Fertilization

During fertilization, the female’s projecting sternum interacts with the male’s clypeus specifically during sperm transfer, indicating that, rather than having a stridulatory purpose, the female’s sternum instead plays a role in sexual selection. This interaction may allow the female to exert some level of control over the copulatory actions of the male, since contact has been observed specifically when the male exerts genital pressure on the female during sperm transfer. The projecting sternum may act as a mating filter and selective pressure on the males, allowing only those males who are still able to transfer sperm despite the physical constraint of the sternum.^[5] Females tend to mate multiple times, and the second male has a higher likelihood of reproductive success, fertilizing 65-82% of the female’s eggs.^[9]

Once fertilized, the female carries the egg sac in her fangs while waiting for the spiderlings to hatch.^[1] Females do not feed during this time and instead devote their energy to guarding the egg sac from predators.^[8]

Brood size

Each brood contains approximately fifty spiderlings.^[8] In addition, although it is difficult to follow individuals in the field due to web migration, females occasionally produce multiple clutches over their lifetime, sometimes as soon as two months after the successful hatching of the first brood.^[6]

Molting

During development, spiderlings normally undergo five molts, with females more likely to undergo a sixth molt than males and poorly fed individuals more likely to undergo a sixth molt than well-fed individuals.^[6]

Lifespan

Although the lifespan of H. pluchei has been difficult to track due to web migration, individuals raised in the lab can have a lifespan of up to one year.^[8] Males’ lifespan in a natural habitat is often terminated prematurely by various environmental conditions, so a faster rate of development for males often yields a higher rate of reproductive success.^[6]

Stridulations

Unlike in many other species of spiders, both males and females of H. pluchei possess stridulatory organs, with the females possessing comparatively thicker pedipalp segments. Stridulations in males of many spider species play a role in courtship, and although H. pluchei female stridulations also play a role in courtship, they may indicate aggressive or preventative behavior. When females copulate with males immediately and willingly, they do not stridulate. Stridulation only occurs in cases where the female is less receptive towards the male’s advances, often leading to an unsuccessful mating attempt by the male.^[3] Females can also regulate mate choice through their sternum projections, which serve as filters by limiting male success during sperm transfer.^[5]

Male/female feeding interactions

Although other species in the family Pholcidae exhibit “chivalrous” behavior, in which the male will step aside to cede prey to the female or wrap up the prey and bring it to her, this behavior does not occur in H. pluchei. In contrast, males of H. pluchei often enter females’ webs for the purpose of aggressively stealing food. In competitive interactions over prey, males tend to lose interactions only when they are smaller than their competitor. This, as well as a lack of wrapping or exchanging of the prey, indicates a lack of chivalrous behavior on the part of the male.  For males in other species of Pholcidae, chivalrous behavior may induce a female to mate, thereby increasing the male’s reproductive success. Since the first male that mates with the female H. pluchei is unlikely to be the one to fertilize her eggs, there may not be as great of an advantage to engaging in chivalrous behavior.^[9]

Group living

Spiderlings can choose to join a group web or build their own web, with the majority of individuals choosing to live in a group.  They make this decision when they are 4–5 days old.  Each strategy has its own costs and benefits, as group living decreases the amount of food allocated to each spider but also decreases the amount of silk each spider must produce, benefitting individuals by demanding less energy expenditure. Although spiders in groups tend to have smaller abdomens than those living alone, indicating lower foraging success,^[10] spiders live in groups more often than would be predicted by chance. This may be due to the high energetic cost of producing silk and increased amount of silk needed to build a web alone as opposed to within a group. An individual's decision to build its own web or join a group web is based on its level of recent feeding success.^[2]

H. pluchei spiderlings co-inhabiting a web do not cooperate in other realms, such as prey capture or wrapping remainders of prey in silk, and instead engage in display and fighting behaviors as they compete for prey, with larger spiders tending to win these fights. These conflicts can sometimes escalate to death, especially when the spiders are of similar sizes. Spiders in the same web will occasionally cooperate on wrapping prey, but only when the prey is very large. This cooperation may only occur because the spiders cannot see each other and are therefore unaware of each other’s presence.^[2]

Predators

Holocnemus pluchei are preyed upon by jumping spiders of the family Salticidae, including Portia fimbriata and Portia labiata. In response to invasions from other species, H. pluchei will “bounce,” or move their legs rapidly up and down while remaining grounded on the web in an attempt to dislodge the intruder.^[11] Invading species employ aggressive mimicry tactics when invading the webs of H. pluchei and are often able to avoid setting off the resident’s “bouncing” strategy, enabling these web invaders to successfully capture their prey.^[12]