spiders
"The next time you see a spider web, please, pause and look a little closer. You'll be seeing one of the most high-performance materials known to man."
- Cheryl Hayashi
- Cheryl Hayashi
introduction
Spiders, or organisms in the order Araneae, are air-breathing arthropods identified generally by their eight legs, fangs commonly able to inject venom, and spinnerets that create silk. Spiders, unlike insects, do not have antennae. Their bodies consist of two main body parts instead of the three typically seen in insects. The heads of spiders are fused to the thorax in a body part called a cephalothorax or prosoma. All eight of a spider's legs attach to the cephalothorax, and a thin, flexible waist (called a pedicel) attaches the cephalothorax to the abdomen, allowing it to move from side to side. Spider's abdomens are soft and can expand when filled with food or eggs. The abdomen contains the spider's circulatory and respiratory systems as well as reproductive organs and silk glands.
There are differences in body makeup between female and male spiders, some internal and some external. The most reliable way to tell the difference between a male and female is by looking at the reproductive parts. Female spiders will have an epigynum, which is a reproductive opening located on the underside of their abdomen near the front. Male spiders will not have this opening. A second difference is that male spiders have paired pedipalps (which look like tiny boxing gloves) used as secondary sex organs to deliver sperm, while those of females are used to probe and assist in prodding prey. Male spiders can be much smaller than their female counterparts, and can also be more colorful, but this is not always the case.
Female spiders have an opening on the underside of the front of abdomen.
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Male spiders have paired pedipalps that look a bit like boxing gloves.
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There is sometimes a large difference between the size of female and male spiders of the same species.
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Male spiders will sometimes be brightly colored.
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Spiders typically have eight eyes, each with a single lens, though the number of eyes varies by species from none to a dozen. This differs from insects, which have compound eyes. Some spiders have pretty good vision, and jumping spiders have eyes that even see in color. Most spiders, however, have poor eyesight. Instead, they sense more through vibrations in soil, webbing, or water.
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The bodies of spiders are filled with blue-tinted haemolymph, which contains a protein that functions similar to hemoglobin in humans. Their tubular hearts are located along the top of their abdomen, above their intestine. Female spiders have ovaries in their abdomens under intestines and above their silk glands and spinnerets. |
Spiders generally range in body length from 0.02 to 3.5 inches. The smallest spider in the world is from the genus Patu, which includes many pint-sized arachnids. It is the male Patu digua spider, native to Colombia, and reaches just 0.014 inches long. The largest spider in the world, by contrast, is the Goliath Birdeater (Theraphosa blondi). It is a type of tarantula, and is typically found in northern South America. This giant reaches up to 5.1 inches in body length (not including its legs).
Spider Behavior
Almost all known spider species are predators, mostly consuming insects or other spiders. A few species, however, can also feed on frogs, lizards, fish, birds, or bats. Spider's digestive systems are too small to process solids, and so they liquidize their meals using digestive enzymes to flood the internal systems of prey and grind them up with the bases of their pedipalps. Some spiders will supplement their diet from time to time with nectar, sap, or pollen, but most need a carnivorous diet to survive. There is an exception, however. The jumping spider species Bagheera kiplingi is typically herbivorous, feeding mainly on sugar produced by Acacia plants.
Spider diets consist mainly of insects.
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There are some spiders large enough to catch and consume bats.
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Some spiders will supplement their diet with pollen.
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The herbivorous Bagheera kiplingi.
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Once of the most recognizable spider behaviors is that they spin webs. All spiders spin silk, though only half of spider species make true webs. The other half of the group hunt for their prey or lay in wait for their next meal. Adult male spiders don't typically spin webs, though they can for the purposes of courtship of females and sperm induction. There are a few main varieties of webs that spiders will create, including:
Spiral orb webs.
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Tangle Webs or Cobwebs
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Funnel Webs
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Tubular Webs that run up trees or along the ground.
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Net-Casting Web
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Bolas spiders snag their prey with fisherman-like tactics.
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Spider Hunting Behavior
In addition to spinning a web to catch prey, spiders will also hunt for their next meal. Hunting on land is the preferred method of many spiders, including Jumping Spiders and Wolf Spiders. Some of these spiders have enhanced eyesight to assist them, and they are generally robust and agile hunters. There are some species of spider that will hunt on water, such as Dolomedes spiders. These critters wait at the edge of pools and slow-flowing streams, and anchor themselves to the shoreline with their rear legs. The rest of their body lies on the water, stretched out and waiting for prey. Once a vibration is felt, the spider runs across the surface of the water and subdues the prey. This is mainly done to hunt insects, but some larger spiders are also known to hunt small fish.
