Number of mates

Trichonephila clavipes female in center and male top left.

T. clavipes males may mate just once, monogynously, but are also capable of polygynous mating.^[9] In many web-building spider species, including those of the Nephila genus, male spiders are only able to mate once due to behaviors such as sexual cannibalism and genital mutilation during copulation. These spiders thus display monogynous mating systems. Unusually, however, males of T. clavipes rarely face sexual cannibalism or genital mutilation, and are thus able to mate multiply. Monogyny can still occur for many male individuals, though, due to factors like ability to encounter female webs and ability to compete successfully with other males. Another, less conspicuous factor contributing to monogyny is that like many spider species, T. clavipes males produce a limited amount of sperm over their lifetimes.^[10] Thus, sometimes a male will only have enough sperm for a single mating, forcing the male to invest in a monogynous relationship rather than searching for further mates.

There are several factors that play into a male's total mate number, but the ability of T. clavipes males to mate multiply allows males of all sizes to have equivalent mating success. It is thought that as a result, there is relaxed selection on male size in T. clavipes and other similar species.^[9]

Male sperm limitation

T. clavipes males have a limited amount of sperm available to them throughout their lifetimes and can therefore only inseminate a few females at most before they die.^[10] Multiple mating success is dependent on the first female they choose to mate with: when males mate with virgin, newly molted females, they completely deplete their sperm supply, whereas when they mate with older, non-virgin females, they are able to retain some of their sperm for future matings. Additionally, males may still engage in mating behavior even when they do not have any sperm to give to the female, although the mating behavior is markedly less vigorous.^[10] This inability of a male to inseminate further females may explain why male T. clavipes who have mated with virgin females will often remain on the female's web and guard her, rather than leave the web to search for future mates.

Mating success with virgin vs. non-virgin females

Mating with virgin females can be seen as a high-risk, high-reward situation for males of the species.^[9] In situations where male T. clavipes are limited to monogyny in their environment, mating with virgin females offers the most reproductive payoff. Hence, a male using up his entire sperm reserves mating with a virgin makes sense; it allows the male to maximize his potential reproductive success with that single female. However, T. clavipes females do vary in mate quality, and virgin females happen to be the most active during a time period when a female's risk of mortality before she lays her fertilized eggs is highest. Thus, mating once with a virgin female and never mating again, although offering higher potential payoffs, also poses greater risks and a high variability in reproductive success. In fact, mating multiply with two or more non-virgin females is usually just as successful for males as mating monogynously with a virgin female, and given that the risks associated with non-virgin female mating are lower, it is likely that T. clavipes males prefer polygyny over monogyny.^[9]

Mate guarding

Mate guarding by T. clavipes males is size-dependent.^[9] Because smaller males are less successful at physically competing with other males, they must invest much more time into successfully mating with a female on her web. As a result, it benefits the male more to search for a new web, rather than to spend even more time on the current web guarding the female with whom he has just mated. Conversely, larger males have a higher chance of winning access to a female at a new web and can thus afford to spend time engaging in mate guarding before searching for a new partner. The trade-off is that increased mate guarding generally results in a lower mate number, so males perceive a benefit in a higher mate number, guarding rates will generally decrease.^[9]

Size is just one factor that influences male guarding behavior. Other factors like choice of a virgin female mate and sperm depletion can also make guarding behavior more likely, since the male cannot engage in further matings and no longer experiences a trade-off between guarding and mate searching.^[10]

Silk glands

There are seven different types of silk glands across the orb-weaving spider species, each producing its own type of silk, and T. clavipes females possess all seven of these silk glands.^[4] The glands are: (i) major ampullate, (ii) minor ampullate, (iii) piriform, (iv) aciniform, (v) tubuliform, (vi) flagelliform, and (vii) aggregate. The major ampullate silk shows high tensile strength and is thus used in structures that require stability, such as draglines, bridgelines, and the radii of webs. Minor ampullate silk is used as scaffolding during the web-building process, while piriform silk is used like cement, bonding fibers to each other and other structures. Aciniform silk is also strong, like major ampullate silk, but is flexible as well, allowing it to be used for wrapping prey and insulating egg cases. Tubuliform silk forms the tough outer shell of egg cases, and the flagelliform and aggregate silks are used in prey capture for their extensibility and stickiness. These silks differ in the specific spider fibroin, or "spidroin," proteins that comprise them.^[4]

A single thread of the anchor silk has a tensile strength of 4×10⁹ N/m², which exceeds that of steel by a factor of eight (ultimate strength of steel 500x10⁶ N/m²). Research at Iowa State University has shown that T. clavipes silk, specifically in the draglines, has exceptionally high thermal conductivity, exceeding that of most metals.^[13]