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FIGURE 1. Female Banana Spiders (Nephila clavipes) are one of the largest orb-weavers in this country, rivaled in size only by female Black-and-Yellow Garden Spiders (Argiope aurantia). The male Banana Spider is pictured above in the lower left.

   
 

 

FIGURE 2. This view of a female Banana Spider reveals the subtle colors and delicate striping of her abdomen from a ventral (lower) side.

   
 

 

FIGURE 3.Because they are closely related, Banana Spiders (Nephila clavipes) are often confused for Black-and-Yellow Garden Spiders (Argiope aurantia) and vice versa. N. clavipes females can be readily recognized by the presence of distinctive feathery tufts or gaiters on the lower segments of their brown-and orange-banded legs.

   
 

 

FIGURE 4. Banana Spiders prey on a wide variety of medium to small size flying insects including leaf-footed bugs (pictured above) and mosquitoes.

   

Quick Facts

Common Name:

Banana Spider

Other Common Names: Golden Silk Spider, Calico Spider, Giant Wood Spider, Golden Silk Orb Weaver and Writing Spider

Genus / Species:

Nephila clavipes

Size: N. clavipes sexes are highly sexually dimorphic. Females are significantly larger than males. Females 1 to 3 inches (25 to ~~ mm) in length; males about ½ inch (12 mm) in length
Webs: Orb webs average 2+ feet (2 m) in diameter but may range up 3 to 6 feet (1 to 3 m) in diameter. Very complex in design and among the strongest of any species of spiders

Type of Beneficial:

Insect predator

Beneficial Stage(s):

Both adults and immatures are predators

Prey:

Wide range of flying prey small to medium sized flying insects including mosquitoes, bees, butterflies, flies, small moths and wasps

Occurrence:

Widespread (i.e., notably visible) across the county from mid-summer to late fall. Bikers learn to go slow on the first run through a trail during late summer—or volunteer a “point man”!

Look-A-Likes/Confused With: • Nephila clavipes (banana spider) and Argiope aurantia (black-and-yellow argiope spider) are frequently confused. Although color patterns of their abdomens (hind section) vary among individuals, N. clavipes has yellow spots on a muted orange to tan abdomen while A. aurantia exhibits variations of black and yellow colorations.
• The shape of their abdomens (hind section) also differ. The abdomen of a mature N. clavipes female is slender or cylindrical in contrast to the somewhat more rounded and somewhat flattened of a mature A. aurantia female.
• Female banana spiders (N. clavipes) have legs that are banded brown and orange with two feathery tufts or gaiters on the mid-segments of each pair legs except the third pair (we have noticed that the third pair of legs lacks the distinctive feathery tufts or gaiters and is also noticeably shorter).
In contrast, female black-and-yellow argiope spiders (A. aurantia) legs are black, with red or yellow bands on the segments nearest the point of attachment to the body. Each pair of legs contains numerous black spines. Like Banana spiders, the third pair of legs is noticeably shorter.

 

Nephila clavipes is a large size and brightly colored species of the orb-web spider family. Nephila comes from Ancient Greek, meaning “fond of spinning.” Most people call them banana or golden silk spiders, but other common names are calico spider, giant wood spider, golden silk orb weaver and writing spiders. The ‘golden’ refers to the color of the silk, not the color of the spider, for the web of a mature female has yellow threads which look like rich gold in the sunshine.

N. clavipes is the only species of the genus Nephila to be found in the Western Hemisphere. They live in warm regions, from North Carolina and across the Gulf States through Central America, as far south as Argentina, and in the West Indies (found extensively throughout Puerto Rico).

Larger relatives occur in the South Pacific, Southeast Asia and Madagascar. Banana spiders like high humidity and relatively open space. They inhabit forest areas along trails and clearing edges. There are some arboreal or swampy nooks where large numbers of adults and their webs are seen in almost frightening numbers, especially near the coast. Adult males begin to come out in July with most mature females following later, during late-summer to early fall.

