Gasteracantha cancriformis

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Geographic Range

Gasteracantha cancriformis is found in many parts of the world. It is found across the southern part of the United States from California to Florida, as well as in Central America, Jamaica, and Cuba. (Levi, 1978)

Habitat

Spiny crablike orb weavers, G. cancriformis, live in woodland edges and shrubby gardens. Many of the studies on this spider have taken place in citrus groves in Florida. They frequently live in trees or around trees in shrubs. (Levi, 1978; Muma and Stone, 1971; Muma, 1971)

Physical Description

Gasteracantha cancriformis showed marked sexual dimorphism in size. Females are 5 to 9 mm in length and 10 to 13 mm in width. Males are 2 to 3 mm long and a small amount shorter in width. Six abdominal spines are present in all morphs, but color and shape show geographic variation. Most individuals have white spots on the underside of the abdomen, but the color of the back and spines may be red, orange or yellow. Also, a small number of spiders have colored legs. (Levi, 1978; Muma, 1971)

  • Sexual Dimorphism
  • female larger
  • Range length
    2 to 9 mm
    0.08 to 0.35 in

Reproduction

The only known observations of mating behavior occured in a laboratory environment where there was only one female and one male to work with. It is assumed that the mating system in nature is similar to, if not the same as, that observed in the laboratory environment. However, scientists are not sure whether these animals are monogamous or polygamous. (Muma, 1971)

Laboratory studies of mating behavior show that males visit female webs, and use a 4-tap rhythmical-pattern drumming on the silk of the web. After several cautious approaches, males approach females, become strapped down with silk from the female, and copulate. Mating may take 35 minutes or more. After mating, the male remains on the female's web. Mating may occur repeatedly. (Muma, 1971)

While facing down near the center of her web, the female produces an egg sac with 100 to 260 eggs. She deposits the sac on the underside of leaves near the nest, then dies. The eggs must hatch and survive without parental care over the winter, then spiderlings disperse in the spring when they are able to spin webs and produce eggs (females) or fertilize eggs (males) on their own. Both males and females reach maturity within 2 to 5 weeks of age. (Milne and Milne, 1980)

  • Breeding season
    Breeding occurs during winter.
  • Range number of offspring
    100 to 260
  • Range age at sexual or reproductive maturity (female)
    2 to 5 weeks
  • Range age at sexual or reproductive maturity (male)
    2 to 5 weeks

All parental care in crablike orb weavers occurs before the young hatch. After the female lays an egg mass, she dies. The eggs are left to hatch and the spiderlings to disperse. In order to protect and feed the young in their egg and larval stages, the female constructs an egg case. In nature, the case is constructed on the bottom and sometimes the top of the leaves on trees where the web is located, but not on limbs or trunks of trees. The case is constructed first from an ovate egg sheet made of loosely woven fine threads which are firmly attached to the lower leaf surface with strong attachment disks. The eggs are distributed upward on the platform in a long, ovate mass. The female covers the egg mass with a loose, spongy, tangled mass of yellow and white threads, fastened with the same type of disks used before. Another covering is made when the female moves along the mass, loosely covering it with several dozen coarse, rigid, dark green threads. These threads form a distinct longitudinal line on the case. The final cover is a net-like canopy, spun over the mass and attached to a leaf. Hatched spiderlings take a few days to learn how to move correctly, and under undisturbed, natural conditions do not disperse from the case for 2 to 5 weeks. (Muma, 1971)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

This species of spider does not live very long. In fact, the lifespan only lasts until reproduction, which usually takes place the spring following the winter when they hatched. Females die after producing an egg mass, and males die six days after a complete cycle of sperm induction to the female. (Levi, 1978; Milne and Milne, 1980; Muma, 1971)

  • Typical lifespan
    Status: wild
    1 (high) years

Behavior

Development of spiny orb weavers takes place late in the year, and a new web is constructed each night to make sure that the structure is secure. Webs are constructed mostly by adult females because male species typically hang from a single thread close by the nest of a female. The web hangs at a slight to distinct angle from perpendicular, where the female rests near the bottom, facing down, awaiting her prey.

