Many trap insects for food using a sticky web which can be a beautiful spiral or an apparently unorganized mass of threads. Providing food for a spider can be easily done by trapping flies, or other insects, and releasing them into the spider's container. Insects used for food must be alive and not dramatically bigger than the spider. Spiders will not accept dead insects. Prey is injected with poisons that immobilize them.
Some spiders also inject enzymes that liquefy the prey.
Providing an insect once a week should be sufficient. Offer insect prey more often to determine the dietary needs of individual spiders. Water Spiders obtain all of the water they need from the insects they eat but spiders in captivity do need additional water. For ground nesting species, supply a cap filled with water. If the spider is smaller than the cap, add rocks to the cap so that the spider does not drown.