- Ticks - Classification
- Class :
- Arachnidae
- Order :
- Acarina
Definition
Ticks are acarians, of which 850 species are known worldwide. They are divided into 3 families: Ixodidae or "hard ticks", Argasidae or "soft ticks" and Nuttalliellidae, a family that is in between the other two. Ticks are blood-suckers, and therefore potential vectors of diseases.
Morphology
Ticks belong to the order acarina. Their unsegmented bodies include 2 parts, called the capitulum (at the front) and the idiosoma (at the rear). They have a soft, extensible cuticle; hard ticks also have a dorsal plate called the scutum. They have 4 pairs of legs with claws.
The capitulum contains the mouth parts, including chelicerae, which are used to pierce and cut the host's skin, and a hypostome to anchor the tick to the host. The olfactory receptors located on the first pair of legs as well as the hairs and receptors of the mouth parts allow the tick to find its way and locate its target.
Life cycle
The development cycle of ticks takes place in 3 stages: a larva is born from the egg and attaches to a vertebrate animal, takes its blood meal, drops from the animal and moults into a pupa, which does the same and moults into an adult tick. After copulation, the female lays approximately 1,000 to 20,000 eggs (hard ticks) or 20 to 150 eggs (soft ticks). The duration of a cycle is 2 to 4 years on average, and may range up to 7 years if climate conditions are not favourable.
Some ticks live in an open environment - such ticks are called "exophilic" (mainly hard ticks) - while others prefer a sheltered environment (tunnels, caves, tree bark, etc.) and are called "endophilic". Certain ticks inhabit both. They are found in the forest, woods, high grasses, public parks, and so forth. Ticks are seasonally active, from spring to autumn. Specifically, they are active in temperatures between 7 and 25°C (the warm hours of the day).
Feeding habits
Ticks are hematophagous, which means that they feed on blood. Certain ticks can only bite one type of host, while others target many different hosts. For example: R.sanguineus bites dogs, Ixodes ricinus bites large mammals, rodents and birds.
Ticks also have varying affinity for humans. Ticks locate their targets using their sensory receptors (found on the legs and the capitulum). They are sensitive to carbon dioxide, ammonia, phenols, odours released by the body, as well as vibrations (the vibrations created by footsteps, for example), body temperature, etc.
There are 2 strategies for finding a host:
- the strategy of waiting : they climb up on vegetation and wait for a host to pass, with the forelegs lifted, prepared to latch on. elles grimpent sur la végétation et attendent le passage d’un hôte, les pattes avant relevées, prêtes à s’accrocher.
- the strategy of attack : when ticks come out of their habitat and seek a host.
Bites
After latching onto its host, the tick moves around on the animal to find an area rich in blood vessels. Once it has found this, it cuts the skin using its chelicerae, and then anchors its hipostome, which will allow it to remain attached for a long time.
The bite includes 2 phases:
- a slow phase in which there is little ingestion of blood.
- a much faster phase, in which it greatly increases its weight.
At the same time as it is drawing blood, the tick injects several substances that facilitate its blood meal, making the bite painless and preventing the host from defending itself. The blood meal last between 2 and 15 days in hard ticks, while in soft ticks it lasts about 1 to 2 hours.
During the bite, the tick may inject pathogenic agents along with the other substances.