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Wild Things

The weird and wonderful in the natural world
Sarah Zielinski
Wild Things

Yet another reason to hate ticks

The American dog tick, Dermacentor variabilis, is one of several tick species that has a bite that can cause paralysis.

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Is there anything redeeming about a tick? These small arachnids — of which there are 850 members in three families in the order Parasitiformes — latch onto the skin of a pet, human or other animal and suck their blood. This classifies them as ectoparasites — a parasite that lives on the outside of a host.

We find ticks to be scary not simply due to their blood-sucking ways but because some ticks transmit diseases. People in the United States, for example, risk contracting illnesses such as Lyme disease, Colorado tick fever and the recently discovered Heartland disease. Outside the United States, there are plenty of other tickborne diseases. And pets and other domesticated animals are also at risk.

But it seems we may be missing another reason to fear ticks. In addition to being blood-sucking disease carriers, they’re also venomous, Alejandro Cabezas-Cruz of the University of Lille Nord de France and James J. Valdés of the Biology Centre of the Academy of the Czech Republic in České Budějovice argue July 1 in Frontiers in Zoology.

“Ticks are rarely considered as venomous animals,” Cabezas-Cruz and Valdés note. (A venomous animal is one that is capable of administering a poison through a bite or sting.) But there are plenty of reasons to classify ticks this way. To begin with, tick saliva is known to cause paralysis. Such an outcome from a tick bite is thankfully rare, and that might be one reason why ticks haven’t generally been considered venomous. But about 8 percent of tick species can cause paralysis with a bite.

Paralysis is just the beginning, though. Tick bites have been known to cause other symptoms, including pain, fever, inflammation, itching and blisters.

Where a tick bites and how many ticks bite a person matter, the researchers note. For example, a 3-year-old boy from India suffered from left-sided facial palsy because the child had a tick infestation in his left ear and had been bitten near a facial nerve.

In classifying tick saliva as venom, Cabezas-Cruz and Valdés observed that the saliva not only had lethal toxins but also proteins similar to those found in the saliva of other venomous animals, including bees, spiders, scorpions and snakes. And, the scientists say, tick saliva is far more similar to that of venomous animals than to that of humans and other non-venomous creatures.

These observations might provide some insight into the evolution of ticks, spiders and scorpions: The similarity of saliva proteins between these three groups of arachnids suggests a common origin of their venom systems, the researchers note.

This research, however, probably doesn’t mean much for someone who has been bitten by a tick; the dangers of tick bites have been known for a long time. Classifying ticks as venomous is more of a reminder that people need to take measures to protect themselves from tick bites, especially in warm months, such as now, when we’re more likely to encounter the blood-sucking, disease-carrying, venomous beasties. 

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