In addition to spinning a web to catch prey, spiders will also hunt for their next meal. Hunting on land is the preferred method of many spiders, including Jumping Spiders and Wolf Spiders. Some of these spiders have enhanced eyesight to assist them, and they are generally robust and agile hunters. There are some species of spider that will hunt on water, such as Dolomedes spiders. These critters wait at the edge of pools and slow-flowing streams, and anchor themselves to the shoreline with their rear legs. The rest of their body lies on the water, stretched out and waiting for prey. Once a vibration is felt, the spider runs across the surface of the water and subdues the prey. This is mainly done to hunt insects, but some larger spiders are also known to hunt small fish.
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An interesting case study is female water spiders (those in the species Argyroneta aquatica), which build underwater webs that they fill with air and use for digesting prey, molting, mating, and raising offspring. These spiders live most of their lives in their underwater biospheres. |
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Another spider hunting tactic is deception. Some spiders will mimic other animals so that their prey is lured into a false sense of security. For example, some spiders will pretend to get caught in another spiders' web, and when the other spider comes out to see what's for dinner, they pounce and digest the surprised web-owner. Some other spiders will manipulate UV signals to attract bees to flowers in which they are hiding.
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In contrast, trapdoor spiders construct terrestrial burrows with a camouflage door made of vegetation, soil, and silk. They lay in wait just inside this door and capture prey when it comes close enough. Another type of spider, the Kaira spider uses pheromone to attract moths and catches insects with a basket formed from its legs. |
Spider Reproduction
Spiders reproduce sexually, and male spiders will spin small sperm webs onto which they ejaculate, and then transfer the sperm to their palpal bulbs at the end of their pedipalps (the parts that look like mini boxing gloves). When males detect of a sign of a female nearby, he begins his courtship ritual. These techniques are used in the hopes that the female will not eat him after copulation. After insemination, males will commonly have parts of their pedipalp broken off inside of the female, plugging her hole and in doing so preventing other males from fertilizing. Rates of sexual cannibalism vary depending on the species of spider; it is higher in some species like Black Widows, which get their common name from the practice.
Spiders reproduce sexually, and male spiders will spin small sperm webs onto which they ejaculate, and then transfer the sperm to their palpal bulbs at the end of their pedipalps (the parts that look like mini boxing gloves). When males detect of a sign of a female nearby, he begins his courtship ritual. These techniques are used in the hopes that the female will not eat him after copulation. After insemination, males will commonly have parts of their pedipalp broken off inside of the female, plugging her hole and in doing so preventing other males from fertilizing. Rates of sexual cannibalism vary depending on the species of spider; it is higher in some species like Black Widows, which get their common name from the practice.
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Female spiders, once their eggs have been fertilized, will lay between 100 and 3,000 eggs in one or more silky egg sacs. In some species, females die after laying their eggs, and in others, females will lay their eggs in protective sacs attached to webs (or even carry them around). |
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Baby spiders will pass all larval stages inside the egg sac, and emerge as spiderlings. These offspring are very small and sexually immature, looking like miniature versions of adults. As they grow, they molt multiple times, and reach adulthood in a few weeks to a few years, depending on the species. Most spiders live for one or two years, though some have been documented to live up to 43 years.
spider Species
There are around 40,000 species of spiders worldwide, generally divided into six groups: Orb-Weaving Spiders, Wolf Spiders, Jumping Spiders, Tarantulas, Crab Spiders, and Trapdoor Spiders. The following list includes some of the spider species that are commonly found in California. If you are in another area, make sure to do some research on which spiders can be found around you.
