Are spiders insects? No, they're not. Although spiders and insects belong to Phylum Arthropoda, they are two distinct classes (Arthropoda and Insecta). The outermost layer of Arthropods is their skeletal system. There are over 30,000 known spider species, a quarter of the estimated total population of spiders.

Spiders are primitive animals that date back many million years ago. They are natural predators, help control insect populations, and are widespread and abundant.

The term spider is derived from the Old English verb spinnan which means "to spin".

Spiders have two main body parts while insects have three. Spiders, compared to insects, cannot fly. Spiders have eight legs, piercing jaws, simple eyes, anterior abdominal opening in their genitals, and silk spinning organs in their abdomens. Insects, on the other hand, only have six legs, antennae, compound eyes, posterior genital opening on the abdomens, and chewing jaws.

The simple eyes of spiders are not sufficient for them to sense their prey and predators because it it underdeveloped. They make use of vibrations on the surface of their web in sensing an intruder. They possess bristles (distributed on the surface of their bodies) which are tactile receptors that are sensitive to various stimuli like airflow, touch, and vibration. These bristles are part of their exoskeleton and are not hairs.

The spiders utilize tiny claws that are located at the base of their legs as well as notched hairs to help them walk on the webs they weave without sticking to it.

After capturing their prey, spiders cover their victims with digestive enzymes which are released to help digest their victims outside the spider's body. When the enzymes have finished liquefying the their prey, the spider will then suck the juices.

Fossil records of spiders are poor even though they are one of the earliest animals to live on land. Studies have estimated that these animals evolved about four hundred million years ago. The primitive spiders were thick-waisted and live on water. Fossils of Attercopus fimbriungus have shown this spider to be similar to he modern spiders having thin waists, segmentations on their abdomens and have spinnerets that produce silk. It was also learned from this fossil that they lived during the Devonian Period (about 380 million years ago) which is 150 million years earlier than when dinosaurs appeared.

When complete spiders were trapped in sticky ye clear tree resins (amber spider fossils) during the Tertiary Period, it was discovered that modern spiders were similar to those spiders which existed about thirty million years ago.

The spiders belonging to the group Mesothelae are ancient spiders who ar segmented and whose spinnerets are located under the middle of their abdomen as compared to modern spiders whose spinnerets are at the end of their abdomens. It was believed that these ancient spiders live on the ground (clubmoss and fern forests) and prey on other primitive arthropods like millipedes, slaters, cockroaches, and giant silverfishes during mid-late Palaeozoic Period. They use their silk to cover and protect their eggs, line their retreat holes and as a simple web for ground sheet and constructing trapdoors.

The use of silk by the spiders evolved as insect and plant life expanded. The modern spiders (Opisthothelae) showed up more than two hundred fifty million years ago, with spinnerets located at the end of their abdomens. Their evolution was believed to be because of their need for more elaborate maze webs and sheets to capture their preys on the foliage and ground and also to use it as an effective dragline.