Life cycle of a Garden Spider

The Black and Yellow Argiope or Argiope Aurantia, also known informally as the Garden Spider, is one of many species of Orb-web spider. Orb-web spiders build circular webs which serve as a full-time residence during their single-year lifespan. The spider is common to the lower 48 states, southern Canada, Mexico, and Central America.

The yellow garden spider is a species of spider common to the lower 48 states, southern Canada, Mexico, and Central America. They have distinctive yellow and black markings on their abdomens and a mostly white cephalothorax.

The female of the species grows much larger than the male. Females can reach one and a half inches (excluding legs) and have large rounded bodies, while males are slim and 3/8 to 3/4” long. Legs of both male and female are yellow and vivid black with banding in various colors. Adding legs, the female can reach an impressive 3” in diameter but not all adult females become that large and some can be rather small and difficult to locate.

The spider’s striking yellow and black markings make identification easy, but despite this coloration, the Garden Spider blends perfectly into partially sunlit areas. At first encounter they look menacing, but are harmless to humans and easy to observe because they stay in one area the entire summer. Normally if you find one spider, others will be in the vicinity nearby.

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

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 any tall vegetation where a web can be securely attached. 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 niche places them on the edge of open spaces where a rich variety of flying insects congregate. This includes the edges of yards and gardens, and is probably the original source for their name.

A hiker rummaging through the 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 exit down the arm while the person flails around screaming. The spider is quite fragile and easily killed by the slightest blow. Once 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.

The web consists of several radial lines stretched among 4 or 5 anchor points that can reach six or more feet apart. The web lines are attached to firm stationary objects like a building, pole, tree or bush. The radial lines meet at a central point, and to this basic struucture the spider adds a framework with more radial lines. The web is finished with circles of silk spaced 3/16" to 3/8" between successive rings depending on the size of the spider. Webs contain innumerable irregularities with various degrees of pitch and no two are exactly alike. However most Garden Spiders seem to angle their web at 75°-80° and will stay on the most inverted side. The female's web is substantially larger than the male who builds a smaller zig-zag web nearby.
 
The male does not occupy the female's web, and when he finally enters the web to mate in late July or early August, he remains for a few days but stays well back from the big female. He appears to wait on the edge for an opportune moment or invitation. The female will eat the male and anything else that enters 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 on their prey. This action is also used to catch insects that flutter too near the web, and also to fully entangle an insect before it can cut 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 waits inverted in the web, with head facing downward for its entire one-summer lifespan. The spider does leave its web when it changes locations at night and also 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 four consecutive days. However if the stimulus is stopped for a length of time, and then repeated later, the spider will again respond, but won’t run as far, and stops responding more quickly than the first time the sequence was performed. Not every spider responds to this stimulus either.

These observations indicate that Garden Spiders can differentiate threats and decide which to ignore. It also shows they are quite aware of their surroundings and can learn from experience. The reaction to shadows is most likely a defensive strategy against incoming birds and animals.

Some spiders also responds to shadows at nighttime, which 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. It appears whatever took the spider struck quickly and was aiming for the center of the web. Most adult 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 being consumed appear to have particles of what may be miniscule insects and organic matter stuck to the web that could contain nutrition.
 
The full radial framework and anchoring lines are not replaced daily unless the spider changes location. The spider uses its legs in the rebuilding process and bends the radial lines slightly together while applying silk so the new web is stretched taut. Even a spider missing three legs on one side of its body can rebuild a web. The spider starts with the innermost ring and moves successively outward in a clockwise motion, but every spider is different. Watching the spider rebuild is like watching a geometric ballet, but you have to get up at first sun to see the entire process. 

After rebuilding the web, the spider makes a dense zig-zag pattern in the center to conceal her presence, and then remains motionless throughout the heat or rain until a moth, wasp, dragonfly or other insect is snared. The spider prepares the catch and later removes it to the center of the web to be consumed with a soda-straw appendage in the spider’s mouth. After depleting the nutrients, the carcass is dropped to the ground where it successively feeds smaller forms of life.

