Like all animals and humans, spiders have to eat to survive. Spiders are considered carnivorous with one exception, the Bagheera Kiplingi spider, which is a type of jumping spider that is omnivorous, but mainly feeds on plant life. Because spiders eat other living insects and animals that are in most instances much more mobile than spiders, they have developed unique ways of capturing their prey.
To catch a meal most spiders weave webs that are sticky so that insects or in some cases small animals that come in contact with the spider web will become stuck in the web and not be able to escape. The types of webs that spiders weave vary greatly by species and the way they function to capture prey. A brief look at how spiders catch their prey helps us to understand how spiders consume food.
Probably the most familiar spider web, one that is woven between two solid objects, may be woven on either a vertical or horizontal axis. Vertical webs efficiently capture flying prey, sometimes even small birds if the spider is one of a large species. Horizontal webs capture flying prey as it rises from below and crawling prey as well, which may include lizards and mice. The vibrations along the strands of the web, made by the prey trying to escape, alert the spider that dinner is served. There are also spiders that make and live in “diving bell” shaped webs underwater in order to catch minnow fish. Some spiders live in holes in the ground with silken trapdoors that trap passing prey so the spider can drag it down into its burrow. Other spiders actually stalk and “jump” onto their prey.
Once the prey is captured the spider may need to immobilize it or kill it. Once immobile, the hapless prey is bitten to inject digestive fluids and sometimes venom which kill it. Other non-venomous spiders may immobilize prey by wrapping it in silken threads to hold it until they are ready to eat. There is some disagreement as to the method spiders use to consume their food, but this variation could be because of the physical characteristics of the different species of spiders.
It is believed that spiders with weaker jaws will either inject digestive fluids into their prey with the venom if they are a venomous spider, or vomit digestive fluids over the prey. These digestive fluids will liquefy the internal parts of the prey. Once the softer internal parts have been turned into a liquid, the spider will suck the liquid out of the corpse leaving the exoskeleton as a waste. The reasoning behind this theory is that because the digestive track through the waist area of a spider is so narrow, the spider can ingest only liquid forms of food for internal digestion. Some larger spiders may have stronger jaws and are able to actually masticate or chew parts of their prey, including the exoskeleton; however these spiders may also leave parts of the exoskeleton as waste.
The diets of spiders are as varied as are the myriad species of spiders. Spiders prefer to eat only live or freshly killed prey but are not adverse to consuming already dead prey. Spiders are opportunistic predators and will catch and consume any prey that should be unlucky enough to pass within their reach. Spiders can and will cannibalize other spiders of the same species or capture and consume spiders of a different species.
Research into the length of time that it takes a spider to consume its prey appears to be lacking, but logically it would depend on the size and type of prey relative to the size and type of spider. What is known however is that it is not necessary for spiders to eat on a daily basis, neither do they have to eat frequently. Spiders are able to survive for long periods of time without consuming food and some have been known to survive as long as two years without food.