All spiders are carnivorous, and insects make up the bulk of most spiders' food. But just about any small invertebrate – including other spiders – is fair game. Even a few vertebrates, such as frogs, fish, birds, and rodents, occasionally find themselves in the fangs of these formidable predators. (You bet there are some big spiders out there!)
Spiders are amazing food-catching machines. Even the most common methods and "tools" they use to make a living – the basic web, for example – are marvels of evolutionary ingenuity. Here's an overview of some of the ways spiders do what they do best.
When most people think of spider webs they probably think of the spoked, roundish, and more-or-less regular constructions called orb webs. Although these beautiful webs may look like they'd take their tiny architects all day to design and build, many orb weavers can whip one out in less than thirty minutes. Most orb web spiders spiders build a new web every day, recycling their silk supply by eating the old web.
Orb webs may be the most elegant of the silken snares, but they certainly aren't the only ones. There are lots of variations on the theme, from elaborate tunnels and tubes to the tangled cobwebs that house spiders build in ceiling corners. There's also the minimalist approach of bolas spiders, which manage to catch their dinner on a single silken line that they hurl at passing prey.
Lurking for Lunch
Web weavers are rather sedate creatures much of the time. But when the vibrations of a struggling victim signals a catch, they spring to life and head for the action. Experience and an oily coating on their feet help spiders avoid getting stuck as they skirt across the threads of their web.
Once a spider reaches its prey, it usually subdues the animal by biting it, injecting a paralyzing venom, and wrapping it in silk – or, conversely, by wrapping it in silk and then giving it a venomous bite. If times are plentiful and the spider isn't particularly hungry, it may save the meal for later. But if it is hungry, it starts digesting immediately – before it even begins consuming it.
Spit and Suck
Pre-digestion is a must for spiders, who don't have a mouthful of teeth to help them break down their food. To start the digestion process, a spider spits up from its intestinal tract a drop of liquid and deposits it onto the prey animal, momentarily marinating it in digestive juices. Then, with help from powerful contractions in its throat and stomach, the spider sucks down a portion of its liquified meal. It repeats this "spit and suck" process until nothing but the hard, indigestible parts of the victim remain.
About half of all spiders don't build webs to catch their meals. Instead, they either lie in ambush for their prey or, in a few cases, they actively stalk it. These webless spiders are often called "wandering" spiders, a reference to the fact that they are less sedentary (though not by much, in some cases) than their web building relatives.
Many wanderers do build a kind of silken nest – either wedged among vegetation or in a shallow burrow – but this nest doesn't serve as a bug snare. Instead, it's a hiding place, or retreat, within which the spider waits for passing prey. When it sees or feels movement nearby, the spider rushes out of its retreat, pounces on the animal, and delivers a paralyzing bite. Then it uses the same basic feeding techniques as web weavers, digesting the animal in advance and sucking in its liquid meal.
Can you guess what the spiders below are camaflauged as? Click on the image for the answer.