Argiope aurantia

Argiope aurantia, a photo by kevin33040 on Flickr.

Via Flickr:
"Geographic Range
These spiders are found from occur from southern Canada south through the lower 48 United States, Mexico, and Central America as far south as Costa Rica. (Milne and Milne, 1980; Platnick, 2004)


Biogeographic Regions nearctic native
Habitat
This species prefers sunny areas among flowers, shrubs, and tall plants. It can be found in many types of habitats, though is not common in the Rocky Mountains or the Canadian Great Basin. (Milne and Milne, 1980)


Habitat Regions temperate tropical terrestrial
Terrestrial Biomes savanna or grassland chaparral forest scrub forest
Wetlands marsh swamp
Other Habitat Features suburban agricultural
Physical Description
As is true in many spider species, females of this species grow to much larger size than males. Adult female body length ranges from 19 to 28 mm (3/4 to 1 1/8 in.), while males reach only 5 to 9 mm (1/4 - 3/8 in.). In both sexes, the shiny, egg-shaped abdomen has striking yellow or orange markings on a black background. The forward part of the body, the cephalothorax, is covered with short, silvery hairs. Legs are mostly black, with red or yellow portions near the body. (Dewey, 1993; Milne and Milne, 1980)


Like other orb-weavers (family Araneidae), this species has three claws per foot, one more than most spiders. Orb-weavers use this third claw to help handle the threads while spinning. Also in common with other orb-weaving spiders (and most, but not all spiders generally), A. aurantia has a venomous bite that immobilizes prey that is caught in its web. (Dewey, 1993; Milne and Milne, 1980)


Other Physical Features ectothermic heterothermic bilateral symmetry venomous
Sexual Dimorphism female larger
Development
In areas with a cold winter, the eggs of this species hatch in the late summer or autumn, but the hatchling spiders become dormant and do not leave the egg sack until the following spring. Hatchlings generally resemble small adults, there are no major changes in anatomy or structure as they grow (except the development of reproductive organs). (Dewey, 1993)


Development - Life Cycle diapause
Reproduction
Once they mature, males of this species leave their webs and wander in search of females. When they find them, they wait around the edge of her web, sometimes building small webs of their own. We don't have any information on whether males or females mate more than once, or with more than one partner. Probably each female mates with one or more males. (Faulkner, 1999; Heiber, 1992; Hieber, 1992; Milne and Milne, 1980)


Mating System polygynandrous (promiscuous)
After mating, each female produces one or more (rarely 4, usually less) brown, papery egg sacs. They are roughly round in shape and up to 25 mm in diameter; each contains 300 to 1400 eggs. She attaches her egg sacs to one side of her web, close to her resting position at the center. (Faulkner, 1999; Heiber, 1992; Hieber, 1992; Milne and Milne, 1980)


Key Reproductive Features seasonal breeding gonochoric/gonochoristic/dioecious (sexes separate) sexual fertilization internal oviparous
Breeding interval
Once per year
Range number of offspring
300 to 1400
Each female watches over her eggs as long as she can, but she will die in the first hard frost, if not before. (Faulkner, 1999; Hieber, 1992)


Parental Investment no parental involvement pre-fertilization protecting female pre-hatching/birth provisioning female protecting female
Lifespan / Longevity
In temperate climates, the great majority of individuals live a little over a year: from their hatching in the fall until the first hard frost in the following year. However, in warmer climates and in captivity females of this species may live for several years. Males probably die after mating in their first year.


Behavior
If the climate is suitable, Argiope spiders may be active both day and night, attacking insects that are trapped in its web. They often construct and repair their webs after dark, but may do this in day time too. Once they find suitable sites for their webs, they will tend to stay there unless the web is frequently disturbed, or they can't catch enough food there. As noted earlier, adult males roam in search of potential mates, but once they find a female they build small webs nearby and court her. (Dewey, 1993; Dewey, 1993; Faulkner, 1999; Milius, 2000)


Key Behaviors diurnal nocturnal crepuscular motile sedentary hibernation solitary
Communication and Perception
These spiders have relatively poor vision, but are quite sensitive to vibration and air currents. Males communicate with potential mates by plucking and vibrating the females' webs. (Dewey, 1993)


Communication Channels visual tactile chemical
Other Communication Modes vibrations
Perception Channels visual tactile vibrations chemical
Food Habits
Like all spiders, black-and-yellow argiopes are carnivorous. They spin an orb web to capture small flying insects such as aphids, flies, grasshoppers, and Hymenoptera (wasps and bees). A female can take prey up to 47mm in diameter, up to 200% of her own size (Nyffeler et al. 1987)


The web can be up to two feet across. The spider hangs, head down, in the center of their web while waiting for prey. Often, she holds her legs together in pairs so that it looks as if there are only four of them. Sometimes the spider may hide in a nearby leaf or grass stem, connected to the center of the web by a nonsticky thread which quivers when prey lands in the web.


