Spiders are carnivorous creatures, and while they primarily feed on insects and other small arthropods, their specific diet depends on the size and species. True spiders commonly consume a variety of insects such as flies, mosquitoes, moths, beetles, ants, and grasshoppers. Spiders may also consume other arthropods, including centipedes, millipedes, scorpions, and even other arachnids like harvestmen or pseudoscorpions. They use their webs or hunting techniques to catch and immobilize their prey. 

Many spider species are cannibalistic and may feed on smaller spiders or even individuals of their own species. This behavior often occurs when resources are scarce or during mating encounters. Larger spider species, such as species of Trichonephila, may occasionally prey on small vertebrates like lizards, frogs, or even mice. However, such occurrences are relatively rare, and the majority of spiders primarily rely on insects for sustenance.

It’s important to note that not all spiders build webs to capture prey. Some spiders actively hunt and ambush their prey, while others use specialized techniques such as jumping or pouncing on their victims. Each spider species has adapted its hunting strategy based on its physical attributes and environmental conditions.