[Photo] Can you imagine yourself holding this tarantula? CREDIT: Shane Wilson Link | Shutterstock

All spiders are predatory eight-legged creatures that have organs to spin silk at the back ends of their bodies. They are the largest part of the arachnid family, a group that also includes scorpions and ticks. Spiders all have the ability to bite with venom-injecting fangs to kill prey and nearly all of them are poisonous (even if it’s just a little).

Beyond that, there are many different kinds of spiders – just about 40,000 types living in all continents except for Antarctica. And they’re not newbies: fossilized spiders have been found in Carboniferous rocks dating back 318 million years.

Spiders capture prey using a variety of methods. They can trap small insects in sticky webs, lasso them with sticky bolas, or use their vibration-sensing skills to chase prey down. Spider guts are too narrow to take solids, so they liquidize their food by flooding it with digestive enzymes and grinding it up with short appendages.

Spider bites

All spiders can bite, and most of them do no more harm to a human than a bee sting or a mosquito bite. Most spiders with a life-threatening bite are quite shy and only attack when they feel threatened. In the 20th century, there were only about 100 deaths from spider bites.

Spider venoms work on one of two fundamental principles; they are either attack the nervous system, or attack tissues around the bite – both methods can shut down organs in extreme cases.

Researchers are investigating novel uses for spider venom, from an eco-friendly alternative to pesticides to treatments for Alzheimer’s disease, cardiac arrhythmia and strokes. In addition, spider silk has lots of engineering uses, from body armor to optical communications.

Arachnophobia

Humans have long had a tumultuous relationship with the eight-legged critters. Arachnophobia, or fear of spiders, is one of the most common phobias. Some statistics show that 50 percent of women and 10 percent of men have the fear. Evolutionary biologists surmise that a modern fear of spiders may be an exaggerated form of an instinctive response that helped early humans to survive. Other scholars think that spider fears began in the Middle Ages, when spiders became a cultural scapegoat for inexplicable epidemics of the time, like the plague.

Three suborders

Spiders, which make up the order Araneae, are divided into three suborders, Mesothelae, Mygalomorphae and Araneomorphae:

Mesothelae: These are the small, light descendants of the most ancient types of spiders, and their living relatives reside in southeast Asia, China, and Japan. They live in silk-lined burrows with trapdoors, and lack venom glands – though they do have the mechanism to express venom through their fangs.

Mygalomorphae: These spiders are generally heavily-built and hairy, like tarantulas. They live in burrows underground, and can prey on creatures as large as frogs, lizards, and snails. A few species build webs, but it is not very common. Although most spiders live for at most two years, many mygalomorph spiders can live up to 25 years in captivity. The largest tarantulas have a leg-span of ten inches.

Araneomorphae: These are the most common of spiders, making up more than 90 percent of all the species. They build webs and have fangs that close together like a puzzle, instead of the Mygalomorphae fangs that move in parallel with each other. Some of the most interesting species include the only known vegetarian spider, the Bagheera kiplingi, as well as the most venomous spider, the Brazilian wandering spider. Scientists have found that the spider only needs to inject 6 micrograms of its venom to kill a 20-gram mouse, and a full venom load is more than ten times that. People have died from a wandering spider bite after antivenom has been administered.

— Katharine Gammon