Australia: The Land Where Time Began
Fauna of the Mulga Country
Social insects are very abundant in mulga-land. Ant and termite colonies can be seen as storage organs for the community, buffering the production pulses. The dominance of these invertebrates anchors the food web, supporting a network of other invertebrates and vertebrates.
The barking Spider Selenocosmia stirlingi
They are common in the mulga country north of Alice Springs, their circular holes being the size of a camera lens cap. The spider is large and hairy, covering the palm of the hand, not that many would want one on their hand. They hide in the hole, lunging out at prey that walk on the fan of web spread in front of the hole. It is one of the largest and most aggressive of the desert spiders. It is a mygalomorph, or mouse-like spider. It is one of the few spiders that habitually forages, at least partially. The burrows of barking spiders are often clustered in the litter zone around trees because this is the place where insects are most common.
There are 17 desert mygalomorphs, trap door spiders and funnel web spiders. They are all opportunistic feeders. Many are almost exclusively ant and termite feeders. The larger ones feed on beetles and the occasional vertebrate. Apart from the barking spider, the mygalomorphs remain in their holes with the front legs resting on the rim of the burrow. Some extend the fan of web around their burrow entrance by twig-lining, adding pieces of litter, such as mulga phyllodes, to the silk, then wait like holding a fishing line.
Barking spiders are not necessarily safe in their burrows. Stripe-faced dunnarts sometime fight a spider, then if they win they eat the spider and move into its burrow.
For desert spiders the greatest hazard is sheet flooding. The Aganippi, trap door spiders, avoid the flood water by having tightly fitting lids that fit into a groove around the rim of the burrow. Other types of spider build structures to deflect the flood water from their open burrows. Female trapdoor spiders live for at least 20 years, and take 2 years to reach sexual maturity. The males live only until they find a mate, then having mated, die. The eggs are laid in a cocoon and kept in the burrow, the spiderlings remaining in the burrow for about a year. During this tine time the female fasts, which is why she only breeds every 2 years. Most trapdoor spider young disperse by running out of the burrow, but some disperse by climbing to a high point, such as a blade of grass or a bush, then streaming out a long line of silk that is picked up by the wind that carries them, often great distances, before depositing them again. Mating and dispersal of young occur after rain, when the ground is damp and so easier to dig a burrow.
Stripe-faced dunnart Smithopsis macroura.
This nocturnal insectivore is one of about 5 dasyurids (carnivorous marsupials) living in mulga country. They mainly live in spinifex grassland.
There are many lizards in mulga country, Gilberts Dragon (Lophognathus gilberti), geckoes, Rhynchoedura ornata) and Diplodactylis stenodactylus, 2 skinks Ctenotus leonhardii and C. schomburgkii. Ctenotus leonhardii apparently has a special liking for spiders, though it does eat insects.
The larvae of the moth Chlenias inkata is abundant in spring on the mulga phyllodes. They have the habit of dropping on silk threads at the slightest disturbance, even a hand clap, and dangling for up to 15 minutes before climbing back up the thread. They pupate in the ground, and have been known to take up to 3 years to emerge from the pupa.
The Gryllacridid ('gryll', cricket-like, 'acris', grasshopper-like)
This cricket is a ferocious predator. Their anatomy is about half way between crickets and grasshoppers. It is believed there about 200 species in Australia. As with lizards, some plants and many other invertebrates, their greatest radiation occurred in Australia's arid zone. They live under the bark of mulga and other trees, and burrow in sand, and like trapdoor spiders, often build a lid for their burrow. At least one is known to block the entrance to its burrow with a pebble that it holds tightly in place with silk.
Many insectivorous birds are present in the mulga in spring when the moth larvae are abundant. There are nectar feeders such as the White-fronted Honeyeaters are plentiful in the flowering season. In this infertile habitat the bird fauna is similar to that in the more fertile places, such as the desert foothills and floodouts. Some larger birds not found in these other habitats are the Black-faced Cuckoo-shrike and the Grey-crowned Babbler. The pied butcher bird of the more fertile habitats is replaced by the smaller grey butcher bird. Some birds that are common in mulga are the western Gerygone, Slaty-back Thprnbill and Chestnut-rumped Thornbill, Variagated Fairy Wren, Chiming Wedgebill - named from its call of the whistled chime of 4-6 notes - and the White-browed Treecreeper. The Mulga Parrot and Burkes Parrot feed on seeds in the grass understorey.
Penny Van Oosterzee, 1993, The Centre - The Natural history of Australia's Desert Regions, Reed Australia.
|Author: M.H.Monroe Email: email@example.com Sources & Further reading|