon paradoxus), they have an oral poison system, that is, their saliva is poisonous to paralyze Y submit their prey, especially small vertebrates. But the evolution of this toxin in these insectivores it has generated a lot of interest in the scientific community.

The sequencing of the genome of the solenodonts, in danger of extinction, has made it possible to study the origin and evolution of the venom of the eulipotiflanos. The study, recently published in the journal PNAS, not only confirm the hypotensive effect of the venom in the prey to facilitate its capture, but a convergent evolution from four independent origins in these animals.

“The substance evolved by reusing existing saliva proteins, in particular a type of enzyme called kallikrein. Later, other toxins were added to the chemical arsenal that were not of salivary origin, but genes that are normally expressed in other parts of the body, and that ended up being expressed in the venom gland and then evolved for new functions“, Explains Bryan G. Fry, a researcher at the Toxin Evolution Laboratory of the University of Queensland, Australia, and one of the authors of the work.

The poison, which can result painful if the shrew bites a human, is secreted by the submaxillary glands to the base of the lower incisors where saliva flows. This substance appears to have been generated with a clear objective – predation – and its function has remained intact until now.

PlatypusMale platypus inject venom into others through dewclaws on their hind legs. / Adobe Stock

2. The platypus

The platypus (Ornithorhynchus anatinus), an atypical animal in many respects, is also one of the few mammals to possess venom. In addition to laying eggs, having a duck’s snout, beaver’s tail, and otter legs, this unique mammal is capable of injecting venom through its dewclaws on the hind legs.

Its toxin is produced in a different way from other poisonous mammals and has another function, in this case as offensive weapon. Produced in the male’s crural glands, connected to the calcaneal spur of both hind legs through a specific conduit, this capacity is exclusive to males who use it during breeding season. The function of the poison is therefore due to the sexual selection.

“The males stab each other with an intensely painful poison to establish who gets the breeding rights,” details Fry, for whom is “a great example of masculine stupidity and why females of any species live longer ”.

Although not lethal to humans, it can produce “excruciating” pain immediately, which is converted through a complex process in a hyperalgesia —An increased sensitivity to and extreme reaction to pain — long lasting.

Lazy lorisSunda’s lazy loris (Nycticebus coucang). / Adobe Stock

3. The lazy lorises

In the case of lazy lorises like the one in BengalNycticebus bengalensis) Probe (Nycticebus coucang), these small primates Candid-looking Southeast Asians use venom to defend themselves, but in a peculiar way. These mammals lick a gland located in their elbow, charging their comb of teeth, sharp as needles, with a poison with an anaphylactic effect.

In a study, which analyzed the defense objective of this substance, the researchers pointed out that in both the Bengal and Sunda lorises, as well as in pygmies (N. pygmaeus), there is a small inflammation on his elbow, free of fur but barely visible, called brachial gland.

When the animal feels in danger, the gland, which is activated at six weeks of birth, secretes a clear liquid with a strong odor in the form of apocrine sweat. Both males and females adopt at this moment defensive positions with the head bowed and the forelegs raised, after sucking the area of ​​the glands and rubbing against them.

Is oily toxin it is dragged by its sharp teeth, which are used as a resource to inject it into the attacker. Their bites are painful and cause slow-healing wounds. Being a chemically complex substance, scientists believe that it also allows these primates to transmit information through smell about their health, age or nutritional status.

Vampire batsCommon vampires. / Adobe Stock

4. The bats

In the last group of poisonous mammals are the vampire bats, among which there are three species: the common vampire (Desmodus rotundus), the hairy-legged vampire (Diphylla ecaudata) and the white-winged vampire (Diaemus young), which are nourished exclusively by blood.

After its pointed fangs or molars pierce the skin of its prey to extract the blood By licking, the venom is injected through saliva, which contains a glycoprotein, called la draculina.

“These animals use their venom to prevent blood from clotting in their prey and they also dilate the blood vessels so that the blood flows faster, “he explains. Bryan G. Fry of the University of Queensland in Australia. In this way, these chiropterans prevent blood clotting in their victims, allowing continuous feeding.

In this procedure, their saliva is key, once the cut of about 5 mm in diameter and depth has been caused in the prey, which is usually mainly cattle. Its compounds make it possible to prolong bleeding, acting as anticoagulants.

Although millions of years ago there were more species of mammals that could use poison, today only these four groups use it. According to a work, the costs of the production of the venom, the specialized teeth for food and the possible lack of benefit of this toxin prevented it from being generated in larger mammals and thus justify the rarity of this substance in these animals.