Web construction is complicated. To start the web, Argiope firmly grasps a substrate like a grass stem or window frame. She lifts her abdomen and emits several strands of silk from her spinnerets that merge into one thread. The free end of the thread drifts until it touches something far away, like a stem or a flower stalk. She then creates bridge lines, and other scaffolding to help her build the framework of the web. She builds a hub with threads radiating from it like a spokes of a wheel. She switches to sticky silk for the threads spiraling around this hub that will actually catch her prey. It may take a few hours to complete the web, then she eats the temporary scaffolding and the center hub. Argiope spiders often add stabilimenta, or heavy zig-zagging portions, in their webs. A stabilimentum may or may not aid prey capture (see below). The entire web is usually eaten and then rebuilt each night, often in the same place. (Dewey, 1993; Faulkner, 1999; Lyon, 1995; Milne and Milne, 1980; Nyffeler, et al., 1987; Zschokke, 2006)


Primary Diet carnivore insectivore
Animal Foods insects terrestrial non-insect arthropods
Predation
When disturbed, the spider might first vibrate the web to try to make its body look bigger, but if that fails to deter a predator she will drop to the ground and hide (Faulkner 1999). Adults may be captured by wasps such as the Blue Mud Dauber, Chalybion californicum (Landes et al. 1987). They are also eaten by birds, lizards, and shrews.


Overwintering egg cases protect spiderlings from predation. Suspending the cocoon from the web is particularly effective against ant predation. The vast majority, however, are eventually damaged by birds. Cocoons wall layers provide barriers against burrowing larvae of insect predators and ovipositors of parasitic insects, but ichneumonid wasps such as Tromatopia rufopectus and chloropid flies such as Pseudogaurax signatus lay their eggs in Argiope aurantia egg cases. In fact, one study found that in addition to A. aurantia, nineteen species of insects and eleven species of spiders emerged from A. aurantia egg cases. (Hieber 1993, Lockley and Young 1993). (Faulkner, 1999; Hieber, 1992; Landes, et al., 1987; Lockley and Young, 1993)


Anti-predator Adaptations aposematic
Economic Importance for Humans
Economic Importance for Humans: Positive
Researchers study the biochemistry of web production and venom action of this spider. Results from these studies may aid the fields of materials science and neurophysiology.


Argiope species are important predators of grasshoppers in rangeland ecosystems.


Conservation Status
These common and widespread spiders have no special conservation status.


IUCN Red List [Link]
Not Evaluated
US Federal List
No special status
CITES
No special status
State of Michigan List
No special status
Other Comments
Although people are concerned about being bitten by these large spiders, they are not considered dangerous. They may bite when harassed, but apparently the venom does not cause problems for humans. (Lyon 1995)


The function of web stabilimenta is controversial. At least 78 species of spiders add these structures to their webs, originally named "stabilimenta" because they were thought to provide structural stability. One study of Argiope spiders supports the idea that these bright white structures attract flying insects (Tso 1998). Contrary to this "prey attraction hypothesis," hungry spiders build fewer or smaller stabilimenta, and webs with stabilimenta capture fewer prey (Blackledge 1998, Blackledge and Wenzel 1999). A competing hypothesis is that the highly visible threads prevent birds from flying through and destroying the webs. Spiders of another species, Octonoba sybotides, vary their stabilimenta in order to control thread tension. Different tensions allow a spider to detect prey of different sizes. However, this mechanical hypothesis doesn't explain why only diurnal spiders use stabilimenta. (Milius 2000). (Blackledge and Wenzel, 1999; Blackledge, 1998; Lyon, 1995; Milius, 2000; Tso, 1998)"

Taken as it appeared from animaldiversity.ummz.umich.edu/accounts/Argiope_aurantia/ on September 11, 2013.