any of about 38,000 species of arachnids that differ from the insects in having eight legs rather than six and in having the body divided into two parts rather than three. The use of silk is highly developed among spiders. Spider behaviour and appearance are diverse, and the araneids outside Europe, Japan, and North America have not...
any member of the arthropod group that includes spiders, daddy longlegs, scorpions, and (in the subclass Acari) the mites and ticks, as well as lesser-known subgroups. Only a few species are of economic importance—for example, the mites and ticks, which transmit diseases to humans, other animals, and plants.
...prey to the young after they emerge from the burrow. The female whip scorpion attaches eggs to herself and carries them until the young go through several molts; she dies as soon as they leave. Spiders generally weave a silken case for eggs and young. The female wolf spider carries her young on her back. Some young spiders build a family or community web together. The harvestmen and mites...
...abdomen (12 somites); prosoma has 6 pairs of appendages, 4 pairs used for walking, last 2 pairs lost in some mites; instinctive behaviour highly developed. Order Araneida or Araneae (spiders)38,000 species found nearly worldwide. Size 0.05–9.0 cm; chelicerae 2-jointed, with ducts for poison glands;...
The legs of spiders are unusual because they lack extensor muscles and because blood is used as hydraulic fluid to extend the legs in opposition to flexor muscles. The blood pressure of a resting spider is equal to that of a human being and may double during activity. The high pressure is maintained by valves in the anterior aorta and represents an exception to the general rule that open...
Whether spiders have a sense of hearing has long been debated. Early anecdotal observations concerning this matter have now been reinforced with both behavioral and electrophysiological evidence showing without doubt that spiders are sensitive to mechanical vibrations and also to aerial sounds. Whether this sensitivity should be regarded as hearing is considered later in this section, after a...
Some male spiders perform elaborate courtship actions that affect selectively females that are ready to respond sexually. The male, in testing for a receptive female, first stands out of reach and goes through elaborate precise gestures with limbs, pedipalps, and other body parts that are distinctively shaped or patterned in a manner characteristic of the species. Perhaps even more remarkable...
...as in many birds, the females resort to displays that resemble the food-begging behaviour normally seen in the young. Males frequently respond to this display by actually regurgitating food. Male spiders of some species offer the larger and more aggressive females food as bait, and copulation occurs while the female is eating the food rather than her potential mate. Mutual feeding displays,...
The arachnids (e.g., spiders and scorpions) exhibit the earliest pattern of classical courtship behaviour during which rather ritualized movements are involved. In the true scorpions this behaviour takes the form of the promenade à deux, in which the male holds the female by her front claws and apparently stings her in a joint near the base of the claw. The ensuing...
Among arthropods, ocelli are the main organs of sight in arachnids such as spiders and in insect larvae that undergo complete metamorphosis (i.e., a radical physical change during development). Insects that undergo incomplete metamorphosis have three ocelli arranged in a triangle on the dorsal, or top, part of the head; these are subsidiary, however, to the main organs of sight, the...
...duct, contributes to the semen (fluid containing sperm) or participates in spermatophore formation. The ninth body segment and sometimes the tenth bear appendages for sperm transfer. Scorpions and spiders have tubular or saclike gonads; the female system is equipped to receive and store sperm, and, in some species, the female retains the eggs long after fertilization has occurred. Male spiders...
Among some spiders the male's pedipalp, a grasping or crushing appendage, contains a bulb and an extensible, coiled structure (embolus). As mating begins, the male dips the pedipalp into semen from his gonopore. The embolus is then placed in the female gonopore, and the sperm are transferred to her seminal receptacle. The female deposits the sperm along with her eggs into a silken cocoon, which...
The respiratory structures of spiders consist of peculiar “book lungs,” leaflike plates over which air circulates through slits on the abdomen. The book lungs contain blood vessels that bring the blood into close contact with the surface exposed to the air and where gas exchange between blood and air occurs. In addition to these structures, there may also be abdominal spiracles and...
By: Wood, Allison. Crain's Cleveland Business, 8/29/2005, Vol. 26 Issue 35, p18-18 The article reports that Todd Blackledge, an entomologist who studies arachnids at the University of Akron, is examining how the web constructions of black widows are affected by food availability. His hope is to see how external forces such as availability of prey affect their webs and the silk they produce to construct them. Synthesizing spider silk will be necessary for widespread use because creating spider farms for mass production is impractical. Blackledge is studying how the spiders produce silk used to construct webs and for other necessary functions such as wrapping prey. Reading Level (Lexile): 1180;
By: Milius, Susan. Science News, 8/26/2006, Vol. 170 Issue 9, p133-133 The article discusses the mating habits of the Australian redback spider. Animal behavior researcher Daniela Baggio discovered that male redback spiders often bite through the exoskeletons which protect the reproductive tracts of juvenile females in order to mate. The practice not only spares the life of the male spider, who is often eaten by larger adult females, but also results in the fathering of the majority of the juvenile female's offspring. Reading Level (Lexile): 1200;
By: Milius, Susan. Science News, 2/10/2007, Vol. 171 Issue 6, p94-94 The article reports on the courtship and mating patterns of Cosmophasis umbratica, a small jumping spider indigenous to tropical areas in southeast Asia. The male has areas that reflect ultraviolet light and the female responds by fluorescing. In the absence of ultraviolet light, the spiders show no interest in each other. Reading Level (Lexile): 1180;
By: Milius, S.. Science News, 4/24/2004, Vol. 165 Issue 17, p269-269 Discusses research being done on the sex organ removal practice of male spiders. Reference to study by Margarita Ramos and colleagues, published on the April 6, 2004 issue of "Proceedings of the National Academy of Sciences"; Size of a male spider's pedipalp; Process involved in the removal of a spider's sex organ; Potential benefit of the practice. Reading Level (Lexile): 1460;
By: Milius, Susan. Science News, 7/3/2004, Vol. 166 Issue 1, p14-14 The article reports that some jumping spiders, famed for eye-catching ornamentation and courtship dancing, have recently been recognized as accomplished vibration artists as well. New tests show that among Habronattus dossenus, a male's display-even if it's visually striking-probably won't succeed unless he sends the right seismic messages. Jumping spiders have large eyes, which give them the look of "surprised teddy bears," says Damian Elias of Cornell University. Their bodies sport colored patterns and hair tufts, which a courting male shows off as he waves and flicks his legs during his slow approach to a female. When a male has edged to within about a body length of the female, he starts thumping, scraping, and buzzing. The vibrations synchronize with the motions of the male's raised legs, almost as if he's snapping castanets over his head. Reading Level (Lexile): 1240;
By: Peterson, Karyn M.. Instructor, Oct2004, Vol. 114 Issue 3, p72-73 Presents a quiz for school children regarding spiders. Reading Level (Lexile): 630;
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