Jewel spider, Christmas spider
Austracantha is a genus of spider with a single species, Austracantha minax, commonly known as the jewel spider or the Christmas spider. It is a member of the family Araneidae (the orb-weavers) and is endemic to Australia. They are relatively small spiders, reaching a maximum total body length of only around 12 mm (0.47 in) for females, and 5 mm (0.20 in) for males. Their abdomen has six distinctive projections ("spines") that makes them easy to identify. They are predominantly a shiny black, with variable white, yellow, and orange patterns. Melanistic forms also occur during autumn. They are facultatively gregarious, and can be found in large aggregations of overlapping orb webs. They feed on small flying insects that get entangled in their webs. They are harmless to humans, though the webs can be a nuisance for bushwalkers. They are most abundant during the summer months.
Jewel spiders have a distinctive appearance that makes them relatively easy to identify. The cephalothorax is black in colour with a bluish metallic sheen. It is covered with small white hairs (setae). The carapace (upper part of the cephalothorax) is rectangular in shape. The sternum (chest) is brownish black, with a yellow central area. The chelicerae (fangs) are black with four to six small teeth. The maxillae and other mouthparts are black at the base, lightening to brown and bright yellow at the tips. The pedipalps are dark brown.
Jewel spiders have eight eyes arranged in two rows. The front row is recurved, with the two middle eyes (anterior median eyes) further in front than the two at the sides (anterior lateral eyes). The back row is procurved, with the two middle eyes (posterior median eyes) further in the back than the two at the sides (posterior lateral eyes). The legs in females are predominantly dirty yellow to orange in colour. Black tips are present on the last three segments of the legs (the tibiae, metatarsi, and tarsi). The first pair of legs are longer than the others. In males, the legs are mostly black, with brownish tips.
The opisthosoma (abdomen) is large, slightly wider than it is long, and strongly rounded at the front and back. It is shiny black with bright colourful patterns. These colours can vary, but they are usually white, yellow, or yellow-orange. Its most distinctive feature are the three pairs of large "spines" projecting outwards. The first two pairs on the front are close to each other, forming a V-shape as they point to the sides. They are short and roughly conical. The spines on the rear are longer and point backwards. There are wide spaces between them and the two front pairs. The spines are black or brownish black from above, but has a yellow-orange to rusty red lower surfaces.
Jewel spiders are sexually dimorphic. Females are about twice as large as males, reaching 7 to 12 mm (0.28 to 0.47 in) in total length. Their carapace (upper part of cephalothorax) is squarish, usually around 2.7 to 3 mm (0.11 to 0.12 in) long and 2.5 to 3 mm (0.10 to 0.12 in) wide.
Males are usually only around 3 to 5 mm (0.12 to 0.20 in). The carapace is slightly rectangular, usually around 2.1 mm (0.08 in) long and 1.8 mm (0.07 in) wide They are also less colourful than females; with predominantly dark reddish brown bodies. The spines are blunt and are much shorter than the spines of the females. Like all mature male spiders, they are relatively easy to identify because of their greatly enlarged pedipalps used in sperm transfer during mating.
Jewel spiders exhibit colour polymorphism. They can be found in white, yellow, or red colour morphs. Jewel spiders found later in autumn (from March to April) are also sometimes melanistic, being entirely dark brown to black in colouration. It is believed that the appearance of these colour morphs are triggered by environmental factors, rather than by genetics. For example, it has been speculated that the purpose of the melanistic colour morphs may be to facilitate better heat absorption during the colder months.
Jewel spiders are endemic to Australia. They can be found all throughout the mainland, as well surrounding islands, including Tasmania, Barrow Island (Western Australia), and the Montebello Islands. They are more common on the southern regions of the continent, from southern Queensland and New South Wales, through Victoria and Southern Australia, to Western Australia. Though they can be found in the Northern Territory, they are less common and their place is usually taken by species from the genus Gasteracantha instead.
Jewel spiders are opportunistic predators. They prey on small flying insects like flies and mosquitoes that get entangled on their webs.
After locating a receptive female, male jewel spiders will begin courtship by first attaching a "mating thread" from nearby plants to the edge of the female's orb web. It then positions itself in the middle of this thread and begins strumming it with their first and second pair of legs. The female will respond by moving towards the source of the vibrations, eventually climbing unto the mating thread itself. Once this happens, the male will wrap its legs around the female tightly and insert its pedipalps into the female's epigyne, transferring its spermatophores (silk packets containing sperm) into the female's spermathecae.
A female jewel spider can mate with multiple males during a single reproductive cycle. If given the chance, the female will still readily mate with other males shortly after a successful mating. To prevent sperm competition, the successful male will defend the female shortly before and after mating. It actively drives away other rival males until the female enters a refractory period and ceases to be receptive to further matings. This usually happens an hour to a day after a successful mating, during which the female will herself aggressively attack and drive away all courting males.
Females usually attach their egg sacs on vegetation and other surfaces near the edges of their webs (including grass blades, leaves, and twigs). They are usually bound longitudinally with loose lengths of silk, but they can sometimes be found dangling. The egg sacs are around 15 to 35 mm (0.59 to 1.38 in) in length and can vary in shape from circular to pointed at both ends. They are reddish brown to golden brown in colour, though rarely they may also be bright yellow. They are made from closely woven silk.
The spiderlings overwinter within the egg sacs until early spring. Females reach sexual maturity at around the middle of January, while males mature earlier in the middle of December.
