Many
spiders hunt by building webs to trap insects. These webs
are made of spider silk, a thin, strong protein strand
extruded by the spider from spinnerets on the end of the
abdomen. All spiders produce silk, although not all use
it to spin elaborate traps. Silk can be used to aid in
climbing, forming smooth walls for burrows, cocooning
prey, and for many other applications. New World tarantulas
have a patch of urticating hairs on their abdomens, while
these are lacking in Old World species. Spiders have eight
legs compared to the insects' six, and their eyes (usually
eight) are single lenses rather than compound eyes like
those of most insects.
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