Araneae
Araneae, commonly known as spiders, are an order of arthropod animals that are air-breathing and have eight legs and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of July 2023, over 50,000 spider species have been recorded by taxonomists. However, there has been debate as to the true number of spider species due to the difficulty in identifying them. Some estimates suggest the number of spider species could be much higher, potentially exceeding 120,000.
Characteristics
Spiders are easily distinguished from other arthropods by their eight legs and the presence of spinnerets at the end of their abdomen. They are also characterized by their cephalothorax, which is a fused head and thorax, and their abdomen, which is separate from the cephalothorax. Spiders are carnivores and typically feed on insects and other small invertebrates. They capture their prey using a web of silk, which they spin from their spinnerets.
Environments
Spiders are found in a wide variety of environments, including forests, deserts, grasslands, and caves. They are also found in human dwellings, where they can be both beneficial and annoying. Spiders are generally beneficial to humans because they help to control populations of insects. However, some spiders can be venomous and may pose a threat to humans. The venom of most spiders is not dangerous to humans, but a few species can cause serious illness or even death.
While spiders are adapted to life on land, they have not colonized aquatic environments in the same way as other arthropods, such as crabs and lobsters. There are no true marine spiders, though some species have adapted to living near the water's edge, or in damp environments. Some spider species are able to live in freshwater environments, such as the water spider (Argyroneta aquatica) which can live underwater using a silken bell to trap air.
References
For more information on Araneae, please refer to the following sources: