To monitor species numbers and survivorship year after year, the pair had to come up with a reliable way of marking tarantulas. That's a significant problem in a species that molts on an annual basis, shedding any markers. Some kind of internal tag was necessary, but such a procedure had never been attempted. The solution was to surgically implant rice-grain-size radio transponders that passively transmit a serial number when scanned with a portable device.
"I'd been bumbling around with various schemes of leg painting and this just seemed like such an obvious use for [radio] transponders," said Reichling. "I got the idea from my zoo job, tagging the reptiles and thinking that the spiders I work with are larger than some of the animals we were marking."
Tabaka has perfected a technique to implant the tags into tarantula abdomens. The procedure can have complications, however. Spider blood doesn't clot for a start, so botched surgery can be fatal. "Imagine trying to implant a marble in a balloon filled with water, without deflating it!" said Reichling
In addition, Belizean tarantulas are often covered with stinging spines, which can be breathed in, or damage human skin and eyes, so protective clothing must be worn. Despite the complications, the surgeries typically go smoothly and most tarantulas emerge unscathed.
With the aid of a portable scanner the scientists can scan the burrows each year to see if tarantulas are still in residence. If they find burrows that don't turn up a signal at any of the sites, Reichling says they'll catch and tag new residents.
Studying the whole range of spiders in a habitat has previously been used to measure pristine or altered environments, said Paul Hillyard, arachnologist at The Natural History Museum in London, "but surgically tagging invertebrates is certainly novel." However, the surgical procedure is very invasive, and potentially dangerous to the tarantula, he cautioned.
Though the study has yielded few results as yet, some of the habitat has already been totally destroyed in two of the three study sites, "to make way for a soccer field and a Maya ruin visitor center," said Reichling. "I almost lost heart but decided to go ahead anyway, and document this tremendous disturbance."
The project is detailed in a recent edition of the journal, Biologist.
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