• Arachnids
• Ticks
• Mites

• Insects
• Lice
• Fleas

Ectoparasites are divided into two main groups, arachnids and insects, classified by structural characteristics. The arachnid class includes ticks and mites. The insect class consists of lice, fleas and grubs.

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 of the species.

Arachnids

Ticks
Ticks thrive on blood obtained from the host. They are subdivided into hard and soft ticks according to structural characteristics.

• 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 in 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 to bottom, can expand to several times its original size as the 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 according to whether their life cycle involves one, two or three hosts. This is described under the section on life cycles.
  
• Soft Ticks
  Soft ticks differ from hard ticks in several respects. They have a leathery outer skin rather than a hard cuticle, and both males and females engorge when feeding on the host. Their shapes vary among species. There is no scutum, and the capitulum is located on the bottom side of the tick near the its front. Otobius megnini, the spinose ear tick, is a soft tick. Only larvae and nymphs of this species are parasitic. Adults live in hidden areas in the environment, such as within cracks in the wood of barns.

Mites

Mites are arachnids that can be seen clearly only with a microscope. Their bodies are usually round and flattened. Mites eat normal skin debris, such as scales. An alternate feeding habit in some species is puncturing the skin to suck lymph fluid. Notoedres cati 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. Otodectes cynotis, the ear mite, can cause great irritation in the ears of cats and other carnivores.

Insects

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 biting louse, Felicola subrostrata, feeds on the skin and skin debris with mouth parts adapted for chewing.

Fleas

Fleas can be very annoying to cats. Both dogs and cats are infected by the species Ctenocephalides felis and Ctenocephalides canis. Some cats develop severe skin reactions to flea bites. Flea bite dermatitis can be difficult to treat. Fleas have bodes which are flattened side to side, and powerful legs adapted for leaping.

Taenia

Go to Life Cycles