To defeat ticks, we must first defeat the lizards

The Western fence lizard was once believed to be our best defense against lyme disease. That's because ticks carry lyme disease, but lizards carry a lot of ticks. In fact, ticks are so enamored of lizard blood that they basically act as a buffer zone between humans and lyme disease - as long as the Western fence lizard is around, ticks will always prefer its cold blood to ours. So what happens if the lizards die out or go away? Are we facing a lyme disease catastrophe? Some UC Berkeley researchers decided to find out.

Led by biologist Andrea Swei, the group rounded up lizards in 14 different regions of Marin County, California. They wanted to see where the ticks would wind up if they didn't have lizard snacks. Would they turn to other animals, or people? What they discovered surprised them.

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According to a release about the group's findings, published yesterday in the Proceedings of the Royal Society B:

From March to April 2008, before tick season went into full swing, the researchers captured and removed 447 lizards from six plots – three at each site – and left the remaining plots unaltered as controls. The lizards that had been captured were marked [with liquid paper] before being relocated so the researchers could determine whether any wandered back into their old haunts.

After the lizards were removed, the researchers spent the following month trapping other mammals known to harbor ticks – particularly woodrats (Neotoma fuscipes) and deer mice (Peromyscus maniculatus) – to determine whether they bore an uptick in ticks as a result of the lizards' absence. The researchers also checked for differences between control and experimental plots in the abundance of host-seeking ticks by systematically dragging a large white flannel cloth over the ground.

The researchers found that in plots where the lizards had been removed, ticks turned to the female woodrat as their next favorite host. On average, each female woodrat got an extra five ticks for company when the lizards disappeared.

However, the researchers found that 95 percent of the ticks that no longer had lizard blood to feast on failed to latch on to another host.

"One of the goals of our study is to tease apart the role these lizards play in Lyme disease ecology," said Swei, who is now a post-doctoral associate at the Cary Institute of Ecosystem Studies in New York. "It was assumed that these lizards played an important role in reducing Lyme disease risk. Our study shows that it's more complicated than that."

So the takeaway message here is that the lizards were never really on our side. They weren't trying to protect us from ticks at all. And ticks are a lot more faithful to lizards than we ever knew.

You can read the full scientific article in the Proceedings of the Royal Society B.

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