Females of N. clavipes are among the largest non-tarantula-like spiders in North America and are one of the largest orb-weavers in this country, rivaled in size only by Argiope aurantia (commonly known as the black-and-yellow garden spider) and Araneus bicentenarius (commonly known as the giant lichen orb weaver).

N. clavipes females are about 3 inches long and their color pattern consists of a silvery carapace (outer body wall) with yellow spots on a muted orange to tan cylindrical body. Her long legs are banded brown and orange with feathery tufts or gaiters on the lower segment, making this spider one of the most easily recognized.

The slender males, on the other hand, are a rather inconspicuous dark brown averaging less than a ½ inch in length and would often go unnoticed if not for the fact that they are often found in the webs of females.

The striking differences between the sexes is known as sexual dimorphism. Sexual dimorphism is when the male and female of the same spider species have physical characteristics so different that they appear not to be the same species. Sexual dimorphism is most obvious when the spiders are mature.

Banana spiders go through many molting stages, but the most notable is the last stage. Approximately 4 days before a female reaches her final molt, she ceases eating and doing any web repair. Around this time, a mature dominant male will move into her web and spend a few days getting to know her. He is waiting for her to finish molting, because the female is only sexually receptive for 48 hours after this last stage has occurred.

When the male approaches a female for copulation, he stimulates her by vibrating his abdomen using a plucking motion. This activity varies depending on the age of the female and the arousal also prevents the male from becoming a meal. However, female predation on males is not a common occurrence in N. clavipes. Interestingly, most female spiders have two independent insemination ducts, both ending in their own sperm storage organ (called spermatheca), but generally only fill one at a time.

Once inseminated, the female spins at least two large (about an inch in diameter) egg sacs on a tree. These sacs consist of hundreds of eggs and are surrounded by a basket of curly yellow silk. Males then occupy a hub position (about two inches above the female) and guard her. Females may change web sites and male partners throughout their adulthood. After the final molt, females can live up to a month, while males live from 2-to-3 weeks. Banana spiders have one generation per year in North America.

The strong web of banana spiders is complex. It is a fine-meshed orb suspended in a maze of non-sticky “barrier webs.” They make big webs, about 3 feet wide, spun in a place best suited to take advantage of the flight paths of other insects. Some scientists suggest that the silk’s color serves a dual purpose: sunlit webs ensnare bees that are attracted to the bright yellow strands and in shady spots, the yellow blends in with background foliage, acting as camouflage.

Typically, the webs are made in open woods or edges of dense forest, usually attached to trees and low shrubs, although they may be in trees tops or between the wires of utility lines. In relation to the ground, webs are woven anywhere from eye-level upwards into a tree canopy.

There may be a rather extensive and haphazard-looking network of guard-strands suspended a few inches across an open space, often decorated with a lumpy string or two of plant debris and insect carcasses clumped with silk. This barrier web functions as an indicator when prey has been caught through vibrations of the web. It is also a kind of early-warning system for spider hunting predators such as birds and damselflies, as well as acting as a shield against windblown leaves. One reference stated the “suspended debris-chain is a clue for birds to avoid blundering into and destroying the web.”

Typically a banana spider first weaves a non-sticky spiral with space for up to 20 more spirals in between. When the coarse weaving is completed, the spider returns and fills in the gaps. Most orb-weaving spiders remove the non-sticky spiral when spinning the sticky spiral, but the banana spider leaves it.

The hub of the web is an asymmetrical orb, located near the top, where the spider waits. This is a semipermanent structure; it is not destroyed. The size and structure of the web indicate the defense strategies and developmental changes these spiders go through. Their webs really annoy hikers and hunters, because during late summer and fall the large golden webs make a sticky trap for the unobservant.

