Spiders eat more insects than birds and bats combined, so they should be considered one of human's best friends. They play a big role in controlling insect populations.
Spider silk is incredibly strong and flexible. Some varieties are five times as strong as an equal mass of steel and twice as strong as an equal mass of Kevlar. This has attracted the attention of scientists in a number of applied science fields, but up until recently, humans haven't been able to get much out of this natural resource. It's simply too hard to extract silk from spiders, and each spider has only a small amount of it.
Spiders use their silk in a variety of ways, as we will see below, but Orb weavers are the spiders most of us are familiar with - the type that builds webs in trees and bushes and the corners of our ceilings. When the orb web has deteriorated and is no longer useful, many spider species will destroy it, eating up all the threads so it can recycle the raw silk material. Spiders may leave the heavy bridge thread so that they can easily rebuild the web at a later point.
While many spiders use their silk to trap their prey, protect their young or build their nests --- the Bolas spider uses it as a range weapon. These spiders do not spin the typical web. Instead, they hunt by using a sticky 'capture blob' of silk on the end of a line, known as a 'bolas'. First, they attract their prey (usually moths or moth flies) with potent pheromones designed specifically for luring their victims. Then, swinging the bolas around and letting it go, the spider may snag its prey rather like a fisherman snagging a fish on a hook.
The Net-Casting spider also uses its web for other than hanging. She will spin little nets that she will then hold with her front legs, suspended above the forest floor, waiting. When she sees her prey, she uses the net exactly as one would trap a cat with a pillowcase.
Spiders in 8 of the world’s 109 arachnid families can catch and consume small fish.. some of them can even subdue fish five times heavier than they are. At least 18 species can actually catch fish. Some can even swim, dive, and walk on the water's surface. These particular hunters anchor their hind legs to a stone or a plant, with their front legs resting on the surface of the water and then patiently wait to ambush their prey. Just like with their webs, the slightest movement in the water or under their legs can spur them into attack. Beyond water-side hunters, there are several amazing species of spider that can actually swim underwater. They can submerge themselves for 20 minutes to an hour, actually creating a "diving bell" of air that surrounds their book lungs.
Jumping spiders, one of the more common types of spiders world-wide, have the ability to jump great distances -- as far as 50 times their own length. The thing that is the most amazing about these jumpers is that they don't have particularly strong muscles in their legs; they actually spring forward using hydraulic pressure. A powerful muscle in the cephalothorax squeezes fluids from the body into the legs to make them expand.
With more than 5,000 species around the world, jumping spiders are one of the more common spider varieties around. They're characterized by large eyes, which help them spot potential prey at a good distance. In contrast to web-spinning spiders, most jumping spiders hunt sort of like cats, stalking their prey and then springing on them at high speed.
While most spiders have multiple pairs of eyes, vision is a secondary sense in the vast majority of species (the notable exception is jumping spiders, which have excellent eyesight). Most spiders primarily interact with the world through tactile sensation. They are covered in highly sensitive hairs that pick up even low-level vibrations in whatever the spider is standing on (the ground, floor, leaf or web, for example). Many spiders have additional hairs, called trichobothria, which pick up vibrations in the air (sound). In some species of Tarantuala, they can even use their bristles for defense, shooting them off their bodies to embed in their enemies.
The majority of spider species are aggressive and solitary creatures, but there are about 40 species that have something in common with ants and bees. They are social.
Most species of social spiders live in the tropical regions of the world where insect size and density is highest but there are a few in the eastern US. By building a communal web, it is thought that the spiders think to increase their opportunities to catch prey. Having a larger web and multiple spiders to work together to subdue prey allows them to prey on larger organisms that would be impossible if they led a solitary existence. The colonies can grow large enough to take down birds and bats as well as very large insects.
What is also very interesting is that recent studies have shown that social spiders do not do as well as solitary spiders... that raising the young with multiple caretakers has resulted in a higher death rate. It is thought that the more agressive, solitary mothers do a better job of raising their own young than a large community of (hippie)spiders working together.
There are a number of species of spider that do not spin webs, but instead roam the ground. The Wolf spiders and Tarantulas, notably. But there is a subset of wolf spider that builds tunnels, funnels and burrows in order to hide and trap their prey on the ground. These dudes tend to be very non-agressive but when threatened they raise up their front legs in an effort to appear larger and more intimidating to potential predators. That would be enough for me, certainly.
Trapdoor spiders are ground dwellers, with a burrow lined with silk of up to 10 inches in depth and around 1 inch in width - prefers nesting in drier exposed locations. It often has a wafer-like lid on the burrow entrance that they hide behind and spring open, dragging their prey inside when opportunity strikes.
Funnel Web Grass spiders are timid and non-aggressive as well. These spiders are often called grass spiders because they construct their webs in tall grass, heavy ground cover and the branches of thick shrubs. Rarely will a funnel web spider be seen indoors.
Wolf Spiders also create burrows from which they lurk, sometimes with a lid or covered by leaf litter or grass woven with silk as a little fence around the rim. They also rove the ground at night looking for prey, much like the wolf they are named after. It can move very rapidly when disturbed.
Goliath bird-eaters are the world's largest species of tarantula, and considered the world's second largest spider (to the Huntsman - but they still rule in the weight class). Tarantula is a generic name for hairy spiders. This hairy spider has a leg span of 12 inches across, or about the size of a dinner plate or small pizza, and they can weigh 2.5 ounces. Although they are called Bird Eaters, they rarely eat birds... but they do feed on small animals and have been known to fight and kill poisonous snakes.
Arachnids, just like insects, have external skeletons (exoskeletons), which is their skin or shell. When a spider moults it splits open its old skeleton and wriggles out of it, the new skeleton that was growing underneath is soft and pliable, for a short while. The spider, once it is free stretches the new skeleton to allow some room for new growth, the new skeleton then hardens. And, like reptiles, spiders can regrow lost limbs when they regrow a new skeleton.
Spiders moult to grow larger, but when they have lost a limb, their moult takes a considerably longer amount of time to do... leaving them vulnerable for a longer period of time. Tarantulas, being ground dwellers, are the most vulnerable, as their new exoskeletons can sometimes take a few days to harden back to the point where their armor is a defense.