Friday Weird Science: Does your menstrual blood attract BEARS?!

Feb 03 2012 Published by under Friday Weird Science

While Sci was listening eagerly to Kate Clancy's appearance on Skeptically Speaking last Sunday (you'll be able to download the episode soon), I was flabbergasted to find out that there is a rumor out there that, if you go out hiking on your might attract BEARS.

(I totally forgot about this until someone on Twitter pointed it out. Awesome)


Not only that, the rumor was apparently widespread enough that someone actually did a study to find out if it was true.

Which is good, I'd hate to fear for my life while hiking because I'm shedding my uterine lining. I'd like the think bears are more sensible than that.

But I'll admit, a part of me was a little worried. After all, I have been camping, and had our campsite raided by bears, because someone left their toothpaste out of the bear box. Apparently bears in Yosemite National Park love them some minty freshness. And if toothpaste is on the menu, why not tampons? I mean, bears will eat most anything, right? Luckily, science is here for us, and science wants us to know, it's ok to menstruate around bears. Black bears, anyway.

Rogers et al. "Reactions of black bears to human menstrual odors" The Journal of Wildlife Management, 1991.

So apparently this whole fear of bears loving the scent of your menstruating ladybits comes from an attack on two female hikers in 1967 by grizzly bears (today I learned the scientific name for Grizzly is Ursus arctos horribilis, how apt) in Glacier National Park. The women were both apparently menstruating (no one has the original source for that information, though, and neither girl lived to tell the tale). This made people panic, and people actually issued warnings to not hike in bear country while menstruating, even though both attacks took place where there was lots of trash around to attract bears for tourists, and several reviews of major deadly bear attacks have stated there's no evidence for menstruation being involved.

But apparently it depends on the bear. The paper states that polar bears will willingly nosh on tampons soaked in menstrual blood and ignore tampons with normal blood. I'd like to see that one replicated, since there's no record of polar bear attacks being associated with menstruation either.

Anyway, this paper concerns black bears. These are by far the most commonly sighted by hikers, occurring throughout North America. I've seen a few of these myself (free tip, hiking friends, do not pose your children next to the adorable bear cubs for a photo. I have seen this happen). The authors took 15 used tampons (no record of how old they were or if they kept them fresh, or how long they were in), and presented them to a group of 5 black bears feeding on a trash heap. Via fishing pole.

They attempted to get the tampons (which were in a bunch) as close to the bears as possible, and then observed whether the bears picked tampons or trash. They considered the tampons "paid attention to" if the bears 1) ate them, 2) sniffed them with interest, or 3) rolled on them. They did this again with another group of used tampons, these first frozen and then thawed (mmm).

For their second experiment, they took 6 used tampons from 6 women. They went to a spot where people commonly attracted black bears with corn (and hand fed them, no less), and manually presented the tampons to the bears.

Then, they laid out 4 used tampons, some non-used tampons, some tampons with human blood on them (not menstrual), and some tampons with beef on them, and put it by a well used bear trail. They had 12 bears stop on by, and watched what they did.

Then they did something REALLY wild. They had 7 menstruating women HANG OUT with bears. The women hung out near the bears, even hand fed them (the bears were apparently well used to this). And they watched to see how often the bears sniffed at the women's ladybits. I'm not kidding. They first had seven ladies hang out with bears, and then they had one hand feed bears on and off her period for two months (wearing pads, not tampons). Would you hang with a bear for science?

For all of tests, with menstruating women or used bears don't care. Regardless of mating season, the sex or heat state of the bear, the freshness of the tampons, or basically anything else. Black bears just don't care about your period problems, apparently. The bears tested with tampons soaked with beef fat found that pretty awesome, but ignored all other tampons.

The authors suggest that black bears may care less about menstrual blood than polar bears because black bears are more omnivorous. Given that polar bears eat exclusively meat, they may be less picky, but the authors also note that several of the bears tested had recently eaten young deer. I do have to wonder, if polar bears were tested again, if they might be just after the blood, regardless of where it came from. It could also be that none of the black bears were all that hungry, food was pretty abundant.

