Pisaurina mira

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Geographic Range

Nursery web spiders, Pisaurina mira, are found in Western and Southern Europe, including the British Isles. Nursery web spiders are also found in Ontario, Quebec, and Nova Scotia. In addition, this species is found in the United States, ranging from Florida, west to Texas and north to Kansas and Minnesota. (Milne and Milne, 1980; Pfeffer, 1989)

Habitat

Nursery web spiders inhabit fields, meadows, and woods. Pisaurina mira also likes to live in tall grass, shrubs, and bushes. Some are even found in houses. Nursery web spiders like tropical areas. (Milne and Milne, 1980; Pfeffer, 1989)

Physical Description

Nursery web spiders have bodies similar to those of other spiders. They have a combined head and thorax region called the cephalothorax, and an unsegmented abdomen region. The cephalothorax and the abdomen are joined by the pedicel, which is narrow and allows for flexibility. The cephalothorax has a hard covering called the carapace for protection. The abdomen is usually sac-like and contains the heart, midgut, silk glands, respiratory and reproductive systems. Spiders also have six pairs of appendages: eight legs, two palps (the male's palps bearing a copulatory organ) and a pair of jaws (chelicerae).

Male nursery web spiders are 9 to 15 mm long and the females are usually 12 to 15 mm long. Both males and females are yellowish-brown in color and sometimes have a light to dark brown band down the middle of the back. A narrow white border is present around the abdomen. These large spiders greatly resemble wolf spiders and are usually mistaken for them.

Nursery web spiders have eight eyes which are arranged in two rows. The front row has a straight line of four eyes, and the back row has the remaining four eyes in a U shape. There are three claws on each tarsus (part of an arthropod leg immediately distal to the tibia, usually divided into a number of segments or tarsomeres). (Leftwitch, 1976; Milne and Milne, 1980; O'Toole, 1986)

  • Sexual Dimorphism
  • female larger
  • Range length
    9 to 15 mm
    0.35 to 0.59 in

Reproduction

The first step in the reproduction of nursery web spiders is courtship. Male spiders usually court a female by offering her a "nuptial gift." The male captures a fly or some other insect and spins a cocoon around it, then offers it to the female. This offering can last for quite some time and is often repeated. Some females, however, are not ready to mate and threaten their suitors. Females unwilling to mate chase their suitors away. When a nuptual gift is accepted, the male completes copulation. He often takes the nuptial gift back from the female.

Mating occurs in mid-June to mid-July. When a female is ready to lay her eggs, she uses her cheliceres and maxillipeds (grasping mouthparts) to transfer eggs into a cocoon under her abdomen. She carries this sac underneath her body with her fangs (cheliceres) until hatching time approaches. The female then builds another cocoon where she feels it will be safe for the spiderlings. She lashes surrounding leaves together forming a kind of "nursery web" for which the species is named. The female stays there, watching over her brood of pulli (first stage larvae), until they have completed their first larval molt.

Spiderlings molt several times. When a spider molts, a new larger skin replaces the skin that has grown too tight. The spiderlings are ready to leave the nursury after the first molt and the female is free to go. (Grzimek, 1972; Milne and Milne, 1980; Pfeffer, 1989)

  • Breeding season
    Breeding occurs in mid-June through mid-July.

Female nursery web spiders provide a great deal of parental care to their offspring. They first spin a cocoon for the eggs, and carry that sac safely under their abdomens until it is time for the young to hatch. Then, females construct their nursery web in which the young spiderlings live. Until the time of the first molt, the young are protected by the mother. Males are not known to share a role in parental care in this species. (Grzimek, 1972; Milne and Milne, 1980; Pfeffer, 1989)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • protecting
      • female
  • pre-independence
    • protecting
      • female

Behavior

Nursery web spider females do not usually kill or eat their male suitors, but males don't take a chance on it. Some have been known to spin a web around the females like a rope in order to keep a safe distance. However, a female can break the silk quite easily when mating is done.

When P. mira is being chased by a predator, it will run away. The escape can be spectacular if the spider happens to run straight for a pond or lake. Nursery web speiders have been known to run over the water if pursued, and will sometimes even dive underwater to escape. (Milne and Milne, 1980)

Home Range

Home range size for this species has not been reported.

Communication and Perception

Communication in this species has not been well-studied. During mating, the offering of a nuptual gift implies some visual communication, although some tactile information may be used in assessing a nuptual gift also.

Food Habits

Pisaurina mira is not the type of spider that builds a web and waits for insects to land and get tangled in it. It is an active hunter which wanders over vegetation looking for small insects to catch. Nursery web spiders have been known to occasionally capture larger insects and tadpoles.

While hunting, nursery web spiders slowly makes their way among the grassy stalks and leaves, where they wait for insects like gnats and mosquitoes to come within reach of their cheliceres (clawlike pincers). The venom of nursery web spiders is not very strong, and it could not kill something bigger than a fish, but a single bite is usually enough to pierce the body wall of an insect and kill it instantly. These spiders inject digestive juices into their prey, liquifying the internal organs of the prey. This then allows the spiders to ingest the resulting soup. (Milne and Milne, 1980; Pfeffer, 1989)

  • Animal Foods
  • amphibians
  • insects
  • terrestrial non-insect arthropods

Predation

Hunting wasps, including Sceleriphon and species of the Pompilidae, are probably the most frequent predators of nursery web spiders. There are other species of parasitic wasps that prey specifically on the embryos or various larval stages of P. mira. As is generally the case with spiders, cannibalism is quite prevelant too. It is likely that small mammals, birds, and amphibians could prey upon P. mira. When pursued by predators, these spiders run away. (Milne and Milne, 1980; Pfeffer, 1989)

Ecosystem Roles

It is likely that these spiders have some impact on insect populations.

Economic Importance for Humans: Positive

There is no specific economic importance for this particular species, but like all spiders they help in keeping the insect population in check.

Economic Importance for Humans: Negative

Nursery web spiders are not harmful to humans. Their bite can not kill anything bigger than a small fish. (Pfeffer, 1989)

Conservation Status

Nursery web spiders are common in many parts of their range. They are not a particular conservation concern. (Milne and Milne, 1980)

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Cristy Torres (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

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

arboreal

Referring to an animal that lives in trees; tree-climbing.

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

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

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.

seasonal breeding

breeding is confined to a particular season

sexual

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

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

Grzimek, D. 1972. Grzimek's Animal Life Encyclopedia. New York: Van Nosrand Reinhold Company.

Leftwitch, A. 1976. A Dictionary of Entomology. New York: Crane and Russak Company,Inc..

Milne, L., M. Milne. 1980. The Audubon Society Field Guide to North American Insects and Spiders. New York: Chanticleir Press.

O'Toole, C. 1986. The Encyclopedia of Insects. New York: Facts on File Inc..

Pfeffer, P. 1989. Predators and Predation. New York: Facts on File Inc..