Spiders are a diverse group and are the primary arthropod predators that naturally regulate many insect pests. The two-part spider shape is well known. Its head and thorax are combined to make the cephalothorax. Four legs are attached to each side of the cephalothorax. Spider eyes are in front - some have very large eyes. Like all arachnids, spiders have no antennae or wings and they have 8 legs - insects have 6. They consume up to 2 times their own body weight daily. They live everywhere - some species have been kept alive for over two years without feeding. Population densities of spiders are estimated to range from 27,170 to 5.4 million/ha for some habitats (Bristowe, 1958; Gertsch, 1979). |
While all spiders are poisonous to some extent, very few bite humans. Spider mouthparts, located in front below the eyes, have two short needle-tipped appendages, called chelicerae. These needles, or central fangs, are connected internally to poison sacs. The fangs are used to bite prey (mostly other arthropods) and inject poison to immobilize it. Two short leg-like mouthparts help hold their paralyzed prey, while the chelicerae work back and forth tearing the exoskeleton. As blood wells out, it is sucked into the mouth cavity and ingested. Spiders keep working their prey in this way until all the juices are gone and the remainder is a dry crumbled lump. The abdomen is located behind the cephalothorax; it is sac-like, usually globular.
The anal opening is located near the end of the abdomen and close by are some short appendages called the spinnerets. Silk webbing threads out from these spinnerets. Spider silk has great elasticity and can stretch 1/5 of its length without breaking. The silk is protein and is digested by enzyme cleaners that contain protease enzymes. All spiders produce silk, and they use silk in more interesting ways than most other silk producers. Spiders make silk retreats such as tubes and funnels, they make irregular cobwebs as well as the evenly spaced, spiraled great orb webs. Most spiders feed out a dragline wherever they walk and never fall off edges without catching themselves. While spiders don't have wings, they "fly"; nonetheless, by releasing a thread of silk until it is long enough for the wind to catch it and carry them off — the process is known as ballooning. Newly-hatched spiderlings use this method to leave the hatching area. Most species are nocturnal, unobtrusive - often pretending to be dead when molested - most spiders in homes are usually found in undisturbed, dark or dimly lit, cool, damp places - these areas are where people are most likely to be bitten when they "bug", accidentally imprison, or crush these beneficial hunters.
Basically only two spiders are considered dangerous to humans in the United States: the Black Widow and the Brown Recluse. In reality, these two names each represent several different species. Spiders are only distantly related to insects. Unlike insects, they have 4 pairs of legs but lack wings and antennae. Most spiders can be kept out of buildings by tight screens, weather-stripping and caulking. Keep screens and other openings in good repair. Caulk all seams around windows and doors. Indoors: Remove by vacuuming. All spiders are predators feeding primarily on insects and other arthropods but they can survive for very long periods without food. The average spider eats 100 bugs per year. You are never more than 12' from a spider.
Ballooning spiderlings can ascend over 15,000' and have been sighted landing on ships sailing the mid-Pacific. Silk starts as a liquid protein which becomes a solid thread. An orb web may have 1,200 junctions, each crafted perfectly. The spider must calculate the exact length and tension of each succeeding line so the earlier ones don't go slack. Slack lines don't transmit vibrations. The standard orb web is completed in only 20 minutes at about 3 - 4 a.m. Most orb weavers rebuild their webs once a day; they take the web down and eat it to be completely recycled in their body and reused in about 30 minutes. Spiders coat their feet with an oily fluid from their mouths so they don't stick to the webs. Spiders can replace lost legs.
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