Car recalls and Mazda's mystery spider

From a spider’s perspective, it probably seemed like a good place to spend the winter: a hard, rubber tube half-an-inch wide. Dark. Web-friendly.

Who knew that it would spark a 65,000-car recall – and a budding auto-arachnid mystery?

Entomologists, not to mention Mazda, are scratching their heads, trying to figure out how at least 20 yellow sac spiders found their way into the vent pipes of Mazda6 cars, but only in 2009 and 2010 models.

Did they just prefer the new cars assembled in Flat Rock, Mich.? Exactly how did they get in? And when?

The vent pipe of a Mazda6 isn’t exactly accessible. And the spiders, which only live a year, don’t cotton to the cold of a Michigan winter. At least two theories are competing for attention.

According to Mazda, the yellow sac spiders, less than half an inch long, got in after the cars were assembled. That’s because some of their webs were found recently in 2009 models. Since the vent pipe sucks air out of the fuel tank and then pushes it back in, there’s no way that a yellow sac could last in there last two years, says Jeremy Barnes, a spokesperson for Mazda.

While its unlikely their webs could last that long either, the company is recalling 65,000 Mazda6s because vent pipes clogged with webs don’t release enough air back into the fuel tank, and may cause it to crack, Mr. Barnes says.

Some entomologists speculate that the spiders got into the pipes before the cars were assembled because the infestations are so car-specific. If it was happening in drivers’ garages, infestations would be widespread, since so many cars have a pipe similar to the Mazda6’s and yellow sac spiders are common throughout the United States and the world, says Susan Jones, who is an entomologist at Ohio State University in Columbus.

The placement of the vent pipe also suggests that the spiders got in before the cars were assembled. “There’s nothing that would make a yellow sac spider be attracted to gasoline,” she adds.

They do like to spend the winter in “an undisturbed place, an out of the way place,” professor Jones says, like under a rock or board, or perhaps in a vent pipe.

One important clue is that there are different kinds of yellow sacs, which spin different kinds of webs and behave in different ways. For instance, Jones says that the yellow sac spider in Ohio spins a little refuge up on the ceiling, and would probably not choose to spin its web in a vent line.

That means, the spiders wouldn’t have crawled in anywhere near Ohio State University.

If all the spiders that are discovered in the Mazdas are the same species, it means that there’s a good chance they all crawled in the vent pipes in the same location.

Mazda continues to look for the source, Barnes says. No word yet on whether they know whether the webs are all spun the same way.