Jumping spiders have such good eyes that they will usually watch any human who tries to watch them. Some species are very shy and will run away if the human gets too close. But some species, such as Phidippus audax (the audacious or brave jumping spider) and Platycryptus undatus, can become calm if the human comes close to them slowly. Sometimes they will jump onto one of your fingers and then jump from finger to finger and from hand to hand. They seem to want to explore.
Some jumping spiders of the genus "Portia" hunt other spiders in ways that seem intelligent, outflanking their victims or luring them from their webs. Laboratory studies show that "Portia"'s instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species. However, they seem to be relatively slow thinkers, which is not surprising as their brains are vastly smaller than those of mammalian predators.
Ant-mimicking spiders face several challenges: they generally develop slimmer abdomens and false "waists" to mimic the three distinct regions (tagmata) of an ant's body; they wave the first pair of legs in form to their heads to mimic antennae, which spiders lack, and to conceal the fact that they have eight legs rather than six. They have large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective hairs to resemble the shiny bodies of ants. In some spider species males and females mimic different ant species, as female spiders are usually much larger than males.
Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant, for example many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus "Synemosyna" walk on the outer edges of leaves in the same way as "Pseudomyrmex". Ant-mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However several ant-mimicking spiders prey either on ants or on the ants "livestock" such as aphids. When at rest the ant-mimicking crab spider "Amyciaea" does not closely resemble "Oecophylla", but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.
Spiders reproduce sexually and fertilization is internal but indirect. In other words, the sperm is not inserted into the female's body by the male's genitals but by an intermediate stage. Unlike many land-living arthropods, male spiders do not produce ready-made spermatophores (packages of sperm). Instead, they spin small sperm webs on to which they ejaculate and then transfer the sperm to structures on the tips of their pedipalps. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or 'safety ropes', the male can identify the species and sex of these objects by smell.
Spiders generally use elaborate courtship rituals to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In some species males mate with newly molted females, which are too weak to be dangerous to the males.
In web-weaving species precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female's body are important in many spiders that hunt actively, and may 'hypnotize' the female. Gestures and dances by the male are important for jumping spiders, which have excellent eyesight. If courtship is successful, the male injects his sperm from the pedipalps into the female's genital opening on the underside of her abdomen. Female reproductive tracts vary. Some are simple tubes, but others have chambers where females store sperm, and release it when they are ready.
Males do get eaten in some species. Males of the genus "Tidarren" cut off one of their palps, and enter adult life with one palp only. The palps are 20% of male's body mass in this species, and detaching one of the two improves mobility. In the Yemeni species "Tidarren argo", the remaining palp is then torn off by the female. The separated palp remains attached to the female's opening for about four hours. In the meantime, the female feeds on the palpless male. In over 60% of cases the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female's genital opening; in fact the males co-operate by trying to impale themselves on the females' fangs. Observation shows that most male redbacks never get an opportunity to mate, and the 'lucky' ones increase the likely number of offspring by ensuring that the females are well-fed. However males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates' webs.
Females lay up to 3,000 eggs in one or more silk egg sacs, which maintain a fairly constant humidity level. In some species the females die afterwards, but females of other species protect the sacs by attaching them to their webs, hiding them in nests, carrying them in the chelicerae or attaching them to the spinnerets and dragging them along.
Baby spiders pass all their larval stages inside the egg and hatch as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a wolf spider's brood cling to rough bristles on the mother's back, and females of some species respond to the "begging" behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitate food.
Like other arthropods, spiders have to moult to grow as their cuticle ("skin") cannot stretch. Most spiders live for only one to two years, although some tarantulas can live in captivity for over 20 years.
Of the 40,000 spiders, less than 12 are known to be dangerous to humans. Most of the time, being bitten by a spider is painful. Most spiders use venom to paralyse their prey; they kill it through eating, or through a bite. A few spiders have venoms that can be dangerous to weakened people and those allergic to it. Since 1927, 13 people have died, after a bite from a "Atrax robustus" spider from Australia.
The spider that kills the most people, the black widow and other spiders in the genus "Latrodectus" are around 1 cm. in body length. The "Atrax" and "Phoneutria" spiders, which are also capable of killing people, both average around 2.5 cm. or one inch, and even the Widow spiders are large enough to be easily noticed.
Even relatively small spiders like "Phidippus audax" can give a painful bite if you hurt them, but spiders are very helpful to human beings because they control insects that eat our crops.
Being afraid of spiders is a very common phobia (fear). The widow spiders (black widows and other members of their genus) never willingly leave their webs, so usually people get bitten when they touch the spider by mistake.
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1760s
Grass
Grass is a plant with narrow leaves growing from the base. A common kind of grass is used to cover the ground in a lawn and other places. Grass gets water from the roots in the ground. Grasses are monocotyledon plant, herbaceous plants.
The grasses include the "grass", of the family Poaceae (also called Gramineae), as well as the sedges (Cyperaceae) and the rushes (Juncaceae). These three families are not closely related but belong to different clades in the order Poales.