English wildlife has very few dangers. Adders – our only venomous snake – are scarce, shy and non-deadly to humans. European hornets (Vespa crabro) look and sound intimidating, but are rarely aggressive. Even the plentiful moon jellyfish (Aurelia aurita) that sometimes swarm beaches and harbours cannot sting.
Yet I am wary of one creature, especially in summer. Usually less than 1cm long, it is typically found in areas of rough grazing, woodland or moorland where there are rabbits and wild deer.
Exmoor provides a perfect habitat, and it is especially abundant here. In recent days, I have found many crawling through my dog’s fur, or hanging like dark, berried drops around her nose and eyes. These are ticks: blood-sucking arachnids that feed on mammals, including people.
I have never known ticks to be so numerous as they have been in the last few weeks. It’s not just my perception; scientists at Bristol University are getting reports of a sudden rise in numbers. They think that this year’s cool, wet spring delayed tick emergence, and then the warm May caused a sudden flush of vegetation, providing ideal conditions for their survival.
After a walk in Horner Woods, I find seven on my dog’s head, picked up while she was nosing herbage along the side of the path. These are castor bean ticks (Ixodes ricinus), bay-coloured with chestnut-brown, seed-shaped bodies and black legs. Hedgehog ticks (Ixodes hexagonus), the species found most often on cats, seem to be less common. Measuring no more than 4mm when unfed, the fully engorged hexagonus females can bloat into greyish-white blood-swollen bladders of up to 1.3cm long. Ticks find hosts by climbing plant stems and waiting, forelegs outstretched, sensing heat and movement. When an animal brushes past, the tick hooks on, seeking a spot to bury its hypostome, the barbed tube that anchors it in place and through which it sucks.
As with other parasitic lifeforms, feeding can transmit bacteria into the host’s circulation. Some ticks carry Borrelia burgdorferi bacteria, which cause Lyme disease, a debilitating illness requiring treatment with antibiotics. And it’s not only a countryside issue – the castor bean tick can be found in city parks across the UK.
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