Zygiella x-notata, sometimes known as the missing sector orb weaver or the silver-sided sector spider,Factsheet 6: Missing-sector Orbweaver (Zygiella x-notata) , British Arachnological Society, 2016. Retrieved 27 November 2016 is a spider species in the family Araneidae. They are solitary spiders, residing in daily spun orb webs. Z. x-notata is a member of the genus Zygiella, the orb-weaving spiders. The adult female is easily recognized by the characteristic leaf-like mark on her posterior opisthosoma, caudal to the yellow-brown cephalothorax.
The webs of Zygiella x-notata spiders are known for their characteristic missing sector, lending to the common name of spider as the "missing sector orb weaver." This species is distributed widely around the world, primarily inhabiting areas of human occupancy in northern Europe.
Common prey include flying insects and other small insects. These get caught in the sticky spiral hub of the spider's orb web. Capture of prey occurs as the foreleg of Z. x-notata detects vibrations on the signal strand that connects the spider's retreat to the prey-capturing hub of the web. Webs are rebuilt daily by juvenile Zygiella x-notata and are renewed as needed by adult females. After sexual maturity, males discontinue web production in search of fecund females. After reproduction during the summer months, males die. Females produce an egg sac in late autumn and juveniles emerge in late spring. After several moults, juvenile females are ready to reproduce.
Description
The adult female Zygiella x-notata has a body size of 5-11mm in length, while adult males have a body size up to 7mm. In adult females, the carapace width is 1.5 mm. The dorsal tibia of the walking legs and pedipalps contain a group of trichobothria. There is only one sensillum on the leg metatarsus. The prosoma is yellow-brown, with a leaf-like mark on the opisthosoma. The abdomen has a silvery sheen due to guanine crystals below the skin. Adult females are recognizable from their grey banded legs and pattern of dark grey waves on their dorsal side. Adult males are smaller than adult females, and display a dark dorsal exterior with dark brown legs and cephalothorax. The male abdomen is smaller and less marked with a shiny cream color than the female abdomen. In moderate climate, adults appear from July to October, sometimes even into December. In warmer regions, Z. x-notata is active all year.
Common names The common name missing sector orb weaver comes from the distinctive structure of Z. x-notata's web. Characteristically, this species is known to build a web with a missing sector containing solely a signal thread in the top half. The species has also been referred to commonly as the silver-sided sector spider.
Taxonomy Zygiella x-notata was named by Clerck in 1757, as Araneus x-notatus.World Spider Catalog The taxonomic status of the species is still considered valid.
The specific name x-notata is Latin for "having been marked with an x".
Habitat and distribution Habitat Zygiella x-notata is common in areas inhabited by humans, including on boats and docks. They are also found on urban vegetation like bushes or shrubs. Females construct an orb-web preferentially near human settlements, and this is where they live out their adult lives.
Zygiella x-notata has been discovered on cliffs and bushes in Britain and across Europe.
Distribution This species of orb-weaving spider natively inhabits areas of Europe, and is invasive in some coastal areas of the Americas. They can also be found in some other locations around the world. Zygiella x-notata is abundant in the west Palearctic region, and is also distributed across the Holarctic. Primarily, Z. x-notata is widespread across much of Britain, as well as Western and Central Europe. They are also common in New Zealand and are occasionally found in South Africa, Mexico Colombia, Ecuador, Panama and Honduras.
Web aggregations As urban colonizers, Zygiella x-notata often aggregate around human settlements. Ideal locations for web building include constructions such as walls, fences, and window frames, as these provide sufficient anchors for urban web development. Because these spaces are in high demand as optimal web building sites, they are often inhabited by multiple individual Zygiella x-notata spiders, where each individual builds and resided in their own web in close proximity with other individuals. Despite their characterization as solitary spiders, the species aggregate up to 25 individual spiders per square meter near human constructions.
Diet Feeding Juvenile zygiella x-notata characteristically build a new web each day until they reach adulthood. Adult Zygiella x-notata spin orb-webs which are used to capture and incapacitate prey. Rather than building a new web every day as juveniles do, adult female Z. x-notata build an initial web and renew it nearly every day as needed. The female spider will sit in her retreat on the web, which is attached to a signal strand in the characteristic missing orb-web sector. When prey are caught in the web, the female can thus detect its presence through vibrations in the signal strand. As these vibrations are detected, she climbs down the silken signal thread to the hub of the web where the prey has been trapped. Prey type is dependent on the spider's native habitat and geographical location, but usually consists of flying prey such as Diptera. Male Zygiella x-notata feed similarly to females as juveniles, but once they reach adulthood they no longer build webs in order to capture prey, rather focusing on successful reproduction.
