N. clavipes females are among the largest non-tarantula-like spiders in North America and are perhaps the largest orb-weavers in this country, rivaled in size only by Argiope aurantia (Fabricius) and the largest Araneus species, including A. bicentenarius (McCook). Females range from 24 mm to 40 mm in length. The female color pattern, consisting of silvery carapace, yellow spots on a dull orange to tan cylindrical body, brown and orange banded legs, plus the hair brushes (gaiters) on the tibial segment of legs, I, II, and IV, make this spider one of the most easily recognized. The males, on the other hand, are rather inconspicuous dark brown, slender spiders averaging 6 mm in length which would often go unnoticed if not for the fact that they are often found in the webs of females. [1]

Life History, Habits, and Habitat:

N. clavipes in temperate North America has one generation per year under field conditions. Adult males are present from July to September, with most females maturing in August. Mature females are found late into the fall, when they make at least two large eggsacs 2.5 to 3 cm in diameter consisting of several hundred eggs surrounded by a basket of curly yellow silk. Populations in the tropical parts of the range probably produce more eggsacs, as the related N. maculata (Fabricius) averaged nearly nine eggsacs per female in New Guinea (Robinson and Robinson 1973a). The life history of N. clavipes has not been studied through all the instars, but it is probably quite similar to N. maculata (Robinson and Robinson 1976), with one or two fewer instars.

The finely meshed, large web of N. clavipes (often 1 to 2 meters in diameter) is placed to best exploit insect flight paths (i.e., above the herbaceous stratum). In tropical America, webs are found most frequently at edges of forest clearings, alongside forest trails, and across forest watercourses (Robinson and Mirick 1971). The hub of the web where the spider waits is located near the top of the web, making an asymmetrical orb. Kaston (1972) gives an illustration of a portion of a web in detail. The web is a semi permanent structure, i.e., it is not destroyed and created periodically as is the case with many members of the similar family Araneidae. Large portions of the web may be repaired leaving the remainder undisturbed (Peters 1955). Occasionally stabilimenta (bands of zigzag silk) are incorporated into complete webs of immatures, and more frequently are found on skeleton webs (webs lacking viscid spiral) made by immatures and used as molting platforms (Robinson and Robinson 1973b).

Prey-capture behavior by Nephila species is considered primitive compared to species of Argiope and Eriophora. The large species in these latter genera make webs nearly as large as those of Nephila, yet the mesh of these webs are coarse when compared to those of Nephila. N. clavipes capture smaller prey on the average than do, for example, Argiope argentata (Fabricius) or Eriophora fuliginea (C.L. Koch) webs of similar size. However, due to their use of immobilization wrapping as a primary attack weapon (Robinson 1969, Robinson and Olazarri 1971, Robinson et al. 1969), Argiope and Eriophora species are able to capture larger prey on the average than do Nephila species which directly employ biting to subdue the prey. Differences in web mesh size and attack behaviors between the two types of orb-weavers can be viewed as an evolutionary advancement by these other large orb-weavers to reduce competition for prey with Nephila.

Webs of Nephila species, as well as of other large orb-weavers, are liable to kleptoparasitism by small (3 to 4 mm) silvery spiders of the genus Argyrodes Simon (family Theridiidae). Robinson and Robinson (1976) recorded as many as 30 of these kleptoparasites in a single web of N. maculata, and we have seen over 40 Argyrodes in an abandoned N. clavipes web. This latter observation was noteworthy, since Robinson and Robinson (1976) demonstrated that Nephila species could reduce the kleptoparasitic load by periodically moving their webs even if the web site was productive of prey. One aspect of prey capture by Nephila species, that of always bringing the prey back to the hub rather than leaving wrapped prey in situ, has been hypothesized to be a preventative action to reduce the amount of food stolen by Argyrodes, since detection of the theft action of the kleptoparasites would be difficult on such a large web (Robinson and Robinson 1973a).

Another problem faced by golden silk spiders in tropical and subtropical climates is overheating. Special behaviors and body features have evolved in Nephila to protect against the problem. The silvery carapace reflects sunlight, while the long, cylindrical body may be pointed directly at the sun, thus reducing the area of exposed body surface. Force evaporative cooling may be employed by manipulating a drop of fluid with the chelicerae. Cooling responses generally occur above 35°C (Krakauer 1972). The web does not have to be perpendicular to the sun in order for the spider to employ orientation; in fact, webs are generally placed so as to capture the most insects regardless of the sun's position, and the spider's orientation movements can be quite complex (Robinson and Robinson 1974). [1]