The arachnid class of ectoparasites includes ticks and mites. An arachnid has only two body segments: a fused head and thorax, and an abdomen. It has four pairs of legs as an adult, and no wings or antennae.

The life cycle of arachnids involves incomplete metamorphosis: the eggs hatch into nymphs which at least superficially resemble adults. On the other hand, complete metamorphosis is seen in insects, in which the immature forms are totally unlike the adults.

Ticks

Ticks thrive on blood obtained from the host. The common swine ticks are members of the family lxodidae, or hard ticks.

The bodies of hard ticks are roughly oval in shape and pointed at the front. The anterior segment is a false head, or capitulum; the shape of its base is characteristic of the particular tick genus. Structures on the capitulum may also help to identify the tick genus. Palps are segmented structures used for probing the host. The hypostome anchors the tick to the host's skin, and mouthparts on the capitulum are adapted for sucking blood.

The abdomen, flattened top and bottom can expand to several times its original size as a tick feeds on its host. This phenomenon, referred to as engorgement, is seen only in females. One part of the skin, the scutum, located on the back of the tick, does not expand during engorgement. In some species, the scutum may be decorated with coloured pigments. These patterns of pigmentation may help with identification. Male ticks are generally more colourful than females in ornate (coloured) species. The presence or absence of other structures may also help to identify ticks.

A further classification of hard ticks is made based on whether their life cycle involves one, two, or three hosts. This is described under the section on life cycles.

Mites

Mites are arachnids that can be seen clearly only with a microscope. Their bodies are usually round and flattened, although an exception to this general rule is Demodex, which is cigar-shaped. Mites eat normal skin debris, such as scales. An alternate feeding habit in some species is puncturing the skin to suck lymph fluid. Sarcoptes scabiei mites actually burrow tunnels into the skin where they live, feeding and depositing eggs. Larvae that hatch may create side tunnels or leave the area and migrate to undamaged skin to burrow new tunnels. Demodex mites, the cause of demodectic mange, live in hair follicles and the associated skin glands.

Louse infestation in ear		Mite		Louse

 

Insects are characterised by having three distinct body parts: head, thorax, and abdomen. Wings may or may not be present. Insects have one pair of antennae on the head and three pairs of legs on the thorax. Many insect parasites - including some species of flies, mosquitoes, bugs, and fleas - spend little time on the host. In contrast, other insects, including lice, remain on the bodies of hosts for their entire life cycles.

Lice

Lice are wingless, flattened insects with six legs adapted for clinging to hair. The swine louse (Haematopinus suis) has mouth parts adapted for puncturing skin and sucking blood.