The animal has eight legs, an open circular system, an exoskeleton and is capable of producing silk. The body is divided in two: in the cephalothorax are the mouth, stomach and brain, while in the abdomen are the heart, lungs and reproductive organs. These are the basic characteristics, but there are many variations and differences between the more than 40,000 species that make up the order Araneae. Smaller spiders generally produce suspended webs, while tarantulas (also called “tarantulas” in English-speaking countries) build burrows in the ground and attack passing prey. There are spiders of different sizes, capable of preying on everything from small insects to birds and rodents. But few are dangerous for humans: in Brazil, out of 4 thousand registered species, only three types usually attack people: the brown spider, the armadeira and the black widow.
1) GIVING THE shivers
Most have four pairs of eyes, but some species have fewer or none at all. The level of vision varies, but most see little more than shadows. This is not a problem, because this sense is secondary: the hairs on the body, supersensitive to movements on surfaces and to the wind, serve to orient it.
2) COME PRO ABRAÇO
All species have four pairs of legs. In many of them, there are several small hairs at the ends, whose ends are concave, helping the animal to adhere to any type of terrain. Certain species of crabs also use them as a defense method, shaking their legs to loosen barbed hairs. A curiosity: spiders die with their legs closed because this is an almost automatic muscle movement. Opening them requires pressure from the circulatory system.
(Thales Molina/Strange World)
3) INSECT SHAKE
The ones that make webs wait for the prey to fall there. Those that hunt on the ground bury themselves in burrows and wait for a victim to pass by. Both use chelicerae, a pair of venomous fangs. After paralyzing or killing the victim with a neurotoxin, the spider spews digestive enzymes that liquefy the prey’s organs. Then suck the snot out of your mouth. Few spiders have potentially fatal venom for humans. Even in these cases, the risk of death is low.
4) MOUTH CLAWS
The two elongated parts at the front are not legs but pedipalps, part of the spider’s mouth. They serve to grope the path and the objects that the animal finds, in addition to helping to weave webs and grab prey. They are also useful in reproduction: the male covers them with sperm and introduces them into the female’s genitals.
5) BREAKING THE SHELL
Like other invertebrates, spiders have an exoskeleton, an outer layer that helps protect the body and keep it from drying out. As it does not expand, the exoskeleton is constantly changed as the animal grows. During the first three years of life, baby crabs exchange four times a year.
(Thales Molina/Strange World)
6) CREAMY INTERIOR
There are no veins and arteries: the spider’s body is flooded with the substance hemolymph (equivalent to blood), which carries nutrients and oxygen – it is the so-called open circular system. The heart is a long tube with valves at the ends to pump out fluid, while the lungs are connected to an opening in the body. Air enters and passes to the hemolymph via diffusion.
7) HORDE OF HEIRS
After mating, females can store the male’s sperm for months until they ovulate. When this happens, the eggs produced number in the hundreds. The females wrap them in a cocoon of silk, the ootheca, which is kept in leaves, stones or in the web or burrow itself. Some species carry the cocoons close to the body.
(Thales Molina/Strange World)
8) SOFT ON SILK
Every spider produces silk, although not all spiders make webs. Material is secreted by pairs of glands in the abdomen and expelled by organs called spinnerets. (image above). Each spider can combine the action of the glands to produce different varieties of silk: the normal one for walking on top, the sticky one for catching prey, one for lining the eggs, etc. Spiders also use silk to leave tracks, making it easier for them to navigate. Females deposit pheromones in these tracks to attract mates.
network of intrigues
Learn how the arachnid creates its web pattern
– (Thales Molina/Strange World)
I) From some suspended point, the spider releases a silk thread and waits for it to hit somewhere. When it rolls over, it holds the line on both sides
II) The animal walks on the thread releasing another, looser one. From there, descend to the ground to secure the web’s third and final support point.
III) A triangle is formed by joining the sides. The spider creates several threads from the center of the web and connects them on the sides.
IV) All silk used so far was non-sticky, so the arachnid could walk on it. With sticky silk, it weaves spirals in the center, where future prey will be captured.
SOURCES Book The Private Life of Spidersby PD Hillyard, and websites How Stuff WorksUniversity of Kentucky and Australian Museum; CONSULTANCY Samuel Paulo Gióia Guizze, biologist at the Butantan Institute