Obviously there are plenty of issues with this paper. There was only one comparison to blank tampons OR non-menstrual blood. There was only one comparison for a woman not on her period. There were no comparisons with men (I mean, at some times, wouldn't taint odor be plenty bad too??). The bears weren't hungry, and usually had other bear things to do. What's clear is that menstrual blood is not exactly a preferential food for black bears. So unless you're out and around some seriously hungry bears, the woods are relatively safe.

Rogers, L., Wilker, G., & Scott, S. (1991). Reactions of Black Bears to Human Menstrual Odors The Journal of Wildlife Management, 55 (4) DOI: 10.2307/3809511

28 responses so far

  • S Mukherjee says:

    Thanks -- this was a lot of fun to read. I assume those women who use menstrual cups are safe anyway, since they wouldn't be discarding used tampons?

    I am always suspicious when people say 'Women who are menstruating shouldn't do X activity.' It's as if women, who are regarded as 'not-people' and troublesome at best, become extra troublesome when they are in that time of the month. Rubbish.

  • N Akpan says:

    "Well that’s just great. You hear that Ed? Bears! Now you’re putting the whole station in jeopardy!"... glad we can put that myth to rest.

  • Pascale says:

    What I really want to know is if menstruating women are more likely to get attacked by sharks with their keen sense of blood detection, etc.
    Hello, Science?

    • scicurious says:

      You know, I wondered this too! I looked it up, and no one has done a study. Will no one dangle bloody tampons in the water for science?! I'm thinking a pretty easy study design, blank tampons vs bloody tampons vs tampons with menstrual blood. Now all I need is a fishing pole and some sharks...

  • Sherlock says:

    So what do you think are the odds that this theory was first put forth by a man who wanted some alone time. "I'm sorry honey I don't think it's a good idea for you to go hiking with me today, you know bears are attracted to women having their period. "

    So who wants to test the same thing with sharks?

  • Ken says:

    Great read, thanks for that coverage. I have wondered about it ever since I read about the grizzly attacks in Glacier National Park. I think the book was Jack Olsen's 'Night of the Grizzlies'. A little dramatized, but also well-researched, and definitely repeated the period hypothesis. But those were some weird grizzlies, used to foraging in dumps. Needless to say, tampons can be found in dumps. Someone needs to redo the study with grizzlies (except for the part with the live women!).

  • KateClancy says:

    This was AWESOME Sci. Thanks for covering this, and as always doing it so well!

    And I am not signing up for the shark study.

  • Felix says:

    I wonder if bears Menstruate. I mean, if they do, it's quite plausible for them to take it as a sign that you shouldn't mate with that female (which raises the possibility that on heat women are more at risk). Furthermore, they may have the same ick factor we do :P.

    I tried to google this, but unfortunately all the results are for bears and human women.

    • Ken says:

      I think most bears come into heat once a year, or maybe every other year after their last kids are on their own. So, no need.

    • Amy says:

      Menstruation only occurs in primates, some kinds of shrews and hedgehogs, and a few kinds of bats. For some of these, though, the blood loss is so little that it is barely noticeable. "True" menstruation as we would recognize it really only occurs in primates, mostly the great apes and humans.

      Some other kinds of mammals undergo a "covert" type of menstruation, in which the uterine lining is shed and reabsorbed internally without ever leaving the body. These are usually the ones that have a regular "heat" cycle - if there is no fertilization, then the covert menstruation occurs.

      It has to do with decidualization - the thickening of the lining of the uterus. Most mammals undergo triggered decidualization once a fertilized embryo is implanted. A few mammals undergo spontaneous decidualization though, and build up a thickened uterine wall even in the absence of an embryo.

      Why? In some species, the embryo implants very deeply, actually attaching to the maternal blood vessels. In these species, it is advantageous for the mother to build up the uterine wall in advance, to protect herself from the fetus. The mother needs to survive the pregnancy in order to reproduce again - but the fetus is busy trying to wrest as many resources from the mother as possible. Its a kind of tough relationship. In all cases where the embryo implants very deeply, spontaneous decidualization, and thus, menstruation occur.