Similar to many weavers of sticky spirals, as the orb ages, it is renewed regularly due to the decline of adhesive properties. When the weather is good (and no rain has damaged the web), the banana spider often rebuilds only a part of it. The spider will remove and consume the portion to be replaced, build new radial elements and then spin the new spirals. This partial orb renewal is distinct from other orb-weaving spiders that usually replace an entire web.

Once prey is entangled in the web, banana spiders wrap it in a silk-like cocoon. Nephila species then bring their prey back to the hub of the web rather than leaving it in situ (i.e., where it was entrapped and wrapped). Some researchers believe this is a preventative action to reduce the amount of food stolen by kleptoparasites such as Argyrodes.

The banana spider preys on a wide variety of small to medium sized flying insects, which include mosquitoes, grasshoppers, stinkbugs, leaf-footed bugs, bees, butterflies, flies, small moths and wasps. Banana spiders have even been seen feeding on beetles and dragonflies. These spiders are rarely found in row crops, because of lack of web support, but they are one of the two most common orb-weavers in citrus and pecan groves. Oddly, some banana spiders are reported to display an almost manic fear of cockroaches. It is thought the cockroach’s fast movements and large, dark shape cause some of the species to run from or ignore a perfectly good meal.

Banana spiders are really wonderful creatures. Their dragline thread (the silk) is of particular benefit to us as they weave strong webs compared to some other spiders. Currently, there are tests being done on their silk as it surpasses the strength of “Kevlar,” a fiber used in bulletproof vests.

The dragline thread is biodegradable, stronger than steel (with a tensile strength of 4 ×109 N/m, exceeding that of steel by a factor of six) and is economically valuable. Recently, the silk has been used to help in mammalian neuronal regeneration for the body’s immune system does not recognized it and the silk has antibacterial properties.

Did you know that nine golden orb weavers from Australia perished in the Space Shuttle Columbia disaster? The “AstroSpider” experiment is part of an international program (STARS) that encourages students to design experiments for flight on the US Space Shuttle or International Space Station.

A while back, there were the efforts to produce garments from Nephila silk. The spiders were somehow fastened while spinning and the extruding thread was coiled up. This went on until the spider was exhausted. Fortunately, it did not prove commercially viable.

There are fishermen on the coasts of the Indo-Pacific Ocean who remove Nephila webs and form them into a ball, which is thrown into the water. There it unfolds and is used to catch baitfish. On a lighter note, natives in the South Pacific eat the pregnant females as a protein supplement, relishing them either raw or roasted. Different reports state the consistency is similar to a mix of raw potato and lettuce, or that it has a nutty flavor like peanut butter but stickier.

Lastly, in the film Twelve Monkeys, Jed Cole (Bruce Willis’ character), is incarcerated in a mental hospital located in Baltimore, Maryland. He catches and swallows what appears to be a banana spider, or a very similar species. The film makers got it wrong as Baltimore is well outside the known range of Nephila in the U.S.

Because of its size, people sometimes assume that the banana spider is dangerous to people. In reality, it is a shy spider (as nearly all spiders are). Just know this species is considered medically harmless to humans. There is little danger to a healthy adult from an encounter with the banana spider. It will only bite if held or pinched and the bite itself will produce a localized pain with a slight redness, which quickly goes away. On the whole, the bite is much less severe than a bee string. It is best avoided, but it won’t kill you.

Yes, it may require a certain amount of time for most humans to take a liking to spiders—or at least to reduce their level of disgust or fear. However, if you ever have an occasion to witness some of their beneficial works—especially when you come across one of their large webs filled with the carcasses of Texas-sized mosquitoes and other small biting flyers—you’re likely to develop a new found admiration and appreciation of N. clavipes, the banana spider!

Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.

 

This web site is maintained by Master Gardener Laura Bellmore, under the direction of William M. Johnson, Ph.D., County Extension Agent-Horticulture & Master Gardener Program Coordinator.

All digital photographs are the property of  the Galveston County Master Gardener Association, Inc. (GCMGA) © 2002-2006 GCMGA - All Rights Reserved.