#arachnida

Araneae is the largest order of arachnids and ranks 7th in total species diversity among all orders of organisms

Spiders tend to get a bad rap (mostly due to western media banking on arachnophobia and spreading misinformation) but they are incredibly beneficial to humans, eating many of the species we consider pests. Some crops, such as cranberries, tomatoes, and potatoes, rely on spiders for pest control. It has been found that wherever farmers release spiders, their crop yields increase, while also cutting down on the use of chemical pesticides by 80%.

There are around 50,000 species of spider and all but one family (Uloboridae) is venomous. However, this venom is mainly used to capture prey, and only 10 genera have venom considered medically significant to humans. Bites are rarer than the media would have you think (if you woke up with a random mark on you and did not see the culprit, no, that probably was not a spider bite…), and deaths are even more rare, as they are usually a result of secondary infections, allergic reaction, or pre-existing conditions. You are more likely to die from a mosquito bite!

The jumping spider Bagheera kiplingi is notable as the only known mainly herbivorous spider. It feeds on specialized protein- and fat-rich nubs on the leaves of the acacia trees (genus Vachellia) it lives in. The spider must actively avoid the ants that guard these trees against intruders, as they compete for the food source. Although the nubs account for over 90% of B. kiplingi’s diet, the spiders also consume nectar and occasionally steals ant larvae from passing worker ants for food. Sometimes, they may also cannibalize other B. kiplingi spiders in times of desperation, especially during the dry season. Despite their occasional acts of predation, the spiders' tissues have been found to exhibit isotopic signatures typical of herbivorous animals, implying that most of their food comes from plants, a first for spiders, though many other spider species will also supplement their diet with nectar, other sugary substances, and pollen.

Studies on jumping spiders of the genus Portia have demonstrated that these spiders display intelligent hunting behaviour, which suggests that they are capable of learning and problem solving, traits normally attributed to much larger animals. Portia spiders are known to improvise via trial and error and then remember their new approach, exhibit spatial memory and object permanence, plan ahead, make detours, and accomplish tactical problems that can take up to an hour, all with a brain significantly smaller than the size of the head of a pin with less than 100,000 neurons (a mouse brain has about 70 million neurons, and a human about 86 billion). Portias can also distinguish their own draglines (webbing) from others, and discriminate between known and unknown spiders, displaying social intelligence as well. Members of the species Portia africana have been observed living together and sharing prey, and mature Portia males will often cohabitate with subadult females.

The visual acuity of some jumping spiders exceeds by a factor of ten that of dragonflies (which have by far the best vision among insects)

Net-casting Spiders (family Deinopidae) catch prey by stretching a web across their front legs and launching forward when prey comes near. Their main eyes are very large, and have excellent night vision, allowing them to cast their nets effectively on nocturnal prey such as moths. Their eyes are able to gather available light more efficiently than the eyes of cats and owls, and are able to do this despite the lack of a reflective layer (tapetum lucidum). Instead, each night, a large area of light-sensitive membrane is rebuilt within the eyes, and since arachnid eyes do not have irises, this membrane is rapidly destroyed again at dawn.

The smallest species of spider is Patu digua from Colombia. Males reach a body size of only about 0.37 mm (0.015 in), roughly one fifth the size of the head of a pin.

The Hawaiian Happy-face Spider (Theridion grallator) is known for having a wide range of color morphs, all affected by its diet. For example, if the spider ingests certain species of flies and butterflies, it will turn orange. But if it eats a lot of Hemipterans (“true bugs”) and caterpillars, it will turn green. Meanwhile, the Goldenrod Crab Spider (Misumena vatia), an ambush hunter which lives on flowers, can change its color through the molting process, based on the flower it chooses to hide on.

The Diving Bell Spider (Argyroneta aquatica) is the only known fully aquatic spider, though several other spiders are semi-aquatic, either periodically living underwater or being willing to dive. But the Diving Bell Spider lives its entire life underwater, only briefly surfacing to replenish its oxygen supply and occasionally bringing prey to the surface to feed. The Diving Bell Spider breaths air, but traps an air bubble around itself within a dense layer of hydrophobic hairs on its abdomen and legs, allowing it to breathe underwater. It builds a waterproof, silk-based nest underwater that further traps air, similar to a diving bell, which gives it its name. Females build a larger bell, because they will also use the nest to raise their young. The spider must regularly replenish the bell with oxygen.

The Wheel Spider (Carparachne aureoflava) of the Namibian desert escapes parasitic wasps by flipping onto its side and cartwheeling down sand dunes.

Some species of spider are highly social, weaving webs together and sharing prey. One of the best known and studied is Anelosimus eximius, whose colonies can number in the thousands. In these colonies, web maintenance seems to fall on females and juveniles, while adult males do not take part. Eggs and young and cared for communally, and young are fed via regurgitation (like baby birds). Smaller prey is ignored and usually allowed to escape, while larger prey such as wasps, bees, beetles, butterflies, true bugs, cockroaches, and grasshoppers are taken down by a group of 30-50 spiders, after which the whole colony may feed on the prey.

“Arachnida” comes from a story told by the Roman poet Ovid in his poem Metamorphoses, in which Arachne was a Lydian girl who challenged the goddess Minerva to a weaving contest. Arachne won, enraging Minerva, causing Arachne to hang herself out of shame, reincarnating as the first spider. The myth both provided an etiology of spiders' natural web-spinning talent and was a cautionary tale about hubris.

One of the most well-known figures from the folklore of the Akan people of southern Ghana is Anansi or Ananse, a trickster-spirit associated with stories, wisdom, knowledge, wit, and cunning, and most commonly depicted as a spider or a spider-like man.

In Anishinaabe culture, dreamcatchers are meant to represent spiderwebs and are used as a protective charm for infants. They originate from the Spider Grandmother, who takes care of the children and the people of the land in many Native American cultures.