Ticks have long been recognised as annoying parasites of domestic animals. In 355 BC Aristotle described them as 'disgusting parasitic animals', and there are few today who would disagree with this sentiment.
Ticks are blood feeding ectoparasites, closely related to mites and more distantly related to spiders and scorpions. They are not insects, they are arachnids. Ticks feed on a large variety of hosts including mammals, birds, reptiles and occasionally amphibians. Many British species are specialist wildlife parasites faithful to their specific hosts and as such have either a limited or patchy distribution. The life cycle of Ixodid ticks involves four stages: the egg stage and three parasitic stages, larva, nymph and adult.
From left to right Ixodes ricinus larva, nymph,
adult male, adult female (all unfed)
Globally ticks are one of the most important disease vectors, second only to mosquitoes, in terms of the number of pathogens vectored. After feeding on an infected host, a tick can become infected and consequently transmit this infection to any subsequent hosts that it may feed on. Many species of tick remain infected for the duration of their life span, maintaining infection from one stage to the next (trans-stadial transmission) with some infected females ticks also transmitting infection to their offspring via their eggs (trans-ovarial transmission).
In Britain, Ixodes ricinus is the most commonly encountered tick species, often found in woodland, particularly deciduous or mixed woodland, rough upland or moorland pastures, heathland and grasslands. Ticks are particularly abundant in ecotones, the transition zone between two vegetation communities, such as woodland and meadow or shrub communities, which permit a wider range of potential hosts. Vegetation cover and leaf litter at ground level offer protection from adverse temperatures, humidity, and from predators. Thus, removal of ground cover exposes ticks to high temperatures and hinders their ability to maintain water balance and avoid desiccation during questing (host seeking).
Typical Ixodes ricinus habitat
In Britain Ixodes ricinus activity has been recorded sporadically at all times of the year, although generally larvae begin questing in spring or early summer (April/May), peaking in activity between June and August and declining in September. Nymphs are active from February through to October, activity peaking in May/June, with a smaller second peak between September and November. Adult activity is similar to that observed in nymphs, occurring between February and September, with a peak in June.
Active ticks quest by clinging to vegetation at a height where they are most likely to encounter the host animal appropriate to their life stage. They detect passing animals by holding out their front legs where their sensory Haller’s organ is located; this sensory gland being acutely responsive to changes in carbon dioxide, heat, odour and physical disturbances.
Ticks quest until they either successfully attach to a host or have lost excessive amounts of water when they retreat to ground level where they will recover and later quest again. Ticks will die if they are unsuccessful in finding and attaching to a host before their energy reserves are used up.
A questing Dermacentor reticulatus female
Ixodes ricinus is the main disease vector in Britain capable of transmitting the following pathogens:
Ixodes hexagonus is a known vector of Borrelia burgdorferi sensu lato in parts of Britain. Ixodes trianguliceps is also considered to be a capable vector of Anaplasma phagocytophilum in Britain.
For further information on the above diseases please visit the specific pages on the HPA website accessible via the A-Z index: http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ
Effective self protective measures include:
Actual size of the Ixodes ricinus nymph
Last reviewed: 24 August 2012