Tick Alert Group Support Incorporated

Lifecycle & Ecology of the Australian Paralysis Tick (Ixodes holocyclus)

• Lifecycle
• Hosts
• Predators
• Distribution (separate page)

Lifecycle

Ticks are arachnids, in the same animal class as spiders, scorpions and mites. Their mouth parts are specialised to pierce the flesh of host animals and draw blood. The length of the life cycle is variable, depending on the weather and the availability of hosts.

In south-eastern Australia the development of Paralysis Tick from egg to adult may take a year, but variations in temperature and moisture can hasten or delay development at any stage. See Distribution.

The life cycle is comprised of four stages- egg, larva, nymph, adult. Larvae have 3 pairs of legs and the nymphs and adults 4 pairs. The Australian Paralysis Tick requires three hosts to complete its life cycle, thus it is a three-host tick. To moult to the next stage a blood meal must be obtained by the larva or nymph. Moulting is known as ecdysis. 

The process of seeking a host is known as questing - each tick climbs to the top of nearest vegetation and extends or waves its forelegs to and fro in order to make contact with a prospective passing host. Certain chemicals such as carbon dioxide (hence the use of "dry ice" baits) as well as heat and movement serve as stimuli for 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 the female ticks by piercing their cuticle with their mouth parts to feed on the haemolymph (up to 3-4 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 actually grows to accommodate the large volume of blood ingested, which, in adult ticks, may be anywhere from 200-600 times their unfed body weight (Sonenshine, 1991). When a tick is fully engorged it is said to be replete.

Stage	Image	Early Development	Engorgement	Late Development	Notes
Egg		A small fraction of eggs survive and hatch to larvae after 49-110 days incubation. Development occurs with suitable warmth and high humidity (eg moist leaf litter).	n/a	n/a	The eggs can survive the winter.
Larva		Larvae, also known as a seed ticks, emerge from the eggs and move towards lateral branches, and across grassy areas during humid weather in order to attach to their prey. Larvae  undergo 7-44 days of hardening and then climb vegetation (eg the tips of leaves). They attach to a passing host.	Larvae feed for 4-6 days then drop to ground.	Over a further 19-41 day period larvae then moult to become nymphs.	The overall period in the larval stage (hatch to moult) is temperature dependent. It may, for example, take 20 days at 27.5 ° C and 40 days at room temperature (21 °C) but may extend to 36 weeks. Larvae are just visible to the naked eye. Under laboratory conditions unfed larvae may survive for 162 days.
Nymph		Nymphs are very active and 5-6 days (up to 31 days) after moulting attach to another host.	Nymphs feed for 4-7 days, then drop to the ground.	After a further 3-11 weeks the nymphs moult to become adult males or females.	Again the period is temperature dependent. may emerge from the nymphal stage from the 20 days at 24-27 °C to 53-65 days at 10-21 °C. Dry conditions also prolong this period and can actually kill nymph. Under laboratory conditions unfed nymphs can survive for 275 days
Adult Female		The newly moulted adult female becomes increasingly active for the 1st 6-7 days and seeks a host. It attaches to the final host after 7-9 (up to 77) days. After insemination by a male tick (sometimes before) a female feeds on blood in order gain the nutrients for the egg mass to mature.	Adult female engorges for a period of 6-30 days, the time being dependent on weather- slower when cold. The 30 day engorgement time is derived from laboratory culture colonies. Under natural conditions, the time taken for an adult female to engorge while on the host varies from 6 to 21 days, the period being longest in cool weather. When fully engorged (replete), the adult female drops off the host to the ground.	After 11-20 days the gravid female starts to lay a batch of 2,000 to 6,000 eggs (20-200 eggs per day) into moist vegetation (leaf and branch litter, under the bark of trees and shrubs, or in foliage near the tips of branches) over 16-34 days. The eggs are attached as a mass with a wax-like substance to the site. The female tick dies 1-2 days after egg laying is complete.	Thus a dog may carry a tick for up to three weeks without the tick being significantly engorged or causing paralysis. However in warm weather the female engorges rapidly, and at the same time, injects her toxin into the host thus causing paralysis if the host is susceptible. The adult female does not usually inject detectable amounts of toxin until the 3rd or 4th day of attachment to the host, with peak amounts being injected on days 5 and 6. Under laboratory conditions, female ticks have been kept alive for more than two years.
Adult Male		The newly moulted male seeks a host. Male ticks do not engorge rather they wander over the host searching for unfertilised females with which to mate.	Male tick does not engorge on the host.	The male dies after fertilising the female although some males can endure for longer if they parasitise the engorging female.

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Hosts

Common hosts include long nosed bandicoot (Parameles nasuta), giant brindle bandicoot (Isoodon torosus), echidnas and possums. Potential hosts include many species of mammals, birds and occasionally reptiles. Because of continuous infestation the native animals are usually immune to tick toxins.

Most mammals such as calves, sheep, goats, foals, pigs, cats, cavies, rats, mice and man can be infested by the Australian Paralysis Tick. Fatalities resulting from a single engorged adult female tick are mostly reported in the young animals of the larger species and all ages and sizes of the pet species (dogs and cats). Larvae and nymphs can also produce toxic reactions in the host. Fifty larvae or five nymphs will kill a 40 g rat, larger numbers of either can induce paralysis in dogs and cats. One adult female can kill four different susceptible rats during engorgement. Although it is not typical, an engorging adult female apparently can reattach several times to different dogs (Jones, 1991).

Predators