By Bill Conroy BSc. Agr. (Syd)
In the temperate Eastern Coastal Zone of Australia, the great majority of attacks by ticks on humans and their companion animals result from the feeding activity of one species the shell-back or Paralysis Tick Ixodes holocyclus.
Mature females of this species lay large numbers of eggs (up to 3,500) in leaf and branch litter, under the scaly or fibrous bark of certain trees and shrubs, or in dense fine foliage near the tips of branches. They wax the eggs to give a cohesive mass and attach these at the selected site.
The eggs hatch to give a tiny larval tick, six-legged like an insect, which is the first in a three stage lifecycle. These larvae (6 legs) known by the common names seed tick, grass tick or shower tick can be very numerous in late summer to mid autumn. The two later stages are the nymph sometimes called "bush tick" which is prevalent from late Autumn to early Spring, particularly during warm sunny breaks in winter, and the adult, with separate male and female forms, labelled shell-back or paralysis tick. The nymphs and adults are eight-legged like a spider.
See also the lifecycle image and the geographical distribution map for Ixodes holocyclus.
Each phase in the life cycle needs to engorge with red blood before a resting period, leading to metamorphosis to the next stage. The male adults have rudimentary mouth parts and do not feed. The females, after insemination, must engorge in their turn in order to mature their egg mass for the next generation. Animal red blood is the sole food of the species.
After hatching
or metamorphosis a powerful instinct drives the unfed ticks upwards along the
trunks of trees and shrubs until they find a suitable lateral branch, move out
to the tip of this and begin questing for a blood yielding prey. In certain
types of very humid weather ticks will move out across grassy areas and attach
to the feet or lower legs of their target.
The forepart of a tick's head and its mouth parts are modified into a suction tube with a set of implements at its end designed for breaking up surface skin and absorbing blood from the exposed capillaries. To stimulate blood flow before applying suction pressure, the tick injects saliva, containing powerful chemicals which have toxic effects, ranging from extremely irritating and debilitating rashes, to fever with aches and pains, ulcers and glandular swellings and in extreme cases respiratory arrest and other forms of life threatening reactions.
Ixodes holocyclus is a very vigorous and versatile parasite deriving its blood supply, as needed, from a wide range of hosts including most avians, every kind of native and exotic mammal, both feral and domestic and a range of reptiles. It is therefore very likely to be a distributive agent for infectious diseases of humans, entering the body through the circulatory system and having alternative hosts among the animal population, both domesticated and free-living. Tick typhus or tick spotted fever caused by a bacteria in the same group as those which cause New Guinea Scrub Typhus and Rocky Mountain Spotted Fever, is the most prominent tick-borne disease in certain coastal and sub-coastal suburbs of the Greater Sydney Region and generally in tick infested areas of the temperate East Coast. It can cause acute illness.
Another disease with many similarities to Lyme disease, caused by ticks in North America and Europe, is occurring in increasing numbers of cases in the same areas.
In all cases where unusual symptoms occur following tick-bite, the patient should see a doctor practising in a tick-infested locality or otherwise familiar with the parasite and its effects.
Larval ticks often attack in large numbers, causing extensive extremely irritable rashes which can cover the whole body. They are best dealt with by soaking for 1/2 hour in a bath with 1 cup of sodium bicarbonate to a full bath at appropriate temperature. Removal of individual larvae is unnecessary. Nymphal and adult ticks usually attack singly or in small clusters and should be physically removed with fine point forceps or a patented tick remover. Unlike most insects and spiders, the thoracic and abdominal parts of a tick's body are unified, with the internal organs enclosed in a single sector of carapace. The whole of this becomes a sack of blood as the tick engorges. It is most important therefore that the tick should be firmly grasped by the 'head' and withdrawn with a single continuous pull. Revulsive substances such as turpentine, ti-tree oil, and alcohol should not be used as, along with physical pressure they can cause regurgitation of the tick's stomach contents into the victim's blood-stream. For all stages take every care to avoid breaking up the tick.
In tick-infested areas most people are bitten in their own homes or gardens, when crossing street verges, bushwalking or at outdoor recreation sites. Preventive practices relating to clothing, pet care and garden management are most important.
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| ^ Ixodes holocyclus male | ^ Ixodes holocylus female |
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| ^ Ixodes holocylus female (engorged) |