Some of these vertebrates have teeth (snakes, crocodiles, and alligators), and certain snakes have poison-inoculating prey.
Associated with the presence of modified salivary glands in venom glands, these prey characterize what we call venomous snakes.
If they do not have inoculant teeth, even having poison glands in their mouths are known as non-venomous. Snakes are predatory and ingest their entire prey without chewing their teeth. The digestive tract is complete, ending in cloaca.
Poison glands present in venomous snakes.
As in amphibians, the heart of reptiles has three cavities: two atria (one right and one left) and one ventricle. The heart of crocodilian reptiles has four cavities.: two atria and two ventricles (such as birds and mammals). However, even in crocodilians there is a mixture of blood types (venous and arterial) that pass through the heart, although to a lesser extent than in amphibians.
So we can consider the circulation of reptiles double and incomplete. As a result, the animals in this group are pecilodermalthat is, they adapt body temperature to ambient temperature.
In the terrestrial environment, temperature variations are greater than in the aquatic environment. To keep body temperature close to the environment, reptiles often use external sources of heat, such as the sun or the hot surface of a rock. It is common to see reptiles exposed to the sun during the day. The term "lizard" is applied to people who lazily lie in the sun, the way lizards do.
When reptiles feel very warm, they usually look for shade. With this behavior they keep the body temperature practically constant, around 37ºC.
Many species of snakes and lizards are useful to humans as they hunt rodents and other animals that harm agriculture and cause disease to humans. Among snakes, however, are species whose venom can be fatal, causing the death of large numbers of people each year.
Loreal Fossa - Orifice in front of the eye
In Brazil, venomous snakes can usually be recognized by the presence of a small hole located between the nostril and the mouth: loreal pit, a heat sensitive sensory organ. With it these snakes detect the presence of warm-blooded animals (birds and mammals), their favorite prey. The loreal pit is absent in the true coral, despite being poisonous.
See the table below for other characteristics used to differentiate a poisonous from a non-poisonous snake.
Long (tunes slowly)
Short (tunes abruptly)
With rounded pupils
With vertical slit pupils
Scales of the head
The criteria used to differentiate between the two types of snakes have exceptions, so they should not be strictly followed. For example, the true coral snake is venomous, however it has no loreal pit and has a rounded head.
To prevent snake accidents, it is very important to:
- Wear boots and leggings whenever walking in environments that are conducive to the presence of these animals, as most bites reach the legs below the knees;
- Wear leather gloves when handling garbage piles, dry leaves, straw or holes to prevent stinging of hands and forearms;
- Be careful when handling piles of firewood, corn or cane and turning over termites, as snakes like to take shelter in hot, humid places;
- Watch out for shoes and boots as venomous animals can take shelter inside them.
In cases of snake bites, seek immediate medical attention. The injured person should receive the appropriate dose of Snake antivenom which contains antibodies (antitoxins) capable of counteracting the toxic effect of the poison. The limb struck by the bite should be kept in a very high and still position, as locomotion facilitates the absorption of poison. Do not place any material on the wound (leaves, coffee grounds, earth, etc.) as they may cause infection, aggravating the situation. Do not cut the bite site with penknives or other uninfected objects as they may cause infection or aggravate the bleeding effect of certain poisons.
Some feared snakes are not even venomous. This is the case of the sucuri, which can reach up to ten meters in length and kills its prey by strangulation. The boa constrictor, which is up to 3 meters long, is not venomous and does not attack the man, fleeing when provoked. The musurana is a non-poisonous snake that feeds mainly on poisonous snakes.
Among the venomous snakes, we can mention the jararaca, jararacuçu, jararaca-ilhoa, urutu, rattlesnake, surucucu, etc. The vine snake, the musurana and the false coral present the poison inoculant prey located in the posterior region of the mouth. This location hinders efficient poison inoculation. Therefore, these snakes pose no danger to man if they can be recognized.
Alligators and crocodiles, as well as snakes, have their skin used in making bags and shoes. Therefore, in the Brazilian wetland, these animals are at risk of extinction. The man has been promoting a major killing and illegal sale of these skins by smugglers and foreign merchants. A consequence of the decrease in the number of alligators in the Pantanal can already be observed: the number of piranhas, of which the alligator is predator, is multiplied. The increase of piranhas is a big problem for the people of the region, who develop their activities in the water (washing, bathing, crossing the river with cattle…).
In addition to the reptiles already mentioned, examples of beings in this group are the tortoise, the jabuti, the chameleon, the iguana, the two-headed snake, the glass snake and the gecko.