Tick Morphology

Deer tick - Scott Bauer

Hard ticks

• Hard, chitinous covering over dorsal surface called the scutum
  • Unique to hard ticks
  • Males have a scutum which covers the entire body surface
  • Females have a scutum which only covers a small area behind the head

• Prominent biting mouthparts

• Festoons ('pie crust edging') around the posterior body margins

• Enamel coloured patches on scutum are present on ornate ticks

• Female hard ticks may swell up to 3 times their normal size when taking a blood meal

Soft ticks

• No scutum

• Mouthparts are not visible from dorsal surface

• Feed little and often as cannot swell as much as hard ticks

Mouthparts

• Sensory organs for locating a feeding site called palps

• Chelicerae for puncturing the skin

• The hypostome pushes through the wound made by the chelicerae where backwards pointing teeth lock the mouthparts into the skin
  • Dorsal groove in the hypostome permits the flow of tick saliva and host blood

Feeding

Engorged Ixodes scapularis - Thomas Hedden

• Ticks stand upright

• Chelicerae cut through skin creating a pool of blood

• Hypostome is inserted deep into the skin

• Mouthparts are cemented into place

• Ticks feed continuously

• Tick saliva flows into host and contains
  • Histamine blocking agents to minimise the host inflammatory response
  • Anticoagulants to ensure the free flow of blood
  • Cytolysins to enlarge the feeding lesion
  • Vasoactive mediators, enterases and carbohydrate splitting enzymes to increase the vascular permeability, facilitating feeding
  • Paralytic toxins

• Host tissue is broken down leaving a zone of necrosis creating a feeding lesion