Mythbusting: gas-sniffing spiders are NOT invading our cars

7 April 2014 by Christopher Buddle, posted in Miscellaneous, Spiders

Today the BBC reported on the giant recall from Mazda because of a "spider invasion" that is requiring a software update on over 40,000 cars. This is not a new story, but it's taking off today. I was particularly intrigued by the following statement on that website: "...The yellow sac spider is attracted to the smell of petrol".

Cheiracanthum inclusum - photo (c) J. Lapp, reproduced here with permission

Gas-sniffer? Cheiracanthum inclusum - photo (c) J. Lapp, reproduced here with permission

Ok, now I've heard it all. Don't get me wrong - I'm not surprised that spiders are finding their way into various parts of cars: spiders get everywhere!  But can spiders really sniff gasoline?  I did a quick literature search, and although some spiders are attracted to certain 'cuticular hydrocarbons' (i.e., hydrocarbons found within the exoskeleton of arthropods), I have yet to find a scientific paper that suggests they are attracted to gasoline used in our vehicles.  In my professional opinion: Spiders are not gas-sniffers!

Here's what I think is going on: in one car manufacturing plant, there were many sac spiders around, and a few (a lot?) of these arachnids found their way into various parts of some of the cars being put together in that plant.  The documents from Mazda actually support this. There appears to be a single plant (in Michigan) where the most recent events occurred, and to quote those documents: "spiders may weave a web in the evaporative canister vent hose, blocking it and causing the fuel tank to have an excessive amount of negative pressure".

Did you read that...? they "MAY" weave a web in the evaporative canister.  I have not found any documents to suggest they are specifically attracted to that part of the car. Perhaps it is just a nice habitat (?): dark, and maybe the correct shape and size.

Don't get me wrong: I'm not suggesting Mazda was wrong in putting this recall into place. Undoubtedly, it sounds like there's a problem that needs addressing, and that problem may be associated with the webs/silk from sac spiders. However, somewhere along the line, it was suggested that the spiders are actually smelling petrol, and before you know it's a SPIDER INVASION caused by terrifying gas-sniffing arachnids.  It seems that this may have been started by an automotive journalist, reported here in 2011. In that piece, Mitsuhiro Kunisawa reports "this spider's distinguishing characteristic is that it likes the smell of gasoline...".  I will do my best to contact that journalist and ask about the evidence for this: I just don't buy it.

The 'sac spiders' implicated in this story are very, very common, especially in human-buildings. I've written about these before, and it should be no surprise that Cheiracanthum are hanging around a plant that is manufacturing cars. Heck, they hang around our kitchens when we are manufacturing food! They tend to hide around crown moulding, and other nooks and crannies within our houses.  But please, folks, they aren't crawling up tail-pipes, or seeking nooks and crannies of the seat-cushions of your Mazda, waiting to jump out and bite. Please drive with that peace of mind. (Zoom Zoom).

Cheiracanthum inclusum - photo (c) J. Lapp, reproduced here with permission

Cheiracanthum inclusum - photo (c) J. Lapp, reproduced here with permission


15 Responses to “Mythbusting: gas-sniffing spiders are NOT invading our cars”

  1. Juan A. Sanchez JR Reply | Permalink

    Your comments certainly make sense. I couldn't figure out what 'gas loving' insects the spiders would catch in their webs, after all they can't just be high all the time and not eat.

    • Christopher Buddle Reply | Permalink

      Thanks for the comment! There is a LOT of confusion with this entire story - but the one "fact" that's clearly the MOST mixed-up is the claim the spiders are attracted to petrol!

  2. Julie Royalton Reply | Permalink

    Found it amusing that no other car manufacturer had similar claims. As if spiders can only read Mazda!

  3. Kara Manke Reply | Permalink

    I was in the early process of researching my own blog post on why spiders might be attracted to gasoline tanks when I came across your article! I did find one interesting reference stating that certain species of spider are attracted to volatile compounds in plants (Nelson, et al. J Chem Ecol. 2012 Sep;38(9):1081-92). Some of these compounds are large hydrocarbons, potentially similar in "smell" to the volatile compounds in gasoline. However, I did notice that the quotes on "gas-sniffing" spiders all came from the automotive industry - not scientists!

    • Christopher Buddle Reply | Permalink

      Hi Kara - thanks for the comment! That reference is interesting - I wonder if that study involved sac spiders? But yes, overall, any of the arachnologists I talk to tend to find the 'gas-sniffing' as not very plausible!

