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Araneus diadematus

By Veronica Godines

Geographic Range

The range of the Araneus diadematus extends from New England and adjacent Canada across the northern states to Washington, Oregon, and British Columbia. (Kaston, 1972)

Habitat

Araneus diadematus lives in grasslands and requires some form of moisture. The environment must provide plenty of attachment sites for the scaffolding of the web and there must be sufficient vertical open space for the orb web. (Wise, 1993)

Physical Description

Female Araneus diadematus have lengths of 6.5 to 20 mm, whereas males are 5.5 to 13 mm. Color ranges from pale yellow brown to nearly black. The folium is not as distinct as some other Araneus species and includes a number of white or yellow spots. The largest spots are arranged longitudinally near the anterior end. Usually there is a pair of white spots at right angles to the longitudinal ones, which gives the group the form of a cross. The cross arrangement is more apparent in darker individuals and is caused by guanine cells which shine through the transparent cuticle. The carapace has a median and marginal dark bands. There are four pairs of legs which fan out radially from the connecting carapace and sternum. Each leg has seven segments: a coxa and a trochanter, which are both short; a long femur and a kneelike patella; a slender tibia and metatarsus; and finally a tarsus with three claws. The first pair of legs are relatively long and used as feelers for probing the environment. Sensory hairs densely cover the distal leg segments. The external sex organs of males and females are observed ventrally. Both male and female genital openings lie inside the epigastric furrow, except that the epigynum is situated in front of the female furrow. Males also have a bulb or palp used for the storage of sperm. (Foelix, 1982; Kaston, 1972)

  • Sexual Dimorphism
  • sexes shaped differently
  • Range length
    6.5 to 20 mm
    0.26 to 0.79 in

Reproduction

The internal reproductive organs of Araneus diadematus resemble those of other arthropods. Females have paired ovaries that lie in the abdomen and join to form a common oviduct which ends in the uterus and opens to the outside in the epigastric furrow. Females also have a pair of spermathacae or seminal receptacles where sperm taken in during copulation is stored until egg-laying. In males, a common duct is formed by a pair of coiled testes in the abdomen and opens to the exterior at the centre of the epigastric furrow. Males exude sperm through the epigastric furrow onto a sperm web and transfer it to their palps. The terminal palp is the sperm reservoir and carries out insemination through a narrow tube known as the embolus. The palp serves as a pipette which can suck up and release seminal fluid. Blood pressure within male palps increases so that sclerotized projections such as hooks and spines elevate into position to grasp on to the surface of the epigyne. Only the correct palp will fit into the appropriate epigyne. This ensures successful mating only between individuals of the same species. Males search for a female and are rather cautious when approaching a female, because they risk being considered prey. Males embrace the female's abdomen during copulation and insert one palp. Afterwards, the male leaves and his palps are refilled with sperm. This process may only be repeated a few times since the life expectancy of males is shorter than females. (Dewey, 1993; Foelix, 1982; Preston-Mafham and Preston-Mafham, 1996)

Females breed once, dieing shortly after laying their eggs. Individuals of this species breed at the end of the warm season, with young hatching in the following spring. (Dewey, 1993; Foelix, 1982; Preston-Mafham and Preston-Mafham, 1996)

Before the female starts making her egg sac, she withdraws for several days. She then spins a thin layer of single, tightly-woven silk threads. The first layer is molded by her abdominal movements into a disk, known as a basal plate. Then she crawls underneath the basal plate and continuously turns around in circles spinning the cylindrical wall. The palps are held in contact with one side of this wall while spinnerets are placed on the opposite wall. After about two hours, the cylindrical wall grows to 5 mm in height. Cocoon size is directly related to the size of the spider, but not necessarily to the number of eggs it will hold. Females wait for a few minutes and begins to lay eggs and cover them in a tight pack of silk threads. This becomes the cover plate and the spider continues to add layers of thread to it. The loop mesh ultimately wraps around the entire surface of the egg sac. Females remain close to the cocoon for the next few days in case the threads need repairing. Females die a few days after the egg sac is built. The cocoon will appear unchanged externally while the spiderlings develop for a few months. The offspring emerge in spring and release fine threads of silk from their spinnerets to be carried off by the wind to new locations. Their journey through the air is called ballooning. Wherever each spider drops from the sky will be where its new life begins. (Dewey, 1993; Foelix, 1982; Preston-Mafham and Preston-Mafham, 1996)

  • Parental Investment
  • no parental involvement
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female

Behavior

This species rebuilds its web everyday to enhance the possibility of capturing prey. The protein composition of spider silk is unusual. Amino acids with short side-chains make up 50 to 60% of the total protein. Before building a new web, a spider eats its old web, conserving silk proteins (Foelix 1982). The web of Araneus diadematus usually has 25 to 30 radial threads forming regular angles of 12 to 15 degrees. Webs of young individuals often have many more radii than those of adults. (Foelix, 1982)

Communication and Perception

Araneus diadematus individuals integrate information from the central nervous system and visual system. A spider will orient its body axis perpendicular to the path of a moving object in order to view the object with the main eyes. Input from the secondary eyes causes the spider to turn without any visual feedback. However, when a moving object is viewed only by the secondary eyes, a spider will not always turn towards it.

Food Habits

The ultimate purpose of spider webs is to capture prey and orb webs are well-suited for this. They are highly geometrical, with the hub slightly higher than the center so that the spider may run down the web quickly. The area nearer the hub is coated more densely with sticky globules. Araneus diadematus individuals spend most of their time on the web's hub monitoring vibrations in the silk with their sensitive legs. Females rest on one side of the web and monitors by holding onto a signal thread. When catching prey, Araneus diadematus individuals wrap prey in silk thread before consuming it. After killing and wrapping their prey, these spiders may not immediately consume the prey. The number of prey attacked and killed may decrease as the number of prey increases and the spiders become satiated. Spiders eat primarily arthropod prey. (Foelix, 1982; Preston-Mafham and Preston-Mafham, 1996; Wise, 1993)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods

Economic Importance for Humans: Positive

Araneus diadematus individuals feed on insects, helping to reduce the population of insect pests. People can use clean spider's web on a cut or wound to stop bleeding. (Foelix, 1982; Parsons, 1990)

  • Positive Impacts
  • controls pest population

Conservation Status

There is no special conservation status for this species.

Other Comments

Araneus diadematus is a large species and the best known of all orb weavers. (Comstock, 1980)

Contributors

Veronica Godines (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

Comstock, J. 1980. The Spider Book. United Kingdom: Cornell University Press Ltd.

Dewey, J. 1993. Spiders Near and Far. New York: Dutton Children's Books.

Foelix, R. 1982. Biology of Spiders. Cambridge, Massachusetts: Harvard University Press.

Kaston, B. 1972. How To Know the Spiders. Dubuque, Iowa: Wm. C. Brown Company Publishers.

Parsons, A. 1990. Amazing Spiders. New York: Alfred A. Knopf, Inc..

Preston-Mafham, K., R. Preston-Mafham. 1996. The Natural History of Spiders. Ramsbury, Malborough: The Crowood Press Ltd.

Wise, D. 1993. Spiders in Ecological Webs. New York: Cambridge University Press.

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