The web itself is constructed of a basic foundation which consists of a single vertical strand. The foundation is connected with a second primary line or by a primary radius. In both situations, the structure is pulled together into an angle that causes three convergent primary radii. Sometimes, more than three primary radii are constructed. After making this basic framework, the spider begins to construct a strong exterior radius, then continues to spin secondary non-viscid radii which are attached to the partly spiraled, random lined, central disk. The difference between foundation silk and tufted silk is visibly distinct. (Milne and Milne, 1980; Muma and Stone, 1971; Muma, 1971)

Females live solitarily on individual webs. Up to three males may dangle on silk threads nearby. Females can be found at any time of the year, but mostly from October to January. Males can be found during October and November. The webs can be found 1 to 6 meters above ground. Activity is diurnal, so these spiders are easily collected for studies. (Levi, 1978; Muma, 1971)

Communication and Perception

Visual communication is used during courtship. Upon contact with each other, the spiders vibrate the web. Males use a rhythmic pattern when vibrating the web during courtship. These spiders also move up and down their silk lines to show a reaction to other creatures. It is likely that there are patterns for this also. (Muma, 1971)

Food Habits

Females build webs that they use to capture prey. A female sits facing down in her web, awaiting her prey on the central disk. When a small insect flies into the web, she moves toward it, then snaps the radii on either side of the insect. In order to secure the prey, the spider snaps more of the web around the area, then rushes toward the prey in order to determine its exact location and bite it before carrying it back to the central disk where she feeds.

To carry a prey item back to the central disk, the female either climbs back up the web with her food, or swings down a drag line then climbs up to her resting area. If the prey is smaller than the spider, she will just paralyze it, carry it to her spot, and eat it without wrapping it up. If the prey item is larger than the spider, it requires wrapping before being carried to the central disk.

Sometimes several prey insects become caught in the web at the same time, so that the spider must find and paralyze them all. If it is not necessary to carry them away to eat them, the spider may just feed on them where they are, then come back to them as she pleases.

Gasteracanta cancriformis feeds upon the liquified insides of her prey. Deliquified carcasses are discarded from the web and are easily recognized in their mummified state.

Foods eaten: drosophilids, whiteflies, beetles, moths, other small fly species (none appear to have been rejected). (Muma, 1971)

  • Animal Foods
  • body fluids
  • insects
  • terrestrial non-insect arthropods

Predation

Crablike spiny orb weavers probably received this common name because of the spines on their backs. These spines may have an anti-predator function. These spiders are also very small, making it hard for a predator to see them and attack them. The spider eggs are often attacked by parasitoid wasps and flies. (Levi, 1978; Muma and Stone, 1971)

  • Known Predators
    • Phalacrotophora epirae
    • Tetrastochus n. (eulophid wasp)- hyperparasite of G. cancriformis
    • Arachnophago ferruginea

Ecosystem Roles

In nature, this species preys upon many small insect pests that are present in crops and suburban areas. It helps to control overpopulation of such insects. (Muma and Stone, 1971)

Economic Importance for Humans: Positive

This tiny spider is an interesting species for study and research. Additionally, the fact that G. cancriformis preys on small insects in citrus groves helps farmers to control pests. Since there is clinal variation in these animals in the different areas where they are found, researchers are able to study genetic variation, clines, and adaptations to a specific environments. (Muma, 1971)

  • Positive Impacts
  • research and education
  • controls pest population

Economic Importance for Humans: Negative

These spiders can bite, but they are not of much harm to humans. Humans can be bothered by the species' spines, which may cause a puncture in skin if touched in the wrong place. So, although they eat insects in orchards, which is beneficial, they become a pest during harvest time. (Muma and Stone, 1971)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

This species is plentiful throughout the western hemisphere.

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Annie Peters (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

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

agricultural

living in landscapes dominated by human agriculture.

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

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

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

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

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.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

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

suburban

living in residential areas on the outskirts of large cities or towns.

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

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Levi, H. 1978. The American orb-weaver genera Colphepeira, Microtheno, and Gasteracantha North of Mexico. Bull.Mus.Comp.Zool., 148: 417-442.

Milne, L., M. Milne. 1980. The Audubon Society Field Guide Series. New York: Alfred A. Knopf Inc..

Muma, M. 1971. Biological and Behavioral notes on *Gasteracantha cancriformis* (Arachnida: Araneidae). Florida Entemol., 54: 345-351.

Muma, M., K. Stone. 1971. Predation of *Gasteracantha cancriformis* (Arachnida: Araneidae) eggs in Florida citrus groves by *Phalacrotophora epeirae* (Insecta: Phoridae) and *Arachnophaga ferruginea* (Insecta: Eupelmidae). Florida Entemol., 54: 305-310.