AMNH \ N. Duperre
A goblin spider claw as seen under a scanning electron microscope. Since 2006, the number of them described has doubled.
By
updated 7/25/2012 12:27:33 PM ET 2012-07-25T16:27:33

Spiders live on every continent, except Antarctica, and in many environments, from rain forests and deserts to studio apartments.

As familiar a sight as these eight-legged creatures might be, there is plenty we don't know about them.

Scientists have described about 43,000 species of spiders, and Norman Platnick, the American Museum of Natural History's "spiderman," estimates that just as many remain to be discovered. 

"Because these are only estimates, people disagree," Platnick, the museum's curator emeritus of invertebrate zoology, said of estimates of the unknown species. "I have argued that we are basically halfway through (identifying the world's spiders). Some of my colleagues think I am being way to optimistic and we are closer to only 20 percent through." [ Creepy, Crawly & Incredible: Photos of Spiders ]

To figure out how many species remain to be discovered, scientists often look to museum collections. Because finding and collecting a specimen takes much less work than figuring out what it is, Platnick said, these collections can accumulate unidentified specimens.

The spiders and other arachnids known to science so far are amazingly diverse. A new exhibit opening Saturday at the New York City museum explores this diversity and offers visitors the chance to get up close with live spiders and a few of their close relatives.

These include one of the largest spiders, the goliath bird eater whose prey includes snakes, mice and frogs; the western black widow, one of the few spiders poisonous to people; as well as other arachnids, including the desert hairy scorpion and the skunklike giant vinegaroon, which sprays a vinegarlike chemical from its abdomen when disturbed.

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Live goblin spiders, which Platnick is currently studying, are not on display. Typically about 0.08 inches (2 millimeters) long, these spiders are easy to miss, and as a result were a particularly poorly known spider family. In 2006, Platnick and collaborators from around the world began a Planetary Biodiversity Inventory focusing on the goblin family, Oonopidae. At the time, fewer than 500 species — an estimated 20 percent of the family's actual diversity — had been described. Today, that number is more than 1,000, according to Platnick.

Improvements in microscope and imaging technology have made it much more realistic to study tiny living things, he said. Most tiny spider species live on the ground, so to find them researchers must scoop up soil and leaf litter and sort through it using sifting or funneling devices and by hand. Some have also been found living in tree canopies.

Like their spider relatives, many scorpions remain unknown to science, said Lorenzo Prendini, a museum curator who studies scorpions.

About 2,000 species of scorpions have been described, but "there may be at least double or probably triple the number of species remaining to be discovered," Prendini said. "I say that because whenever we go to an area, let's say in the southwestern United States or South Africa or Australia that are relatively better known for scorpion fauna, and we survey the area thoroughly and using a variety of modern techniques we double or triple the number of species in the area."

Extrapolating out to the rest of the world, he estimates there are between 4,000 and 7,000 scorpion species on the planet.

It's not clear where scorpions fit in the arachnid's family tree, since analyses relying on anatomical or genetic data show scorpions branching off from other arachnids at different points in Arachnida's evolutionary history.

The relationships among scorpions themselves are still being resolved, and have relevance for much broader questions.

"Because scorpions are so old as a lineage, as I mentioned 425 million years old, and because they don't move around much, they are a very good group for understanding how the Earth evolved geologically and climatically over time," he said.  

The exhibit SpidersAlive! is scheduled to run through Dec. 2 at the American Museum of Natural History in New York.

Follow Wynne Parry on Twitter @Wynne_Parry   or LiveScience @livescience. We're also on Facebook  and Google+.

© 2012 LiveScience.com. All rights reserved.

Explainer: Eight insects with the 'ick' factor

  • Warren Little  /  Getty Images file

    Many insects provide humans with unheralded services such as pollination, sustenance, and pest control, but some of them gross us out — or worse. Take dung beetles such as the one shown in this image, for example. As their name implies, the insects process feces for their livelihoods. The service helps reduce fertilizer costs on grazed agricultural lands and cuts down on the number of flies and parasites the piles of manure would otherwise attract. But a life of dung? Ick.