      (tl;dr: no, bears do not menstruate!)

  • Ericka says:

    Loved this one. I had a history teacher once who told the class that he went on vacation to a place with komodo dragons, and they "went crazy" over the smell of some of his traveling companions, who were on the rag. How he knew they were on the rag and why he attributed the animals' behavior to this is beyond me.

    • stripey_cat says:

      As a kid, I was solemnly told to avoid male horses (especially stallions, but also geldings prone to stallion-like behaviour) when ovulating, after an incident where an instructor was injured by a gelding trying to mount her. Of course, many years after the event, I realised that it was 99% likely that the horse was in the mood to mount anything that moved, and her hormonal status was totally irrelevant as well as being pretty different from a mare in heat.

      In other words, conformation bias.

      (It is also possible that the Komodo dragon was genuinely smelling blood and reacting as a predator that keeps an eye on injured victims: in that case, I suspect the woman would have said she was on her period, especially if the guides or safety information warned about blood as a possible problem.)

  • I always think of the film "Pitch Black", where the young woman (who spent about 90% of the plot disguised as a young man, with short hair) is blamed for the alien monsters tracking them down, because they sense she's menstruating somehow.

  • [...] last week's post on whether the bears can smell the menstruation (hehe, I can't get over that quote), I was inundated with questions and tips for papers. People [...]

  • Knutz says:

    We had a female dog at my job and she would only sniff certain women's crotches and only at certain times and never very old women I wonder what was going on there . Us guys would look at each other and wink but we never got exact proof these women eh you know

  • alan says:

    I think that we are looking at this problem the wrong way. It is not a question of whether a menstruating woman is safe near a bear. I have been married a long time and have never felt safe near a menstruating woman. Perhaps bears have more sense than we give them credit for. Every bear I have ever seen had the sense to run away from humans.

    • scicurious says:

      And if I was married to someone who liked to joke about how they didn't feel safe while I was menstruating, I'd make it my mission to make him miserable regardless of the time of month.

      This is a sexist comment. I understand you mean to be funny, but stuff like this demeans women, both women who can menstruate without anyone being able to tell the difference, and women who suffer greatly during their periods. I'm not a fan.

    • Gerty-Z says:

      wow. I wonder if bears avoid total douchebags. Because then any woman with you would be safe.

  • TK says:

    This myth also got name-checked on "Parks and Recreation" a while back, in the episode where Amy Poehler's character gathers all of the former department heads for the Pawnee catalog photo.

  • [...] “The authors took 15 used tampons (no record of how old they were or if they kept them fresh, or how long they were in), and presented them to a group of 5 black bears feeding on a trash heap. Via fishing pole. They attempted to get the tampons (which were in a bunch) as close to the bears as possible, and then observed whether the bears picked tampons or trash. They considered the tampons “paid attention to” if the bears 1) ate them, 2) sniffed them with interest, or 3) rolled on them. They did this again with another group of used tampons, these first frozen and then thawed.” ( [...]

  • [...] talk about bears again, my friends. We have already learned that, contrary to popular belief, they cannot smell the menstruation (or rather, they probably can, but don't [...]

  • John says:

    The women in Glacier were attacked by Grizzly Bears, the study you're quoting was done on Black Bears. Since Grizzly Bears are Man/Women eaters, I suggest that you ladies still take caution when Grizzlies are around, i.e. in Yellow Stone, Glacier, or anywhere in Alaska.

  • Kaci says:

    Thank you cause in the summer I'm going camping and I was scared that a bear is going to attack me now I'm not as scared.

  • […] Store personal items (such as deodorants, toothpaste, soap and lotions) with food and garbage when not in use. – Any odorous product may attract bears. […]

  • […] that bears are attracted to menstruating women. At least for black bears, this myth is just that. Three experiments were conducted in the early 1990s that attempted to measure a black bear’s attraction to menstrual blood. The first experiment […]

  • Megan says:

    Hah! I thought Alan's comment was funny.

Leave a Reply