Wolf Spider
Alopecosa kochi |
Johnny Cash Tarantula
Aphonopelma johnnycashi |
Orb Weaver
Araneus andrewsi |
Cross Orb-Weaver
Araneus diadematus |
Cat-Faced Spider
Araneus gemma |
Beach Wolf Spider
Arctosa littoralis |
Silver Garden Spider
Arglope argentata |
Black and Yellow Garden Spider
Arglope aurantia |
Banded Green Spider
Arglope trifasciata |
Red and White Steatoda
Asagena fulva |
Cobweb Spider
Asagena medialis |
Grey House Spider
Badumna longinqua |
California Trapdoor Spider
Bothriocyrtum californicum |
Hacklemesh Weaver
Callobius severus |
Ant-Mimic Spider
Castianeira athena |
Ant-Mimic Spider
Castianeira thalia |
Long-Legged Sac Spider
Cheiracanthium mildei |
Jumping Spider
Colonus hesperus |
Woodlouse Hunter
Dysdera crocata |
Orb Weaver
Eriophora edax |
Tropical Orb Weaver
Eriophora ravilla |
Western Parson Spider
Herpyllus propinquus |
Huntsman Spider
Heteropoda venatoria |
Ghost Spider
Hibana incursa |
Wolf Spider
Hogna antelucana |
Marbled Cellar Spider
Holocnemus pluchei |
American Sand Assassin
Homalonychus theologus |
Brown Widow Spider
Latrodectus geometricus |
Western Black Widow
Latrodectus hesperus |
Bolas Spider
Mastophora cornigera |
Gray Wall Jumper
Menemerus bivattatus |
Half Edged Wall-Jumping Spider
Menemerus semilimbatus |
Hacklemesh Weaver
Metaltella simoni |
Golden-Rod Crab Spider
Misumena vatia |
White-Banded Crab Spider
Misumenoides formosipes |
Arabesque Orb Weaver
Neoscona arabesca |
Hentx Orb-Weaver
Neoscona crucifera |
Western Spotted Orb Weaver
Neoscona oaxacensis |
Eared Dome Sheet-Web Weaver
Neriene digna |
Giant Crab Spider
Olios giganteus |
Common House Spider
Parasteatoda tepidariorum |
Lesser Green Lynx Spider
Peucetia longipalpis |
Jumping Spider
Phidippus adumbratus |
Bold Jumper
Phidippus audax |
Johnson Jumping Spider
Phidippus johnsoni |
Red Jumping Spider
Phidippus nikites |
Long-Bodied Cellar Spider (Daddy Long Legs)
Pholcus phalangioides |
Wafer-Lid Trapdoor Spider
Promyrmekiaphila clathrata |
Trash Line Spider
Reo eutypus |
Jumping Spider
Sassacus vitis |
Lanceolate Wolf Spider
Schizocosa maxima |
Table Grape Spider
Schizocosa mccooki |
Mouse Spider
Scotophaeus blackwalli |
Tube Web Spider
Segestria pacifica |
Common-Patterned Ant-Mimic Ground Spider
Sergiolus montanus |
False Black Widow
Steatoda grossa |
Noble False Widow
Steatoda nobilis |
Triangulate Cobweb Spider
Steatoda triangulosa |
Rural Funnel Web Spider
Tegenaria pagana |
Slender Crab Spider
Tibellus oblongus |
Table Grape Spider
Trachelas pacificus |
Cribellate Orbweaver
Uloborus diversus |
Garage Spider
Zoropsis spinimana |
Missing Sector Orb-Weaver
Zygiella x-notata |
Spiders in the garden
Spiders are beneficials in any garden or natural ecosystem, their main contribution being controlling insect populations. They are the most important terrestrial predators of pest insects and other small arthropods each year, and are willing to eat almost anything they can catch. In homes, spiders also prey on insects and other small creatures and rarely have human contact. It is a fact that many of the bites we blame on spiders are actually perpetrated by other insects. Spiders very rarely bite humans, and when they do, it's usually in self-defense because they are being squished or threatened.
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Even when a bite does happen, either from incidental contact or by foolishly slapping a spider while it is crawling on a body part, the majority of spiders are not toxic to humans. Spiders prey on very small insects, and their venom is not geared towards large animals. About 0.03% of spider species can cause physical harm to humans.
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Spiders are best left to their own devices; if there is a spider that is causing issues in the garden, it is most likely that it is making webs that are then walked through by garden visitors. Spiders take up residence beneath leaves and bark, in mulch or soil crevices, in wood, rock, and compost piles, and will also build webs near outdoor light fixtures and in open areas near homes where other insects try to enter. If spiders are found in the home, there isn't really a control method to use, they are simply just relocated to an outdoor area.
All over the world, biologists are noting a decline in the amount of individual spiders they see when out in the field. Unfortunately, there is no hard data available to use to document this trend, and it is mostly because spiders are not what people want to be spending their research money on. Scientists who study spiders, arachnologists, have a very hard time finding the funds necessary to even approach spider protection efforts. The first line of defense for spiders really is individuals lessening their negative reactions to them.
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The case for why people should care about spiders is strong. To begin with, the vast majority of spiders are harmless to humans. They are also excellent natural pest controls with voracious appetites for insects including mosquitoes, cockroaches, and aphids. In addition to consuming pests, they are an important food source for birds, fish, lizards, and small mammals. |
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Spiders are beneficial outside of their natural habitats, as well. Compounds in spider venom are being studied for their pharmaceutical and pest control applications, and medical and engineering research is being done on their incredibly strong silk. Unfortunately, none of these great reasons to love these little critters is likely to sway those with arachnophobia. Thankfully, citizen science may hold the key to both saving the spiders and making them more acceptable neighbors. There has been success in the past with citizen science projects, including the Great Backyard Bird Count and apps like iNaturalist. Projects like these have the potential to familiarize the general public with critters that are typically feared.