  4. Emily Reply | Permalink

    Please let us know if you hear back from that "journalist". I am very curious to know why only this model of Mazda cars (many years' worth of models) have this problem if "spiders are drawn to the smell of fuel." Also why this specific spider only. The Mazda rep says it's due to the 2 pipes leading out, implying this splits the fumes, so that there's not enough in 1 pipe to kill the spider. So... all our gas cars are gassing spiders to death all the time? Massive bait-lured genocide? It certainly wouldn't be the 1st unwitting human genocide of fauna.

    The spider called out in the study Kara refers to is the East African jumping spider. The article goes on to state that this spider is unique in having "innate olfactory affinity" for a specific plant species, but that it is known that many insects have a preference for specific blends of "volatile compounds" they use to identify a plant species. Certainly it can be seen as an evolutionary advantage for a spider to be drawn to the smell of a specific plant that its prey is also drawn to. But it's a tremendous leap to "all spiders are uniquely drawn to gasoline."

    Study link:
    http://www.researchgate.net/publication/230722678_Mediation_of_a_plant-spider_association_by_specific_volatile_compounds/file/5046351e1dbd45c16c.pdf

    • Christopher Buddle Reply | Permalink

      Thanks Emily!! I have now found some information on the journalist, and will let you know if I hear back. I very much agree - it's highly unusual to think that spiders would be attracted to gasoline, even if there are some volatiles associated with plants.

  5. James Brown Reply | Permalink

    Up at the farm, we used to use a little bit of gasoline to kill wasps. Never tried it on spiders, but I don't see why the effect would be different

  6. shwn Reply | Permalink

    isnt the point of the recall about the system programming? the recall is not really spider-based. so while it does assert that the fuel tank will attract spiders(or maybe just the prey? i dont eat in my car but i have to keep a raid trap under the seat).theyre just adjusting the cars system to the possible increase in pressure. which will make the spider seem secondary to the sudden engine fire. Either way its the webs that are the problem-unless youre mazda and need something to distract ppl. but can webbing really cause dangerous fuel tank pressures?

    • Christopher Buddle Reply | Permalink

      Thanks for the comment - that's my point, exactly. I'm not questioning the importance of the recall, but rather the assertion that spiders are attracted to the smell of petrol, and they are certainly not 'invading' cars. The point about 'webs' being the causal agent is a 'potential' cause, according to the Mazda documents about the recall.

  7. Dale Reply | Permalink

    Suzuki is now having the same problem:
    "Spiders drawn to gasoline vapors and weaving webs that block a hose to vent those vapors have caused Suzuki Motor of America to recall about 19,000 Kizashi mid-size sedans from model years 2010 to 2013, U.S. regulators said on Wednesday."

  8. David Brooks Reply | Permalink

    Each of these car models, in fact the one in your own garage, is equipped with a fumes trap designed to manage effluent petrol fumes from the petrol tank during times the petrol is evaporating, mostly when the car is parked. The box of activated carbon would eventually become saturated with fumes were it not for it always being regenerated via a small tube connected to the the engine's vacuum present while the car is driven. Presumably, the spider's life cycle includes egg production with provision for protecting those forward to pupation and full maturity.
    If the egg sac is dense enough inside the ambient port (vent) of the box of charcoal, the dense silk could inhibit the purging air flow necessary to sweep away the stored fumes into the running engine, but worse, could simultaneously induce unscheduled suction inside the petrol tank.
    Most petrol tanks' structure design is to hold the weight of the petrol, but not for vacuums acting to collapse the tank. Under suction from the engine there is no internal structure to prevent inward tank surface deflection. Over months of repeated cycling of the tank's walls back and forth between suction, then ambient barometric pressure, every time the car is used, a fatigue crack could be induced in the tank's surface, one with potential to seep liquid petrol.
    This possibility attracts the attention of agencies like NHTSA, while the reason the charcoal is there in the first place to adsorb and to be purged clean is to comply with requirements of agencies like US-EPA.

  9. Bill Crook Reply | Permalink

    I have a 2011 Ford Flex that twice now I have had a very difficult time putting gas into my car in the fall. Once last Oct. 2013 and the culprit was the fuel vent line webbed in the interior. Today ( Sept. 30, 2014 ) I was at the dealer for the same problem but today I asked to see the problem so next time I will know how to fix it myself. The vent hose with protective cap to keep out most big stuff was pulled out of a chassis compartment. Pull off the plastic vented top and sure enough, it was webbed over inside. Must be really small spiders getting inside as the slots are maybe 1/16".

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