ACARI | Ixodida (ticks)

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I think it would be fair to assume that most people who live or spend time in the countryside will have some knowledge of ticks. Obviously, they can be encountered in other habitats, but contact is far more likely in rural locations, particularly in rough grassland areas or along woodland tracks and, if you work or regularly walk in this type of environment, it's almost a given that you'll pick up the odd tick from time to time. The likelihood is also increased if you have a pet, especially a dog or cat, as they are particularly prone to being bitten, so even if you haven't found a tick on yourself it's quite likely that you've had to extract one at some point.

The chance of contact increases in the spring as this is when they're at their most active and, if the conditions are right, the increase in numbers at this time of year can be very noticeable. I've often found them on my arms, or even on my legs or lower body even though I always wear long trousers when I'm out. If you keep to the paths, you may well avoid them, but if you start lingering near low-growing vegetation or, if you're like me, and are regularly kneeling or even laying down taking photos, then it's pretty much inevitable that you'll become more intimately acquainted. The important thing is to be aware that you could pick up a tick and to know how to recognise one as it's not always obvious once they're imbedded.

Although the chances of actually contracting Lyme borreliosis are very low as only a small percentage of ticks are likely to be infected with the spirochaetes bacteria that cause the disease there has, quite naturally, been plenty of publicity about the risk and the possible effects if not detected and treated at an early stage. Understandably this has resulted in the general view that ticks are bad news; worthless disease carriers that should be exterminated and, consequently, the idea that anyone might actually enjoy photographing them borders on madness!

Possibly so, but despite their reputation and the fact they're not true members of the soil mesofauna community like mites, they are classified in the Acari and need to be covered.

Ixodes ricinus - nymph

Ixodes ricinus - adult female (questing)

As this is effectively a one species section, I've utilised the space to include a fair bit of information about their lifecycle as there are some interesting aspects that are not common knowledge. However, before we go into too much detail it's worth taking a step back to understand what a tick actually is and to have an indication of the species that could be encountered.

A simple description would be that ticks are blood-sucking ectoparasites of various vertebrate species - primarily mammals, but also birds and, in some countries, reptiles and amphibians. Most species are generally host specific, or at least have a small range of hosts, whereas others are opportunist feeders that are far less specific. In either case they need blood to complete their lifecycle. They are placed in the taxonomic order Ixodida, which sits alongside Mesostigmata in the Acari Parasitiformes division.

Excluding the occasional occurrence of a non-listed variety that may have accidently arrived via the pet trade, there are currently 24 known species of tick that could be found in Britain. They are separated into two distinct families, Argasidae

and Ixodidae, respectively known as 'soft ticks' and 'hard ticks'.

It's unlikely that you'll come across a 'soft tick' by chance as there are only four established species in the UK, two in the genus Argas which are associated with pigeons or seabirds, and two Carios species that are parasites of bats.

The Ixodidae comprises four genera, Dermacentor and Haemaphysalis each with a single species, Hyalomma with two species, and the primary genus Ixodes with sixteen species. However, once you start looking at the ecology and distribution records it soon becomes apparent that apart from the common and widespread Ixodes ricinus (deer tick) as featured here, there are very few that you're likely to find.

For example, Dermacentor reticulatus (meadow tick) which is mainly associated with farm animals is only likely to be found

in South West England or West Wales; Haemaphysalis punctata (red sheep tick) which has similar hosts, as well as rabbits and humans, has only been officially recorded from South East England and the west coast of Wales; Hyalomma aegyptium (tortoise tick) is very rare; and Hyalomma marginatum (bont-legged tick) is only known from migratory birds and has only been recorded in the larvae and nymph forms.

The situation with the Ixodes species is much the same as many species have very specific hosts, such as voles in the case of Ixodes apronophorus (marsh tick), or various seabirds as with Ixodes unicavatus (cormorant tick) and Ixodes uriae (seabird tick). Many of the others are only occasionally recorded and when you analyse the remainder there are probably only three species that need to be considered. If I owned a dog, I'd ensure I knew how to recognise Ixodes canisurga (dog tick) especially if it is regularly kennelled as this particular tick is relatively common in that type of accommodation as it has a hard cuticle that withstands the dry conditions. They may also bite cats, but as far as I'm aware the likelihood is minimal so, from a personal point of view, taking account of where I live and the fact that I'm not going to be actively looking for ticks, I'm probably only going to find two species, Ixodes ricinus and possibly Ixodes hexagonus.

Ixodes ricinus - adult male (questing)

Ixodes ricinus - freshly moulted nymph

Ixodes ricinus is the most widespread species in Britain and across Europe. It is also the most studied tick as it's a vector

of a wide-range of pathogens that cause various diseases in both animals and humans. Although the species is commonly known as the 'deer tick' especially in forest areas or indeed any area where deer are present, such as the Royal Parks, it is probably better, or certainly more widely known as the 'sheep tick' as it's responsible for a number of sheep-related diseases and significant mortality in lambs. It is also responsible for red-water fever in cattle and can infect dogs with various diseases. Other animals may also become infected and, of course, humans could contract Lyme disease if bitten by an infected tick.

Interestingly, the species was only identified as the vector of Lyme borreliosis spirochaetes in the mid 1980's, prior to which it was only regarded as a carrier of pathogens to farm animals and of the tick-borne encephalitis virus to humans. The situation now is very different, but that's not a subject to be covered here.

