Taxonomy
The upper body surface of female Ixodes ricinus is only partly covered by the scutum. The gnathosoma (hypostome, palps and chelicerae) is large and clearly visible. The depression at the end of the first leg is a Haller’s organ.
Photo credit: Peter York, NHM
Morphology
Ixodes ricinus is a tick (order Ixodida) because it has:
- backwardly-pointing teeth on the hypostome
- a Haller’s organ on the terminal segment (tarsus) of the front legs -each organ comprises a pit and capsule containing hair-like sensory structures (setae)
- the external respiratory openings (spiracles) are located on a pair of spiracular plates
It is a hard tick (family Ixodidae) because:
- the gnathosoma (the mouthparts) – comprising the hypostome, palps and chelicerae - is large and clearly visible from above in all life stages
- the upper body surface is partly (larva, nymph, female) or completely (male) covered by a hardened shield (scutum)
The anal groove arching in front of the anus is only seen in the genus Ixodes.
Adult specific character states are:
- the female scutum is almost circular
- the basal segment (coxa) of the first pair of legs (legs I) has a long, slender internal spur
- all leg coxae have a small external spur
- the tarsi of legs I taper towards their apex
- the female genital aperture is between leg coxae IV
Look-alikes
Ixodes hexagonus Leach – the hedgehog tick - has a similar distribution to I.ricinus and parasitizes many of the same host species.
It can be easily identified by the hump near the apex of tarsus I (absent in I.ricinus), the female genital aperture being between coxae III and not IV, and the rounded hexagonal, rather than circular, scutum.