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I used to hear this all the time when I was growing up. Just ignore bees, don't swat at or try to kill them, because if they die, they'll send a "signal" to the hive that will attract dozens more. After forgetting about it for many years, I recently heard the same claim from adults.

I've killed and seen killed several bees and haven't been subsequently visited or attacked by swarms the size of a grand piano, but maybe they were just very far away from their hive.

There's all sorts of anecdotal/non-credible mentions of this claim, but I've never seen anything convincing. For example, from an exterminator's site:

Do not swat at bees. Swatting bees causes the release of an alarm signal and only increases the intensity of an attack by stimulating other bees to attack

Or from a September 1988 issue of Field and Stream:

Don't kill bees. Injured or dying bees are thought to emit a cry of distress, which other bees respond to quickly. The alarm signal sends squadrons of armed investigators to the scene. These rescuers often attack anything that moves or that has body temperature.

Final example from this Associated Content article, which references a semi-trustworthy government source but it is not clear where this specific claim was derived from:

To avoid getting attacked by bees, one should never swat or threaten a bee. The reason for some swarm of bee attacks are due to the release of a pheromone a threatened bee will emit. This pheromone sends a distress signal to all other bees in the area, and will attract the whole swarm to come in and defend them.

It mentions a pheromone being responsible, but the government source, quoting another primary source, only seems to talk about this in the context of colony defense, and if I'm reading it correctly, releasing the pheromone is only really effective in proximity to the hive and is also one of the first things a defender does (long before one would have a chance to swat).

Is there any truth to the claim of dead/dying bees sending off an "alarm signal"? Is it backed by research, or is it just an old wives' tail?

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Why would you want to kill a bee anyway? –  UpTheCreek Jul 16 '11 at 6:03
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You can actually demonstrate for yourself pretty safely, humanely, and easily. Find an ant nest (ants are in the same order/suborder as wasps and bees: Hymenoptera/Apocrita) and molest a single ant with a piece of grass or something until it’s quite upset. You’ll soon notice the surrounding ants become agitated and combative. Just keep an eye on your feet and be ready to move or you might find the experiment is not as safe as I suggest. –  Ashley Jul 16 '11 at 6:34
    
I know its only anecdotal, but I've found the best way to get rid of wasps/bees is to spray them with a water mist. Instead of getting angry they tend to run off and hide under the nearest leaf as they think its raining! –  Nick Jan 18 '13 at 11:07

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up vote 35 down vote accepted

Here's a primary source, a research done on Honey Bees:

The bee's response to the first (alerting) stimulus strengthens her guarding stance; for instance the abdomen is raised, possibly with the sting protruded, and the antennae are waved. In addition, the bee may recruit other bees to guard activity, by entering the colony with her sting chamber open and the sting prodtruded, thus releasing alarm pheromone.

Also, From the Science Daily:

The stinger's injection of apitoxin into the victim is accompanied by the release of alarm pheromones, a process which is accelerated if the bee is fatally injured.

Release of alarm pheromones near a hive or swarm may attract other bees to the location, where they will likewise exhibit defensive behaviors until there is no longer a threat (typically because the victim has either fled or been killed).

These pheromones do not dissipate nor wash off quickly, and if their target enters water, bees will resume their attack as soon as the target leaves

A biology site here tells us there are different types of pheromone released, and the specific one released, is the attack pheromone:

Two main alarm pheromones have been identified in honeybee workers. One is released by the Koschevnikov gland, near the sting shaft, and consists of more than 40 chemical compounds, including isopentyl acetate (IPA), butyl acetate, 1-hexanol, n-butanol, 1-octanol, hexyl acetate, octyl acetate, n-pentyl acetate and 2-nonanol. These chemical compounds have low molecular weights, are highly volatile, and appear to be the least specific of all pheromones. Alarm pheromones are released when a bee stings another animal, and attract other bees to the location and causes the other bees to behave defensively, i.e. sting or charge

So, it is released, but how quickly does it take effect? I looked at a beekeeper's site, because they have the most experience as to the speed with which bees attack after pheromone is released. Let's look at a beekeeping site:

Immediately and steadily back away from the hives, without swatting at the bee, screaming, convulsing, or otherwise freaking out. When you are away from the hives, kill the bee by slapping it soundly. Kill the bee before it escapes from your hair or clothing, as it will likely sting you when it is free. Discard the dead bee outside the apiary and apply smoke liberally to the area on your body where the bee was killed. Smoking the area will mask the alarm pheromone secreted when the bee was crushed.

The pheromone is produced, but it doesn't reach the hive immediately. It will eventually be detected if you are near enough, but it does take some time. If you are far away from the hive, the bees might not smell it either, as the pheromone will dissipate.

That may be the reason why you could kill a bee with impunity. Note also how the beekeeper instructs to back away from the hives, then kill the bee, and then smoke the area. It's safe to kill the bee in two situations:

  • You're far away.
  • You smoke the bee after you kill it.

    The pheromone takes approximately a few minutes to be detected if you are near enough. You are safe for a few minutes. This can be seen here:

    If a bee stings you, don't panic and immediately run, and especially don't make a lot of jerky, sudden movements. This just increases your chances of being stung again. Instead, calmly back away a few feet from the hive and use the edge of your fingernail, the hive tool, or a knife, to scrape the sting sac out from the side. Never grab the stinger and pull it out -- this only injects more venom. After the sting sac is removed and discarded away from your body and the hives, smoke the area of the sting to mask the odor of the alarm pheromone.

    You actually have time to remove the sting sac and smoke the area, and this is being done by bee-keepers all the time.

    So, pheromone is produced, it's not a house-wives' tale, and it does ignite the hive to attack, but you could mask it, or if you are far away, it won't be detected.

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    I listed those sources because they are not primary sources as far as I can tell, and don't cite primary sources (or when they do, seem to extrapolate more than they should from the primaries). The sum total of all of this only tells me that an arbitrarily-sized subset of beekeepers agree; while it's better than nothing, it's not the most convincing of evidence. –  Aaronaught Jul 15 '11 at 1:17
        
    The first primary source you're now citing is the same one I referenced in the question, which states that a pheromone is released, but also states that this is done (a) when guarding the hive and (b) inside the colony. Second source is not primary but does provide references, so it does lend some credence to the theory; what's still lacking is some evidence that (1) a dead/crushed bee releases this pheromone in significant quantities and/or (2) it's detectable by other bees at any significant distance from the hive (i.e. more than a few feet away). Thoughts? –  Aaronaught Jul 15 '11 at 12:49
        
    @Aaronaught, your evidence hurdle for (2) seems too strong. Even if the detection distance is only a few feet, you may be close enough to the hive anyway, or else there may still be other bees within that range. –  Oddthinking Jul 18 '11 at 2:53
        
    How sensitive to bee pheromones are bees? Is the threat response linked to the detection of pheromones regardless of their strength? Do multiple stings simply broaden the trail of pheromones - in effect recruiting more bees - or does it also intensify the attack? Pheromones won't travel upwind, Brownian motion is slow and easily overcome by a slight breeze - moving downwind of the hive would seem an obvious strategy. –  Duckisaduckisaduck May 7 at 14:09

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