Ixodes holocyclus, commonly known as the Australian paralysis tick, is one of about 75 species in the Australian tick fauna and is considered the most medically important. It can cause paralysis by injecting neurotoxins into its host. It is usually found in a 20-kilometre wide band following the eastern coastline of Australia. Within that range, Ixodes holocyclus is the tick most frequently encountered by humans and their pets. Because the same area includes Australia's most densely populated regions, bites on people, pets and livestock are relatively common.
Paralysis ticks are found in many types of habitat, particularly areas of high rainfall such as wet sclerophyll forest and temperate rainforest. The natural hosts for the paralysis tick include koalas, bandicoots, possums and kangaroos.
The use of common names has led to many colloquial expressions for Ixodes holocyclus. The most generally accepted name is Australian paralysis tick or simply paralysis tick. The following table gives some of the other names used to describe various stages of Ixodes holocyclus.Many of these common names, such as dog tick or bush tick, are best not used for Ixodes holocyclus because they are also used for some of the other ticks found in Australia.
Te
TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
Ov
OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
I
starts withIxodes holocyclus is found mainly along coastal eastern Australia, from near Cooktown in far north Queensland to Lakes Entrance in Victoria. In places, it is found more than 100 km inland, particularly in areas of moist escarpments and ranges such as the Bunya Mountains of Queensland and the Lower Blue Mountains of New South Wales.
The distribution map gives only an approximation of the tick's distribution as the situation is not static. There are reports from inland Victoria, including north-eastern suburbs of Melbourne. This may reflect general movement of insects and ticks from equatorial to polar latitudes which in turn may be related to climate change.
The need for humid conditions largely determines the botanical niche of this species. Low, leafy vegetation provides higher humidity levels by reducing the desiccating effects of wind and direct sunlight. This environment also suits the tick's major host, the bandicoot, as it seeks out grubs and worms in the leaf litter. Certain vegetation may be conducive to paralysis ticks.
There are mixed reports about whether paralysis ticks climb trees. Some references mention ticks climbing to the tops of trees, while others report that they stay within 50 cm of the ground.
The life cycle of Ixodes holocyclus consists of four stages: egg, larva, nymph, adult. Ixodes holocyclus requires three hosts to complete its life cycle, thus it is a "three-host tick". Ticks hatch as six-legged larvae after an incubation period of 40 to 60 days. Larvae search for a blood meal from a host, feed for four to six days, then drop from the host and moult to become an eight-legged nymph. Nymphs require a second blood meal before they can moult again to become an adult. Female adults then require a further blood meal of up to ten days before dropping off to lay up to 3000 eggs in leaf litter. Male adults will search for females on the host for mating, and to parasitise the females for blood meals. That life cycle takes around a year to complete, with minimum being 135 days, and the maximum 437 days.
To find a host, ticks "quest", climbing onto vegetation and waving forelegs slowly until a host comes within reach. When on the host, they may not attack immediately, but wander for up to two hours until attaching on the back of the host's head or behind an ear. Certain chemicals, such as carbon dioxide (hence the use of "dry ice" baits), as well as heat and movement, serve as stimuli during the questing behaviour.
Both female and male ticks quest for a host, but for different reasons. The female quests for a blood meal, the male to search the host for a female tick in order to mate and feed from her. Males may parasitise female ticks by piercing their cuticles with their mouth parts to feed on the haemolymph, and up to four males have been found feeding on one female tick. Adult male ticks rarely blood-feed on a host. The outside surface, or cuticle, of hard ticks grows to accommodate the large volume of blood ingested, which, in adult ticks, may be anywhere from 200 to 600 times their unfed body weight. When a tick is fully engorged it is said to be replete.