    Click the "Next" arrow above to learn about seven more insects with "ick" factors that make us squirm, or much worse.

    — By John Roach, msnbc.com contributor

  • Head lice, the annoying itch

    Sean Gallup  /  Getty Images file

    For moms and dads, the thought of head lice can sow panic at home. School-age kids are prone to pick up the feared infestation of the sesame-seed sized insects in packed classrooms. The critters latch onto hair follicles and feed on tiny drops of blood. At first sight of head lice, many school nurses send infected — and itchy — students straight home. And that's when parents freak out, lathering their kids with shampoos, gels and creams in an effort to kill the lice. However, some lice are proving resistant to the treatments, leaving parents scratching their heads over what to do.

  • Crabs, lice of another kind

    James Castner  /  University of Florida

    Adults, perhaps in the kid-making stage, are also panicked by another kind of lice: crabs. These critters nest in pubic hair and are often transmitted in the course of sexual intercourse. Crab-inspired panic attacks, however, might be on the way out. Researchers at the University of Leeds in Britain noted a decline in crab infestations, first among women and then men, reported at their clinic. The researchers speculated in the journal of Sexually Transmitted Infections that the decline is due to the popularity of the so-called Brazilian bikini wax, which removes most pubic hair, The Associated Press reported.

  • It's getting harder to stop the bedbugs from biting

    Scherzinger Pest Control

    The adage about bedbugs is getting harder to follow, according to entomologists and pest control experts who have noted an uptick in infestations of the blood-sucking insects. Heavy use of insecticides such as DDT all but eradicated bedbugs from the U.S. by the late 1960s, but international travelers appear to have re-opened the door and now, media reports suggest, bedbugs are back with a vengeance. The insects attack warm bodies in the middle of the night and then retreat to dark crevices behind headboards and mattresses. Telltale signs of their presence include pepperlike fecal spots and shed skins.

  • Cockroaches have few fans

    Science

    Garbage-loving, foul-smelling and house-infesting cockroaches have few admirers beyond Disney-Pixar's animated robot Wall-E, whose only friend on a post-apocalyptic Earth is, naturally, among the world's most enduring insects. The notoriously difficult-to-kill bugs can spread disease and cause allergies. Researchers are hoping baits that mimic the pheromones females give off when they are ready to mate can at least give humans an edge in the battle for pest-free environments. In this image, a female cockroach at upper right attracts three males with her scent.

  • Ticks can make people bug out

    AP file

    Ticks, although not technically insects (they're arachnids like spiders and mites), make some people bug out. The critters crawl onto hosts such as dogs and people and burrow in their heads to suck blood. Ticks can go undetected for days, ample time to spread sometimes fatal illnesses such as Lyme disease and Rocky Mountain spotted fever. Prevention requires application of insect repellant when outside and regular body checks for potential bites. If a tick is detected, experts advise not to panic, but to expeditiously remove the tick by grasping it with tweezers as close to the skin as possible and pulling upward with steady, even pressure. A brown dog tick is shown here.

  • Fleas no fun for Fido or his best friend

    DesignPics Inc. via Newscom file

    The "how cute" reaction evoked by scenes such as the one shown here can quickly change to "ick" when our dogs start gnawing on their fur to rid themselves of fleas. The wingless, blood-sucking insects can also be more than an itchy nuisance: they are known to spread bubonic plague between rodents and humans, which has killed millions of people. Experts recommend frequent vacuuming, regular washing of pet bedding and treating household pets with topical insecticides.

  • Mosquitoes the icky and deadly

    Rothamsted Research

    For many of us, mosquitoes are more annoying than nasty; though most of us have uttered an ick or two when we successfully swat one on an exposed arm or leg only to create a skid mark of our own blood and bug. But more than ick, the insects are vectors of lethal disease. More than a million people each year die from malaria, a disease caused by parasites in red blood cells that is spread by mosquitoes in some parts of the world such as Africa. In an experiment with a twist, scientists attempting to develop a malaria vaccine recently successfully used mosquitoes to vaccinate humans against the disease.

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