Sometimes, life is better than I can imagine.  Insecty news has been dominated by this story the last couple of days:

Mazda recalls 65,000 cars for spider problem
A spokesman from Mazda said that yellow sac spiders (Cheiracanthium)  built small webs in the crucial vent lines. If those vent lines were to get fully blocked by webbing, the car’s fuel tank could conceivably build up enough pressure to crack and leak fuel….
Mazda identified the culprit as the yellow sac spider, or
Cheiracanthium inclusum. The pale, mildly venomous creatures lay their eggs in silk-wrapped bunches — usually in vegetation.   But why they’re choosing Mazdas instead of, say, Porsche Spyders, is a mystery. As is the fact that only the 4-cylinder Mazda6 cars are playing host.

There are a lot of really interesting clues in these stories about just WHY a specific type of spider would take up residence in a fuel vent line. I found the official recall notice, but it was rather spare of specifics.   But don’t despair! Click and Clack at Car Talk have the scoop:

Beverly Braga, Product Communications Specialist for Mazda, assured me that yes, there have been 26 confirmed cases in which the webs of yellow sac spider have caused problems by blocking the evaporative canister vent line of certain 2.5-liter four cylinder vehicles.  Allen Dean, a research assistant at the Texas A&M University Department of Entomology, says it’s curious that this particular spider would be the culprit because they aren’t known for their large webs, unlike orb or tunnel web species. Ms. Braga confirms that no one seems to know why yellow sac spiders are attracted to the car or how they find their way into the fuel system. No fires, accidents, or injuries have been connected to this problem, but company engineers thought 20+ cases was too many to be a coincidence so Mazda is taking a proactive approach.

To say a bit more about the spiders involved–Sac spiders normally occur in your garden, and are relatively harmless, although they do have an irritating bite.  The term “sac spider” does NOT mean they spin webs in scrotums, which was the alarmed conclusion of one person I talked to.

Although, spider webbing probably would be pretty supportive and wick well….UnderArmor would have nothing on web underwear!

Wait. I digress.

Sac Spiders spin tubular webs, an example of which you can see in this image.  It’s kind of a sleeping bag affair, in which the spiders hide in the daytime.  These spiders are photographed on a blade of grass, so that should give you a sense of scale–they are tiny fellows, usually not bigger than 6mm.

The spiders come out and forage at night, so you can kind of see why a vehicle up off the ground would make a nice daytime retreat for an active hunting spider.

I like to imagine them snug in the fuel vent line, saying in a tiny, tiny voice: “Zoom Zoom this, sucka!”

Posted by Gwen Pearson

Entomologist. Educator. Writer. NERD.


  1. That was fun! I’m doing spider surveys in the Austin, Texas, area and find that most Yellow Sac Spiders (Cheiracanthium inclusum) live in triangular-shaped sacs. Even so, those I’ve kept for observation have made sacs in a variety of shapes. I suspect that this spider is found making homes in the tubes of cars for the following reasons:

    (1) The spider is very common, making them statistically more likely to be the culprit.

    (2) The spider is fast and covers a lot of territory, including vertical territory, while wandering for food.

    (3) The spider makes a sac retreat, so that a nest by this spider would actually clog the tube.

  2. Hearing this on NPR this morning brought much delight. One more to add to Joe’s v. solid list: (4) This particular species has a strong genetic predisposition to gambling addiction, so is always broke and anyone, like an unnamed Toyota representative, could easily hire them to wreak havoc.

  3. Aw, man! Someone pointed out a great pun I missed:

    Ziggy Stardust and the Spiders from Cars

  4. The specificity to the 4-cylinder model isn’t much of a mystery; in fact, it makes a great deal of sense. Most likely a run of this particular model was stored somewhere prior to distribution where a large number of sac spiders were present. Some of the spiders holed up in a few cars while the cars were waiting to be shipped. This seems to be one of the more plausible explanations to me.

    With a small amount of effort I can usually locate one or two in my house, so they’re hardly unusual. I’d spend some time looking in warehouses instead of recalling cars if I wanted to head off the problem at the pass. Exclusion, folks, exclusion! It’s the best IPM out there.

  5. Come to think of it . . . they could have holed up in the parts before the parts were even installed in the car. That seems even more plausible – the parts could be stored anywhere prior to installation, and may even escape JIT inventory policies, inviting more spiders to snuggle up and get comfy until production caught up with the supply of parts.

  6. I thought that too, Chris, except that they showed up in several different model years from different locations. Looks like it’s just a spider magnet :)

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