Yellow garden spider

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iYellow garden spider
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Arachnida Order: Araneae Family: Araneidae Genus: Argiope Species: A. aurantia
Binomial name
Argiope aurantia Lucas, 1833

The Black and Yellow Garden Spider (Argiope aurantia syn. Miranda aurantia, Epeira riparia), also known as the American Garden Spider or Writer Spider is a species of spider common to the lower 48 of the United States, southern Canada, Mexico, and Central America. They have distinctive yellow and black markings on their abdomens and a mostly white cephalothorax. Males range from 5 to 9 mm; females from 19 to 28 mm. They are one of many species of Orb-web spider. Orb-web spiders build circular webs which serve a dual purpose as full-time residence and place of business.

Contents 1 Description 2 Habitat 3 Webs 4 Reproduction 5 Adolescence 6 External links

[edit] Description

The female of the species grows much larger than the male. Females can reach 40 mm (one and a half inches) (excluding legs) and have large rounded bodies, while males are skinny-bodied and only 20 mm (¾") long. Their legs are vivid black and can have banding in various colors. Adding legs, the female can be an impressive 75 mm (3") in diameter.

The spider is striking in appearance with distinct yellow and black markings that make identification easy. Despite the bright yellow color and banding, the garden spider is not easy to spot while walking past and blends perfectly into partially sunlit areas. At first introductions they look menacing, but are harmless to humans. The spider is interesting and easy to observe through the summer because it takes up permanent residence in one location the entire season. Generally if you find one spider, others will be in the vicinity.

[edit] Habitat

The circular or orb part of the female web can be two feet in diameter and webs are built at elevations from two to eight feet off the ground but not high in trees.

Garden Spiders build webs in areas adjacent to open sunny fields where they stay concealed and protected from the wind. The spider can also be found along the eves of houses and outbuildings or in any tall vegetation where they can securely stretch a web. Information signs in parks are good places to find these spiders if the sign is tucked half-hidden in brush that adjoins an open field or marsh.

The Garden Spider has a niche that places them on the edge of open spaces where a rich variety of flying insects naturally congregate. This includes the edges of yards and gardens, and is probably the source for their name.

A hiker rummaging through brush on the edge of a field or a child retrieving a ball from behind bushes can sometimes enjoy an exciting face-to-face encounter. The spider doesn't attack and if one walks through a web, the spider will briskly exit down the arm while the person flails around screaming. The spider is quite fragile and easily killed by the slightest blow. If you find yourself immersed in one of these webs, the best course is merely back away. The web will stay partially intact and the spider will rebuild the following day.

[edit] Webs

The web consists of several radial lines stretched among four or five anchor points that can be three or more feet apart. The web lines are attached to firm stationary objects, for example the side of a building, pole, tree or bush. The radial lines meet at a central point. The spider makes a frame with several more radial lines and then fills the center with concentric circles of silk leaving a 5/16" to 3/8" gap between successive rings. The female's web is substantially larger than the male who builds a small zig-zag web nearby.

The male does not occupy the female's web, and when he finally enters the web to mate, he remains for a few days but stays well back from the big female. He appears to be waiting for the opportune moment or invitation. The female will eat the male and anything else that wanders into the web.

When disturbed, the spider oscillates her web vigorously back and forth while she remains firmly attached in the center. This action might prevent predators like wasps and birds from drawing a good bead. Likely this method is used to catch insects that flutter close, and also to fully entangle an insect before it cuts itself loose. The spider is able to stop the oscillations quickly, which indicates it has a masterful grip on its environment.

Only when directly perturbed (like passing the shadow of your hand over its web or poking the spider with a pencil) does the spider abandon its center position and run to the edge of the web, otherwise the spider remains inverted in the web, with head facing downward, for its entire one-summer lifespan. The spider stays with the web continually except when it leaves one night in late summer to lay eggs.

As a footnote, the spider becomes accustomed to passing shadows caused by your hand once the stimulus is repeated several days in a row. Progressively the spider responds less and less until it barely reacts after about four days. However if you stop giving the stimulus for a length of time, and then do it again later, the spider will again respond, but it won't run as far, and stops responding more quickly than the first time the sequence was performed.

The observations show that Garden Spiders can differentiate threats and decide which to ignore. It also shows they are not genetic automatons and can learn from experience. The reaction to shadows is most likely a defensive strategy against incoming birds and animals.

Because the spider also responds to shadows at nighttime, it probably means bats or other night hunters, perhaps snakes, will target the spider. Evidence of nocturnal predation is bolstered since some mornings a web can be observed torn apart in the middle and the spider is missing. Obviously whatever took the spider struck quickly and was aiming for the center of the web. Furthermore, the rest of the web wasn’t disturbed as would be expected if a raccoon invaded. Most spiders however make it through the full season.

In a daily ritual, the spider consumes the circular interior part of the web and then rebuilds it each morning with fresh new silk. The spider may be recycling the chemicals used in web building. Additionally, the fine threads that she consumes appear to have tiny particles of what may be miniscule insects and organic matter that may contain nutrition.

The full radial framework and anchoring lines are not replaced daily. The spider uses all eight legs in the rebuilding process and bends the radial lines slightly together while applying silk so the new web is stretched taut. The spider starts with the innermost ring and moves successively outward in a clockwise motion. Watching the spider rebuild her web is like watching a geometric ballet, but you have to get up at first sun to see it, and by then she's already at work.

