Gasteracantha fornicata

The diet of Gasteracantha fornicata is largely consistent with that of other spiders in the genus. This includes small dipterans (flies), small hymenopterans (members of the bee family), Orthoptera, Odonata, and Lepidoptera.[14] The range of prey species does not vary with spider colour. Building a web is the main foraging cost of this species.[9]

Gasteracantha fornicata orients itself and its web to take advantage of light and dark patches in the vegetation.[6] The light and dark bands mimic the environment and serve to attract prey as a part of the colour-as-prey-attraction hypothesis. These spiders effectively utilize their colouration to have the best web visibility and attractiveness within their habitat. Prey typically mistaken the light patches as forager or mating sites, serving as a strategy for Gasteracantha fornicata. This strategy has varying effects on the capture environment of yellow striped spiders versus the white striped spiders. Yellow striped spiders have been found to have the largest number of prey-capture events when it stood in greatest chromatic contrast with the surrounding area (the yellow stripes stand out the most when compared to other colours in the environment). White striped spiders best capture prey when in achromatic contrast with the surrounding area (the brightness of the white stands out the most when compared to the luminescence of the environment).[15] Neither capture rate, prey consumption rate, nor capture success was found to be significantly different between the two morphs.[6][16][17]

The colouration of Gasteracantha fornicata has also been shown to take advantage of prey visual systems of hymenopterans and dipterans. Using an insect colour vision modeling, the white striped version of Gasteracantha fornicata are indistinguishable from sympatric flowers, and the yellow striped version are perceptually indistinguishable from yellow flowers. It has been shown that hiding and covering the distinctive stripes of Gasteracantha fornicata have contributed to diminished prey acquisition.[18]

On its web

Gasteracantha fornicata creates a circular "orb" shaped web, typical of the family Araneidae.[15] Gasteracantha spiders are known to have particularly strong webs compared to other spider species.[11] Like other spiders within the family, Gasteracantha fornicata utilizes a "sit-and-wait" strategy to capture prey. Unlike other "sit-and-wait" predators however, instead of secretive colouration and camouflaging, Gasteracantha fornicata is brightly coloured. This colouration aids spiders in prey capture as a part of the "colour-as-prey-attractant" hypothesis. Spiders with their stark bands are able to attract prey to the web at higher rates compared to spiders that were painted over to conceal their stripes.[6]

Aside from their colouration, members of the Gasteracantha genus frequently display silk tufts as web decoration, placing the tufts along the frame of the web.[10] These lures have been hypothesized to visually attract prey as a "sensory trap";[9] however, presence of web decoration has not been attributed to better feeding success. These decorations also have been hypothesized to serve as a detractor for birds or other predators.[10][19] In non-decorated webs, predators and large animals are more likely to destroy the web, even when the presence of the spider on the web was controlled for.[10] This hypothesis has also been put into question because Gasteracantha build their webs in already sheltered areas in shrubs and rainforest understory, regions that are unlikely to be disrupted by larger predators. While decorations help protect destruction from other creatures, because of the rainforest habitat, webs are frequently rendered ineffective during extended rainstorm periods.[9] In addition, no evidence has found that Gasteracantha fornicata makes assumptions of optimal foraging sites when building their webs.[9][20][21]

The life cycle of Gasteracantha fornicata starts from eggs. The egg sac of Gasteracantha fornicata is made of fluorescent green silk. It measures twelve to fifteen millimeters at its widest point and is shaped as a three-dimensional oval.[12] Gasteracantha fornicata grows through a progressive series of instars. After its series of transitions, its final adult form has a highly sclerotized skeleton and namesake spinal projections. The total body mass and appearance of the spider is subject to change throughout the lifetime. When resources are scarce or when rainfall is low, the spider is found to lose mass and become less vibrant in colour.[9]

A strong sexual dimorphism is present in the males and females of Gasteracantha fornicata. Smaller males (2mm) live on the outskirts of the web compared to females (12mm) and possess a different shape compared to females.[11][22] Whereas sexual cannibalism drives the development of larger males, Gasteracantha spiders do not participate in this practice. To court the female, the small sized male must inconspicuously travel to the female at the center of the orb-web without freezing or being shaken off by female movement. It then mounts the female and copulates. This courtship behaviour is unique to the genus Gasteracantha. Other spiders in the Araneidae family will create a mating thread within the female's central hub where the female will follow vibratory cues to meet the male.[23]

Potential predators of this spider include avians and humans. The webs of Gasteracantha fornicata and other decorated web spiders are described to have anti-predatorial properties, explained by the warning hypothesis. In particular, the conspicuous decorations of the webs of Gasteracantha fornicata' draw larger creature's attention to the web and prevent them from destruction.[6] The fused head and body spikes (cephalothorax region) also serve as a defense mechanism.[4] While the mud dauber wasp Sceliphron laetum solely uses orb-weaving spiders to feed its young, it does not feed the larvae with Gasteracantha because of the particularly hard exoskeleton.[24] The brightly coloured body has been described as a possible aposematic signal, where having bright colouration signals to larger predators not to hunt this spider.[6]

Thermoregulation of Gasteracantha fornicata is related to the amount of sun it gets along the rainforest floor. This sun exposure can be further detailed in the posture the spider takes in the web, the Fabian position. In the Fabian position, the spider is positioned parallel to the direction of sunlight along its longitudinal axis to maximize the level of exposure. Whereas some spiders construct web structures to shade themselves, webs have not shown to serve as a cooling mechanism in Gasteracantha for thermoregulation.[5][27]