By Annie Peters
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. ()
Biogeographic Regions:
nearctic 
(native ); neotropical (native ).
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. ()
These animals are found in the following types of habitat:
temperate ; tropical ; terrestrial .
Terrestrial Biomes:
forest ; rainforest ; scrub forest .
Other:
suburban ; agricultural .
Physical Description
(0.08 to 0.35 in)
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. ()
Some key physical features:
ectothermic ; bilateral symmetry ; polymorphic .
Sexual dimorphism: female larger.
Reproduction
Breeding occurs during winter.
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. ()
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. ()
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. ()
Key reproductive features:
semelparous ; seasonal breeding ; sexual ; fertilization (external ).
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. ()
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. ()
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. ()
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. ()
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. ()
Other communication keywords:
vibrations .
Perception channels:
visual ; tactile ; vibrations .
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). ()
Primary Diet:
carnivore (insectivore ).
Animal Foods:
body fluids; insects; terrestrial non-insect arthropods.
Predation
- Phalacrotophora epirae
- Tetrastochus n. (eulophid wasp)- hyperparasite of G. cancriformis
- Arachnophago ferruginea
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. ()
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. ()
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. ()
Ways that these animals might be a problem for humans:
injures humans (bites or stings).
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. ()
Ways that people benefit from these animals:
research and education; controls pest population.
Conservation Status
IUCN Red List: [link]:
Not Evaluated.
US Migratory Bird Act: [link]:
No special status.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
This species is plentiful throughout the western hemisphere.
Contributors
Nancy Shefferly (editor), Animal Diversity Web Staff.
Annie Peters (author), Southwestern University.
Stephanie Fabritius (editor), Southwestern University.