Normally the spider stays on the same side of the web throughout the season, however if aggravated enough by the observer it will reverse sides. Minor aggravation doesn’t seem to cause location change, but if the web is repeatedly knocked down, the spider will move, although usually not very far away. Spiders learn quickly not to rebuild where passing people dislodge their anchor lines.

Once a spider has found a location that it likes, it will rebuild its web over and over in that spot for the rest of the summer. Some spiders continually change locations throughout the season, perhaps looking for 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, but they leave a line of silk that indicates the direction they’ve gone. Since they intentionally remove all the radial lines of the web before changing locations, it shows they understand the complicated sequence of movements needed to accomplish the work. This shows that Garden Spiders are not genetic automatons, but instead carry out very complex behaviors.

Female webs can exist close to each other, and sometimes they can be seen in pairs, but usually they stay apart from each other, and the webs are usually not connected with each other. However these spiders are extremely variable, and every summer seems to bring new surprises. The Garden Spider doesn't live in dense web clusters like other similar-in-appearance orb spiders such as the Golden Orb Web Spider, also called Banana Spiders.

There are a lot of similarities and differences in the two types of spiders. They both reach the same size and have similar webs and similar body structures although their color-markings are dissimilar. The Garden uses a white silk and the Banana uses a golden silk. The Garden Spider keeps a clean orderly web in comparison to the cluttered series of webs built and abandoned by groups of Banana Spiders. The Garden Spider makes a zig-zag pattern of silk in the center of the web to conceal its presence, while the Banana has no disguise and remains openly visible. The web differences illustrate nature’s diverse approach to the basic business of trapping insects.
 
Both species build their orb webs near open sunny areas, but the Garden Spider doesn’t build high in trees. Both species oscillate their webs to ensnare insects. Females in both species remain inverted in the center of the web; Females are larger than the males; and both species of females eat the smaller male. However Banana males occupy the female web and are always near at hand while Garden Spider males have a separate web nearby and apparently only enter the female web at mating time. Interestingly, sometimes both spider species can be seen within feet of one another.
 
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 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 late August or early September.

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, and also makes the sac very difficult to sweep away. Egg sacs can remain hanging in position for a couple years after the babies leave. The sacs slowly deteriorate perhaps from fungus or bacteria but nothing seems to get near them, implying that they have limited nutritional value or they contain the spider’s venom.

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. A spider that produces multiple sac will cluster them in a group sometimes just inches apart.

In the days following egg-laying, the female is thinner and begins to moves sluggishly. She also starts to lose her bright yellow color. The web falls into further neglect, and as the evenings cool, 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 the little specs of brown dust are actually tiny moving spiders. At this stage they seem indistinguishable from many other species of baby spider. The new generation usually rebuilds webs close to where the eggs were laid, but never exactly where a web was built the year before. The same general area usually has a returning population of Garden Spiders that makes them easy to observe from year to year.

Adolescence:

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

Large numbers of growing adolescent spiders with small webs are not observed. This may indicate that their adolescence is spent living in tiny webs that remain well hidden. In any case, the Garden Spider seems to have a growth process that leads to sudden enlargement as they emerge into adulthood and build full-sized adult webs. This might depend on the spider’s ability to catch good nourishment at just the right point in their life-cycle.

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 in the egg sac, it would be fascinating to understand their social structure. It’s unknown what they do during the winter-stay in the protective sac, but it must affect which spiders reach maturity. 

The returning number of adults remains unchanged from year to year, and this raises question whether the tiny newborns leave the egg-sac and make a dash for survival, or if the species utilizes 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.

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 the baby spiders hitch rides on the legs of flying insects that they later eat? Or do they travel by silk threads that sometimes can be seen floating across open areas.
 
Spiders are everywhere and so is the silk they use. Catching sunlight coming across a low-cut field shortly before sunset, one can see silk running from nearly every stalk of plant to the next in an endless array of pathways. Also looking at the same light coming through panes of window glass shows the entire surface is streaked with strands of silk. It appears the world is covered with web material, but how the Garden Spider travels and communicates through this maze is unknown.

Many mysteries remain since much of the Garden Spider’s activity seems to take place at night, plus 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 appear overnight, complete with a full-sized web, ready for business that morning.

The Garden Spider’s life-cycle epitomizes the raw complexity of nature.


Gene Haynes