Predatory feeding behavior There are four stages of predatory behavior in Zygiella x-notata as described by Venner et al.: first, the "waiting phase" occurs, in which the spider is immobile in its retreat in the top corner of the web. A foreleg rests on the signal thread that spans from the spider's retreat to the hub of the web. Second is a "detection phase", where after prey has come into contact with the web, the spider moves toward it down the signal thread. Third is a "capture phase" in which the prey is incapacitated by the spider and subsequently moved back toward the retreat. Zygiella x-notata has been observed to bite and wrap its prey with silk during this phase as a means of incapacitation, prior to transportation to the retreat. Finally, there is an "ingestion phase" where the spider eats the prey in its retreat and removes the prey's remains from the web.
Vibratory signals in prey capture Zygiella x-notata spiders have the capacity to detect vibratory signals in both the air and via web vibrations. When building an orb-web to initiate the prey-capture behavior, female Zygiella x-notata can detect the presence of potential prey through air-borne vibrations. This stimulates web-spinning behaviors, even prior to prey capture. Once vibratory signals are detected, female spiders engage in one of several potential behavioral response patterns: 1) at least one leg is slightly moved; 2) the spider's front legs are repeatedly lifted off the signal thread; or 3) the spider walks out of its retreat and scurries down the signal thread to the hub of the web. In a characteristic and repeatable series of events, the spider exits the hub, rushing in the direction of the source of the initial vibratory signal. Once the spider has found the source of the vibration, it touches the prey with its first pair of legs. The spider then grabs the prey using its first three pairs of legs, and bites it. Consequently, if no further vibrations (either threadborne or airborne) are detected once the spider has entered the hub of the web, Z. x-notata will actively vibrate the web to detect motionless dead prey or dirt particles hanging in the web. This "web-jerking" procedure, occurring through flexes in the spider's forelegs in contact with the web radii, is repeated until the spider finds a prey item in the web by following the anomalous vibration.
Web
Web type Zygiella x-notata spiders build an orb web in areas frequently occupied by humans. The orb web has a spiral-like appearance with radii converging to a central hub. During the early construction of the web, a nonsticky spiral is formed to later be replaced with a sticky spiral. Characteristic of the species, a "missing sector" is often present in the top half of the web that is crossed by a signal thread connecting the hub of the web to the spider's retreat. The signal thread is variable in length, reaching anywhere from 4 cm to 50 cm long.
Effects of prey on web-building The predatory feeding behavior of the missing sector orb weaver influences changes in web construction. Web building was found to be stimulated by the presence of prey, resulting in spiders in the presence of prey to spin their webs earlier than spiders in the absence of prey. However, web building duration decreased in the presence of prey and thus web sizes were found to be smaller across the sample population. These characteristically smaller webs are spun with narrower web meshing, aiding in the quick capture of prey. Although these webs were smaller than webs built in the absence of prey, they provided a quick method to trap prey. This exemplifies Zygiella x-notata'''s capacity to sense changes in local prey availability. A similar study conducted by Venner et al. found that this species of orb weaving spiders changes its web building behavior in response to new information detected during prey capture. When the spiders experienced the act of capturing and consuming prey, they adapted their web construction and energy expenditure in anticipation of the next capture.
Web construction Web construction occurs through an observable and repeatable process that becomes more organized with increasingly identical webs as the adult female spider ages. According to Anotaux et al. there are four steps to the process of web construction. First, the spider constructs an outer frame and radial threads. Second, she produces an auxiliary spiral. Third, she builds a sticky capture spiral meant to trap local prey. Finally, she remodels the center of the web – the hub – which connects to the signal thread as a prey detection device for the spider which lay in wait in her retreat.
Web longevity Juvenile Z. x-notata spiders have been found to rebuild their webs daily in order to catch prey. Web renewal typically occur at the end of the night for both juvenile and adult spiders. Generally, the longevity of Zygiella x-notata webs is approximately one day.
Influence of aging and experience on web construction Multiple studies have shown that the composition and construction frequency of Zygiella x-notata orb webs change with increasing age and experience in the resident female. Anotaux et al. determined that older Z. x-notata spiders invest less silk in the production of their webs as compared to younger spiders in both short- and long-lived varieties. Older adult female spiders were also found to have greater variation in their orb webs than younger adult females, reflecting a decline in locomotor functioning correlated with increased web irregularity in older age. Venner et al. established a correlation between prey capture and ingestion, and web rebuilding practices among adult female Z. x-notata. Spiders who engaged in the four stages of predatory behavior and subsequently rebuilt their webs were found to invest less in the capture area of their newly built web.
Web anomalies