After rebuilding the web, the spider makes a dense zig-zag pattern of silk in the center to conceal her presence. The spider remains motionless throughout the heat or rain until a hapless morsel is snared. The spider cocoons the catch and later removes it to the center of the web to be consumed like a malted milk. Afterwards the cocoon is dropped to the ground where ants have been seen carting off the leftovers. Normally the spider stays on the same side of the web throughout the season, however if aggravated enough by the observer they will reverse sides.

The web normally remains in one location for the entire summer, but spiders can change locations usually early in the season, perhaps to find better protection or better hunting. Interestingly, when they relocate, they don't go far but they remove the entire web from its previous location. Perhaps removal of the web is to conceal whereabouts from prey and active predators. The web may also contain vital ingredients needed for the next web.

Female webs can exist as close as ten feet from each other, but there is usually considerable distance between webs. The Garden Spider doesn't live in dense clusters like other similar-in-appearance orb spiders such as the Golden Orb Web Spider. And the Garden Spider keeps a clean orderly web in comparison to the cluttered series of webs built and abandoned by groups of Golden Orb Spiders. Both species of spider are similar in many characteristics, although the Garden Spider is generally larger and has a larger web. In both species the female remains inverted in the center of the web; however Golden Orb males occupy the female web continually, whereas Garden males only enter at mating time.

Near the end of the season, usually in September, the female Garden Spider begins to neglect the web. The web is not as big or as completely rebuilt as observed earlier in the summer. At the same time the spider's abdomen grows large and round. This signals the beginning of egg-laying which takes place in less than a week.

[edit] Reproduction

The female spider lays eggs at nighttime near the web, and covers the eggs with a beige-colored sac suspended away from the surface using a thick mesh of silk. The thick silk barrier protects the eggs from insects, and also makes the sac very difficult to sweep away. Egg sacs range from 5/8" to 1" in diameter and look like miniature hot-air balloons with a gathered opening at the top. Each spider produces from one to as many as four sacs with perhaps over a thousand eggs inside each.

In the days following egg-laying, the female is thinner and begins to moves sluggishly. She also begins to lose her bright yellow color. The web falls into further neglect, and as the evenings become cooler, the female disappears from the web overnight and dies. The baby spiders hatch in the fall, but remain inside the sac until the following spring.

In the spring, the young spiders exit the sac and are so tiny that their collection of bodies look like dust gathered inside the silk mesh. You have to look very close to see that these little specs of brown dust are actually tiny moving spiders. The new generation of spiders usually rebuilds webs close to where the eggs were laid, but never exactly where a web was the year before. The same locale usually has a returning population of Garden Spiders that makes them easy to observe from year to year.

[edit] Adolescence

Out of the many egg sacs and thousands of eggs laid, only two to four adult female spiders will reappear and make webs. This leads to speculation that most young spiders don't survive or become large enough to make webs.

The transition from egg sac to full-sized spider is a mystery. Full-sized spiders seem to appear overnight, complete with a full-sized web when they weren't there the day before. So where did they go after leaving the egg sac and how did they change into large colorful adults?

Growing adolescent spiders with small webs are not observed. Or if these spiders do build webs as adolescents, those webs are not located exactly where the final adult spider emerges. This may indicate that the spiders live their adolescence as neutral-colored ambush predators, or perhaps they have very small webs concealed in crevices. In any case, the Garden Spider seems to have a growth process that leads to sudden enlargement and color-change as they emerge into adulthood.

This developmental period might seem dull compared to watching full-grown spiders; however the six-week+ adolescent stage represents a large percentage of lifetime for an organism whose entire life-cycle encompasses less than a year.

Since most of the spider's life is spent as a dust-sized speck closely packed together with others of it kind, it would be fascinating to understand their social structure. It's doubtful they are reading books during the winter-stay in the protective sac, but they must be doing something that affects which spiders reach maturity.

Because so few spiders survive to become adults, yet the returning number of adults remains virtually the same each year, it raises speculation whether the tiny newborns leave the egg-sac and make a dash for survival like Ridley sea turtle, or if the species utilizes a cooperative strategy for survival.

The mystery is illuminated slightly because 'half-sized' or 'near successful' adults are never observed building webs or occupying crevices near the egg sac. Neither do there seem to be summers with an overpopulation of the species. These two observations suggest a cannibalistic strategy where the nutrients harvested by the colony of growing spiders end up feeding two or three strong females that make it to adulthood. The question could be answered by tediously tracking the near-invisible babies or by carefully observing areas where adult spiders are likely to emerge and build webs.

Another interesting, yet entirely speculative possibility is that the spider has a dual track for propagating their kind where some members of the species are able to reproduce despite not reaching full-colored, mature status. This would explain why some years there seems to be an absence of the colorful species in areas they occupied previously.

It's also a mystery how such tiny creatures can travel hundreds of yards from where eggs sacs were seen, or how they get to areas they were not observed in before. In a natural irony, do they hitch rides on the legs of flying insects that they later eat?

Many mysteries remain since much of the spider's activity seems to take place at night and they remain well-hidden as adolescents. Evidence for night-activity comes from observations that they lay eggs at night and also change locations at night. Additionally, when they finally emerge as full-grown adults, they magically appear overnight, complete with a full-sized web, ready to do business that morning.

[edit] External links

• Pictures of the yellow garden spider
• Pictures of A. aurantia (free for noncommercial use)
• Argiope Aurantia