Archaeocroton sphenodonti
The tuatara tick is arguably more endangered than the tuatara it parasitises (it is classified as a ‘relict’ species under the most recent NZ Threat Classification) as it is only found on four of the 12 island groups where tuatara are found. Tuatara ticks, which feed exclusively on tuatara blood, are often lost, or even deliberately removed, when tuatara are translocated (ticks are not usually considered to have high conservation value). But just as tuatara represent a unique lineage of reptiles, tuatara ticks represent a unique lineage of reptile ticks. This is a really nice example of parasite evolution tracking the evolution of their hosts. The biology and ecology of tuatara ticks is at least as fascinating as that of tuatara. Remarkably, they can survive for up to a year without a host to feed on! Despite that, their fate is ultimately intrinsically linked to that of their hosts, and without the charismatic appeal of tuatara, it can be hard to persuade people of their value, but these ticks are truly amazing wonders of nature and marvels of evolution.
Although it only has one host species, the tuatara tick is a ‘three-host’ tick. The tuatara tick feeds on the blood of tuatara during each of its three lifecycle stages – larva, nymph and adult – and in between each stage, the tick drops off their host into the environment and moults. At the adult stage, males and females find each other on their reptilian host, mate, and then the female engorges and detaches into the environment, where she lays eggs. When tuatara ticks are in the environment phase of their lifecycle, they cannot feed, and must undergo extensive fasting periods while they wait for another host. The ability of ticks to fast is unrivaled in the animal kingdom – with some species able to go without food for up to 6 years!
As far as we know, the tuatara tick doesn’t cause significant harm to its host; tuatara that have very high tick loads (as many as 500 ticks have been counted on a single tuatara!) may experience small reductions in body condition over time, but otherwise they appear to coexist with their host well. While the population on Takapourewa|Stephens Island represents the largest tuatara tick population, other island populations of tuatara also support tick populations. In addition, tuatara ticks have been successfully translocated with their hosts to new mainland sanctuaries, including Zealandia (Wellington) and Orokonui (Dunedin).
The tuatara tick has an interesting taxonomic past that has only recently been resolved by Barker et al (2018), who reclassified the tuatara tick into a new genus – Archaeocroton, with ‘archaeo’ meaning ancient/old, and ‘croton’ meaning tick. So, this further confirms the tuatara tick – just like its host – is the sole representative of a probably ancient lineage of ticks.
Check these links for more info on the Tuatara Tick in NZ
Wikipedia: Information on Archaeocroton
iNaturalist observations: Archaeocroton sphenodonti
Radio NZ: Tuatara Tick Critter of the Week
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