Spiders

Spiders are a very broad group within the arachnids, and this article is all about them. But before diving in, let’s clarify one thing: What exactly are arachnids?

What are arachnids?

Arachnids are invertebrate animals included in the large group of arthropods, the same group to which insects belong. This group includes spiders, scorpions, harvestmen, mites, and solifuges.

All arachnids have their bodies divided into two main segments: the prosoma (cephalothorax) and the opisthosoma (abdomen). They also have four pairs of legs.

Important species of spiders

Now that you know what arachnids are, let’s talk specifically about spiders.

Spiders are the most numerous group among the arachnids, with around 50,000 species distributed around the world. Some important species include orb-weaving spiders, golden orb-weavers, nursery web spiders, jumping spiders, and tarantulas. Below, I’ll briefly describe each one.

Orb-weaving spiders

The suborder of araneomorphs includes the largest number of species and also has one of the widest geographic distributions. There’s no doubt that this wide distribution is the main reason for the large number of species in this arachnid family. Different environmental conditions in various habitats have forced these spiders to develop diverse ecological and morphological characteristics. Still, all species share common traits that allow them to be classified as members of the same spider family. Their specialization in capturing flying insects has largely determined their habitat.

Golden orb-weavers

The nephilid family (Nephilidae) is a small group of only four genera within the large suborder of araneomorphs. Nephilids tend to prefer tropical and subtropical regions, except in certain specific cases where areas located in higher or even mid-latitudes are excluded.

Nursery web spiders

These spiders are extremely voracious, requiring a high abundance of insects, other invertebrates, or even small vertebrates in their habitat. For this reason, pisaurids are especially common in temperate and tropical regions, where humidity and temperature conditions support a higher population of small animals for them to feed on. However, their adaptability has allowed them to thrive in areas that aren’t particularly humid, such as parts of North America or South Africa.

Jumping spiders

Salticids are very resilient creatures. Neither heat, cold, nor humidity stops these spiders when prey (usually insects) is plentiful. Their adaptability relies largely on behavioral strategies: in hot areas, they can find cooler spots, while in colder areas, they seek shelter from freezing temperatures. The same applies to humidity. They can even survive the coldest winters by creating microhabitats within their silk nests, where they remain until the mild temperatures of spring return.

Tarantulas

Completely covered in hair and equipped with large venomous chelicerae that point forward, tarantulas of the theraphosid family (Theraphosidae), also known as mygales, bird-eating spiders, or monkey spiders, are arguably the most fearsome-looking. Several factors influence their presence in a particular area. One is the abundance of prey—they are voracious predators requiring lots of food for proper development, although some have been known to survive for over two years with only water and no food. This brings us to another crucial factor: humidity. Tarantulas require ambient humidity, even though they often live in relatively dry and arid environments. To maintain proper moisture and temperature, they dig tunnels that preserve nearly constant conditions.

Anatomy of spiders

Now that I’ve talked about the most important species, let’s go over their anatomy. As mentioned earlier, spiders have four pairs of legs and their bodies are divided into two main segments. They also have pedipalps, which are appendages with a sensory function. In addition, they possess chelicerae, which are mouthparts used to grasp food and are associated with glands that secrete venom. Their diet is very diverse, ranging from small insects and other spiders to reptiles, amphibians, birds, and small mammals.

Important facts about spiders

To wrap up, here are some important facts:

• Arachnids have been present on Earth for over 400 million years.
• Some spiders have adapted to aquatic environments, like Argyroneta aquatica.

And with that, this article on spiders comes to a close.

Bibliography

All information was taken from the book “Amazing Bugs” by National Geographic.