Although I've encountered Ixodes ricinus a few times in the garden or when I've been out in grassland areas, the majority of the individuals that I've photographed were found in woodland, both broadleaved and coniferous, but surprisingly I don't have any record of seeing them in the New Forest. Although some of these sightings have been at odd times during the year including January and February, most have been towards the end of April and through May. This is the best time of year, or the worst depending on your viewpoint, to find ticks as this is when they're usually at their most active.

You could come across a mature adult or a host-seeking (questing) nymph at this time, or possibly even one of the six-legged larval nymphs if you've got a keen eye to spot one as they're tiny, although they typically appear a bit later. These are the three active life forms of the species and at each stage they have to take a bloodmeal in order to survive and develop to the next stage or, in the case of adult females, to gain the nutrition needed to be able to produce and lay eggs.

Ixodes ricinus - nymph (ground level on deadwood)

Ixodes ricinus - tiny six-legged larval nymph

Despite the general notion that ticks are blood-sucking parasites that have nothing better to do, it's interesting to note that research has shown that the combined feeding phase of each stage actually amounts to no more than 2-3 weeks, which is

a very small percentage of their complete lifecycle that is usually in the region of 3-4 years but, subject to weather conditions and other factors, could be as much as 5-6 years.

During the free-living (non-parasitic off-host stage) when they're not actually taking blood, they would either be hidden away in the process of digesting the blood and/or moulting or laying eggs, or in a dormant or overwintering diapause phase when development is put on hold, or out in the open questing when they will ascend low-growing vegetation and wait until a suitable host brushes past.

The typical lifecycle of Ixodes ricinus starts with the tiny, six-legged larvae, also known as larval nymphs, or sometimes referred to as seed ticks, which are little more than 1mm in size, that once hatched will wait until their cuticle has hardened before leaving the general vicinity of the nest site and then climb a grass stem or other low vantage point where they will

wait for an appropriate host. At this early stage of their life they will be seeking a suitably sized host species, ideally a small rodent such as a shrew or wood mouse or, subject to the environment, a small mammal. Once they're attached, they will proceed to take blood from the host for around 3-5 days before dropping off and finding shelter in the grass or leaf-litter where they will moult to the nymph stage at which time they will have grown their final pair of legs.

The process will then pretty much repeat except that the second stage nymphs have now grown to around 2-2.5mm in size and will be seeking a larger host like a rabbit or ground-nesting bird. Once again, they will stay attached to the host until they've taken a sufficient infill, then drop off and find a suitable place where they can lay low for a few days to digest the blood and moult to the adult stage.

It's during this period of activity that you need to be vigilant if you're walking through long grass or kneeling down amongst low-level vegetation as you could well find that one has attached itself, whether intentionally or accidently, and given their small size it's quite likely that you may not notice at the time. The infection rate from nymphs carrying a disease agent such as Borrelia is much higher than that of the larvae and, in fact, bites from nymphal ticks are responsible for far more cases of Lyme disease than those from the adults.

Ixodes ricinus - adult female (resting)

Ixodes ricinus - nymph (ground level on deadwood)

However, attention is more often to be given to the adults simply because they're more likely to be seen. In their unfed state they're certainly larger than the nymphs, but not by that much as they probably have a body length of around 3.5-4mm. But once they've fed it's a different matter as a fully engorged female is at least twice that size and possibly as large as 10 or 11mm. Prior to feeding they obviously need to find a suitable host and this is when you're more likely to find one in the open positioned close to the tip of vegetation waving their front legs in a pose known as questing. They're now seeking something larger than a rabbit, whether it be sheep on upland pasture, other farm stock or, more likely locally to me, a deer. But the problem is that there are probably more humans and dogs than deer passing by in many areas and at this stage of their lifecycle they're not going to be too picky. Once attached, the female will now release pheromones to attract a male who will then perform his duties before moving on in the look out for other females to fertilise. His job will then be pretty much done, but the females will stay attached to the host for around 1-2 weeks if not detected and physically removed, as they need to be fully engorged in order to lay their eggs.

I still haven't found an engorged female, but I have seen the odd one where the normally dark reddish-brown body is distinctly red and I presume, as they've been questing, that they've only partially taken a blood meal for some reason and are having to find a new host. Although the general shape and colour of Ixodes ricinus is reasonably distinctive, it's worth looking closely at the dark-coloured dorsal plate, which should be clearly punctured, and also the ends of the tarsi that are tapered. The dorsal plate, known as the scutellum, is shortened in the female thereby leaving a large part of the body exposed and capable of expansion. The males on the other hand, which you don't see very often as they don't feed to any significant extent, have an almost entire plate as can be seen in one of the above photos.

Ticks don't possess eyes, so the only way they can seek a new host is to find a suitable vantage point where they can quest, which effectively involves raising their forelegs that include specialised sensory hairs on the ends of the tarsi. The associated organs can register the presence of a potential host through various means including vibrations and in changes of air movement together with temperature increases and odours that are released by wild animals. The only problem is that they can only spend a limited amount of time in the open before they start drying out so if a host isn't forthcoming, they have to move back down to the ground to recuperate before making another attempt.

Locally I'm more likely to find ticks in woodland rather than in grassland or grazing land, but these days I very rarely see deer or indeed much wildlife at all, so I suspect that many ticks never actually complete the full lifecycle.

Ixodes ricinus - winter active adult female

An active winter adult female found in the garden (Feb.21)

and another on the rim of the garden waste bin (Jan.23)

Ixodes hexagonus (hedgehog tick) is another possible species and, although I've yet to see one, is said to be the most common tick found on cats. They have a similar life cycle and grow to much the same size as Ixodes ricinus. They have a much paler body with pale yellow legs that have a stepped rather than tapered tarsi.

Created July 25 | updated Aug.25 (v.2)