Northern golden orb weaver, Giant golden orb weaver
Nephila pilipes (northern golden orb weaver or giant golden orb weaver) is a species of golden orb-web spider. It resides all over countries in East and Southeast Asia as well as Oceania. It is commonly found in primary and secondary forests and gardens. Females are large and grow to a body size of 30–50 mm (overall size up to 20 cm), with males growing to 5–6 mm. It is the second largest of the orb-weaving spiders apart from the recently discovered Nephila komaci. The first, second, and fourth pairs of legs of juvenile females have dense hairy brushes, but these brushes disappear as the spider matures.
The N. pilipes golden web is vertical with a fine irregular mesh. It is not symmetrical, with the hub usually nearer the top. Rather than egg sacs being hung in the web, a pit is dug which is then covered with plant debris or soil.
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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Not a migrantAnimals that do not make seasonal movements and stay in their native home ranges all year round are called not migrants or residents.
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starts withN. pilipes display female gigantism and male dwarfism (see Sexual dimorphism section). In terrestrial animals, N. pilipes have the most size differences between males and females. This can be explained by the evolutionary selection for females with better fecundity. Female N. pilipes have huge parental investments to their progenies, including egg production and web construction (see Parental care section).
N. pilipes prefers moist habitats with no direct sunlight. It can be found in Japan, China, Vietnam, Cambodia, Taiwan, Malaysia, Singapore, Myanmar, Indonesia, Thailand, Laos, Philippines, Sri Lanka, India, Nepal, Papua New Guinea, and Australia. In Australia, most N. pilipes are found in rainforest habitats in northern and eastern Australia, where climate is humid and vegetation offers shade against direct sunlight. In general, N. pilipes are distributed along coastal lines, where precipitation is ample. However, reports show that N. pilipes can be found in dry sclerophyll and low shrublands, hundred miles away from the coast. N. pilipes can survive in many climate types, including temperate coastal, Mediterranean, subtropical and tropical savannah climates. They construct webs in bushes and trees, near surface water, and against buildings and other terrain structures. To reduce heat from the sun, like other spiders, Nephila spp. has a thermoregulatory behavior. Experiments show that when the temperature reaches 32 °C, Nephila spp. will adjust the angle between its body and the incoming sunlight, orienting its abdomen towards the sun but keeping the cephalothorax parallel to the web. When temperature further rises, it will align the full body along the sunlight direction, further reducing the area that is receiving heat from the sun. At temperature above 40 °C, Nephila spp. will abandon the web. Unlike other relatives, the distribution of N. pilipes doesn't depend on seasons. Adult females are active throughout four seasons and continuously lay eggs. Adult males are present in the population for longer times than females.
Nephila spp. prey upon only a few species. Nephila spp. will remove some specific insects from their webs. They avoid vespid wasps, alate ants, and other insects that secrete distasteful compounds. Due to Nephila’s large body size, it can prey on insects with a broad size range, from 2 mm to even larger size than themselves. They adopt different strategies for different sizes of preys. Small preys are directly caught and removed from the web. For larger ones, they inject venom and wait for the decease of their prey. However, Nephila spp. have a dramatic change in predation style from the spiderling to adulthood. During the spiderling stage, they feed collectively on a common web. Upon reaching adulthood, they construct their own webs. Nephila spp. also reserve food caches to deal with periods of food shortage. They wrap surplus prey in silk and store them in the hub of the web. The silk covering can significantly reduce water loss due to evaporation. Food cache can reduce weight loss during periods with limited preys.
It has been reported that some N. pilipes can adjust the ultraviolet radiation reflected by stripes on their body to attract preys that are UV light oriented. The bands on the legs and body of N. pilipes can reflect UV radiation, so they are more visible to flying insects. The contrast of colors makes them look like food sources for insects, rather than a predator spider.
Upon reaching adulthood, males leave their webs and begin the search for females. They look for the correct web chemical compositions and web characteristics. It is reported that N. pilipes do not have an airborne pheromone-based signaling system for mating.
In nature, sexual conflicts between males and females are very frequent because males and females have very different reproduction purposes. Males have relatively less parental investment than females, so their goal is to fertilize as many females as possible. Females, on the other hand, tend to be reluctant to mate repeatedly and only select those males with good genes. Female spiders can display aggressiveness in a variety of ways: shake the web and chase the male when approaching; kick the male when the male makes contact with the female's leg; violently shake body when the male climbs up the female's dorsum; abruptly interrupt mating by kick the male off. Unlike other close relatives, N. pilipes have a less aggressive mating ritual, and sexual cannibalism is very rare. Males have evolved a mechanism called mate binding to avoid females' resistance and cannibalism. Males can deposit silks soaked with sexual hormones onto the female's body to calm the tactile and chemical receptors. In this way, males can reduce cannibalism and maximize the number of females they fertilize.
