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

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.
Male spiders have paired pedipalps that look a bit like boxing gloves.
There is sometimes a large difference between the size of female and male spiders of the same species.
Male spiders will sometimes be brightly colored.
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. 

​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.
There are some spiders large enough to catch and consume bats.
Some spiders will supplement their diet with pollen.
The herbivorous Bagheera kiplingi.
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.
Tangle Webs or Cobwebs
Funnel Webs
Tubular Webs that run up trees or along the ground.
Net-Casting Web
Bolas spiders snag their prey with fisherman-like tactics.
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.

​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.
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.

​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.

​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). 
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.
Alopecosa kochi
(Wolf Spider)
Found in Canada, Mexico, and the United States.
Aphonopelma johnnycashi
(Johnny Cash Tarantula)
Named for Johnny Cash due to its discovery near Folsom Prison, CA. Up to 6 inches long. Females are dark brown, males are black.
Araneus andrewsi
(Orb Weaver)
These spiders are found in the United States.
​Araneus diadematus
(Cross Orb-Weaver)
Native to Europe and introduced to North America. Females up to 0.8 in. and yellow to dark grey. Males smaller and orange-brown.
​Araneus gemma
(Cat-Faced Spider)
Found in the western U.S. and Canada, this common spider is harmless to humans.
​Arctosa littoralis
(Beach Wolf Spider)
Found in North and Central America.
Argiope argentata
(Silver Garden Spider)
Native to the Americas and the Caribbean, this species forms webs with an 'X' shape in the middle. 
Argiope aurantia
(Black and Yellow Garden Spider)
These spiders are typically striped with yellow, orange, and black. Native to the Americas.
​Argiope trifasciata
(Banded Green Spider)
​​In this species, females and much smaller males form webs close to each other. Native to North and South America.
Asagena fulva
(Red and White Steatoda)
Found in the United States and Mexico; these spiders are small, typically red-brown, and form cobwebs.
​Asagena medialis
(Cobweb Spider)
This species is native to the United States and Mexico. They are brown with light yellow to white markings on their abdomen. 
Badumna longinqua
(Grey House Spider)
Native to eastern Australia, this spider now has a worldwide distribution. ​0.43-0.59 inches long, dark grey-brown body, purplish legs.
​Bothriocyrtum californicum
(California Trapdoor Spider)
Brown spiders with darker legs; males smaller than females.
Callobius severus
(Hacklemesh Weaver)
Found in U.S. and Canada, 3/4" long. Red to brown with grey abdomen. Woodland species.
Castianeira athena
(Ant-Mimic Spider)
Found in the United States and Mexico.
Castianeira thalia
(Ant-Mimic Spider)
Found in the United States.
​Cheiracanthium mildei
(Long-Legged Sac Spider)
Pale green to tan bodied spiders with tan legs. To 0.4 inches long.
​Colonus hesperus
(Jumping Spider)
Native to the southwestern U.S. and Mexico, peaks in population in May.
​Dysdera crocata
(Woodlouse Hunter)
Between 0.4 and 0.6 inches long, with tawny to dark orange and yellow-brown bodies.
​Eriophora edax
(Orb Weaver)
This species has a range from the U.S. through Brazil.
Eriophora ravilla
(Tropical Orb Weaver)
Found in a range from the U.S. to Brazil.
Herpyllus propinquus
(Western Parson Spider)
These ground spiders are found in North America.
​Heteropoda venatoria
(Huntsman Spider)
Native to tropical regions, these spiders have flat, brown bodies to between 1 and 4 inches long.
​Hibana incursa
(Ghost Spider)
Found in the U.S. and Panama, this species...
Hogna antelucana
(Wolf Spider)
Found in the United States, this spider...
Holocnemus pluchei
(Marbled Cellar Spider)
These common household spiders have a wide range, and like to join existing webs.
Homalonychus theologus
(American Sand Assassin)
These camouflaged spiders are found in desert landscapes under rocks or in dead cacti.
​Latrodectus geometricus
(Brown Widow Spider)
With black and white patters on the abdomen and an orange-yellow hourglass, these spiders reach 1 to 1.5 inhes long.
Latrodectus hesperus
(Western Black Widow)
Females are black with a red hourglass shape, males are smaller and brown. Native to western North America.
​Mastophora cornigera
(Bolas Spider)
Native to the U.S. through Nicaragua.
​Menemerus bivittatus
(Gray Wall Jumper)
These spiders have a widespread range, and are up to 0.35 inches long.
