Christmas Jewel Spider

Appearance

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. The carapace is rectangular in shape. The sternum is brownish black, with a yellow central area. The chelicerae 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 further in front than the two at the sides. The back row is procurved, with the two middle eyes further in the back than the two at the sides. The legs in females are predominantly dirty yellow to orange in color. Black tips are present on the last three segments of the legs. The first pair of legs are longer than the others. In males, the legs are mostly black, with brownish tips.

The opisthosoma 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 in total length. Their carapace is squarish, usually around 2.7 to 3 mm long and 2.5 to 3 mm wide.

Males are usually only around 3 to 5 mm. The carapace is slightly rectangular, usually around 2.1 mm long and 1.8 mm 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 are also sometimes melanistic, being entirely dark brown to black in coloration. 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.

Distribution

Jewel spiders are endemic to Australia. They can be found all throughout the mainland, as well surrounding islands, including Tasmania, Barrow Island, 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.

Reproduction

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 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. 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 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.

Food

Jewel spiders are opportunistic predators. They prey on small flying insects like flies and mosquitoes that get entangled on their webs.