Most arachnids are harmless and contribute to the give and take of nature by controlling the populations of the insects they prey on or the plants, reptiles, birds, or mammals that serve as their hosts. A few species are serious agricultural pests. The bites of some spiders, such as the black widow spider and the brown recluse spider, and the stings of a few species of scorpions are dangerously poisonous to humans.
1. Phrynus parvulus; 2. Striped scorpion (Centruroides vittatus); 3. Demodicid (Demodox folliculorum); 4. Rocky Mountain wood tick (Dermacen-tor andersoni); 5. Ricinoides afzelii; 6. Book scorpion (Chelifer cancroides); 7. Giant whip scorpion (Mastigoproctus giganteus); 8. Emperor scorpion (Pandinus imperator). (Illustration by Bruce Worden)
1. Cellar spider (Pholcus phalangioides); 2. Egyptian giant solpugid (Galeodes arabs); 3. Zebra spider (Salticus scenicus); 4. Agastoschizomus lucifer; 5. Eukoenenia draco; 6. Atypus affinis; 7. Spruce-fir moss spider (Microhexura montivaga); 8. Harvestman (Phalangium opilio). (Illustration by Bruce Worden)
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