Menemerus semilimbatus
(Half Edged Wall-Jumping Spider)
To 0.33 inches long, covered with short grey hairs with light brown legs that have dark rings and patches.
​Metaltella simoni
(Hacklemesh Weaver)
Native to South America, and now introduced to the U.S. and Canada. Brown with darker parts.
​Misumena vatia
(Golden-Rod Crab Spider)
Wide, flat body that is short and crab-like. These spiders can walk sideways. Spiders are yellow and white.
Misumenoides formosipes
(White-Banded Crab Spider)
These sit-and-wait predators are white with red markings, and males are orange and red.
​Neoscona arabesca
(Arabesque Orb Weaver)
Common in fields, forests, and gardens. To .25 inches. Females grey with brown, males brown.
​Neoscona crucifera
(​Hentx Orb-Weaver)
Found in the United States, this species reaches up to 0.75 inches. Light grey/brown bodies and banded legs. 
​Neoscona oaxacensis
(Western Spotted Orb Weaver)
Native to the Americas, these large spiders reach up to 0.7 inches long (males to 0.5 in.). Grey-black with lighter markings and banded legs.
​Neriene digna
(Eared Dome Sheet-Web Weaver)
Found in the US and Canada.
​Olios giganteus
(Giant Crab Spider)
Found in the US and Mexico; black, brown/tan and orange bodies.
Parasteatoda tepidariorum
(American House Spider)
These spiders live near or in human dwellings, and range in color from tan to black.
​Peucetia longipalpis
(Lesser Green Lynx Spider)
Found in an area that ranges from the US down through Venezuela.
Phidippus adumbratus
(Jumping Spider)
From US and Mexico, with a hazy dark pattern on its body and a reddish abdomen.
​Phidippus audax
(Bold Jumper)
Black to grey with banded legs, often with bright markings.
​Phidippus johnsoni
(Johnson Jumping Spider)
About 0.4 inches long. Black body and legs with red abdomen.
Phidippus nikites
(Red Jumping Spider)
Native to the US and Mexico.
​Pholcus phalangioides
(Long-Bodied Cellar Spider)
With legs 5-6 times the length of their brown bodies. To 0.3 in.
Promyrmekiaphila clathrata
(Wafer-Lid Trapdoor Spider)
This species is native to California, and has a dusky, brownish-grey body. Burrows in soil with a silky door.
​Reo eutypus
(Trash Line Spider)
Found in the US.
Sassacus vitis
(Jumping Spider)
Native to North America. Females are much larger than males, and are more brown than black.
Schizocosa maxima
(Lanceolate Wolf Spider)
To 1.1 inches long, native to California and Oregon. Body is brown-grey.
Schizocosa mccooki
(Table Grape Spider)
Native to North Amrieca, these spiders reach 0.9 inches long and are grey-brown.
​Scotophaeus blackwalli
(Mouse Spider)
These ground spiders do not build webs, and hunt nocturnally. They are shiny and dark brown-silver.
​Segestria pacifica
(Tube Web Spider)
From the western areas of North America, brown to dark brown with abdomen mottling.
Sergiolus montanus
(Common-Patterned Ant-Mimic Ground Spider)
​Found in North America.
Steatoda grossa
(False Black Widow)
Found in many areas of the globe, to 0.4 in. long. Typically mahogany-brown.
​Steatoda nobilis
(Noble False Widow)
Brown spiders with reddish-orange legs. To 0.5 inches long.
Steatoda triangulosa
(Triangulate Cobweb Spider)
To 1/4 in. long with brown bodies and yellow-brown legs. Purple-brown zig-zag pattern created with lighter areas on their abdomen.
​Tegenaria pagana
(Rural Funnel Web Spider)
Brown spiders with some lighter markings, grey abdomen. To 0.45 inches long.
​Tibellus oblongus
(Slender Crab Spider)
These light yellow spiders with brown stripes do not spin webs.
Trachelas pacificus
(Table Grape Spider)
Found in the US and Mexico.
Uloborus diversus
(Cribellate Orbweaver)
This desert spider is native to the SW US and Mexico.
Zoropsis spinimana
(Garage Spider)
Brown spiders with dark markings. Males to 0.5 in. and females to 0.7 inches long.
Zygiella x-notata
(Missing Sector Orb-Weaver)
Females have leaf-like markings and all are brown-tan. Primarily stick close to human populations.

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.

​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.
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 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.

​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. 
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.

Video

Learn how spiders came to be on this planet.
Learn about some of the more endearing qualities that spiders possess.
All you need to know about the classification and physical makeup of spiders.
Learn about the common spiders in your yard through this channel, starting with the Goldenrod Crab Spider.

Resources & References

Everyone Should Start Counting Spiders
Wikipedia: Spider
Spiders - Agricultural Biology
Fear of Spiders may have its Evolutionary Roots in Aversion to Scorpions