1. How does a hive learn that a bee has stung?
Honeybees leave their stingers in the skin of whatever they sting because the stinger has barbs like a fishhook. Because of this, the bee that stings dies [2]. But for the hive, the act of stinging is also a signal. When a bee extends its stinger, organs around it produce alarm pheromone [4]. Bees that smell this pheromone begin to act aggressively [1]. One bee’s action prepares the whole hive for defense.
But what exactly is this smell made of? The answer is not just one substance. It includes at least two different chemicals. We will look at the first one found in the next section.
Safety Note: Stinging behavior is a signal that warns other bees of danger. If you see bees, do not touch them or chase them. Keep your distance to stay safe.
2. Isoamyl acetate: the first alarm chemical identified
The first chemical identified was isoamyl acetate (also called isopentyl acetate). In 1962, Boch, Shearer, and Stone reported it as the active ingredient in the alarm substance from the bee’s sting [3]. Later reports showed it is also part of the venom itself [4].
However, this was not the whole story. In 1982, Pickett, Williams, and Martin found a second component called (Z)-11-eicosen-1-ol coming from the sting. In experiments using moving targets at the hive entrance, this second chemical caused stinging behavior just like isoamyl acetate did. When both chemicals were mixed together, they worked about as well as natural extracts from the sting [5].
The amount is about 5 micrograms per worker bee. Since 1 microgram is one-thousandth of a milligram, 5 micrograms equals 0.005 milligrams. So far, this answers the main question: the alarm smell involves at least two components. But what happened to another substance long thought to be part of the alarm?
3. Is 2-heptanone an alarm scent or an anesthetic?
2-heptanone, which comes from the mandibular glands (jaws), was also once thought to be an alarm substance. As research continued, scientists began to doubt this idea.
A report in 1970 showed that to cause a similar warning reaction at the hive entrance, 2-heptanone needed 20 to 70 times more concentration than isoamyl acetate [6]. In experiments by Vallet and colleagues in 1991, direct alarm effects were not seen on guard bees at the hive entrance. Depending on the season, it sometimes attracted them and sometimes repelled them. When added to sugar water for foraging bees, it had a repelling effect [8].
In 2012, Papachristoforou and colleagues showed that 2-heptanone, released from the jaws when biting, acts as a local anesthetic. It paralyzes small arthropods like wax moth larvae and varroa mites. Its effect is said to be similar to lidocaine [7].
This does not prove that 2-heptanone has nothing to do with alarms, and the debate continues. But we now know it is a substance whose role is more than just being an "alarm component."
4. Does smoke erase the bees' alarm smell or dull all smells?
Beekeepers often blow smoke into hives before opening them. There are several experiments about how this calms bees.
Visscher and colleagues (1995) studied electrical signals in bee antennae that respond to smells. They found that when smoke was present, the antennae’s reaction to both isoamyl acetate and 2-heptanone dropped. The reaction to flower scents (phenylacetaldehyde) also dropped similarly. The reactions returned to normal after 10 to 20 minutes [4]. This experiment showed that smoke temporarily reduced the antennae’s response to smells other than just the alarm.
Gage and colleagues (2018) used smoke from burlap and spent hops on bees stimulated by electric shocks. The smoke did not much change the chance of a bee extending its stinger. However, it lowered the chance that venom drops would appear at the tip of the sting. A hypothesis suggests these drops might help spread alarm pheromone [9].
How smoke works is not fully settled. It may dull smell responses or reduce venom drops. Also, electric shocks are not a natural situation for bees.
5. Do flower scents hide the alarm smell or signal food?
In 2015, Nouvian and colleagues reported that linalool and 2-phenylethanol, common in flower scents, suppressed aggressive reactions caused by alarm pheromone. This worked similarly to lavender scent [1].
In this experiment, bees were irritated by a device spinning wings, and the number of stinging attacks was counted [1].
The reason is interesting. It is thought that flower scents did not just hide the alarm smell. Instead, bees reacted strongly to signals indicating food value, which took priority over the alarm [1].
This finding might help beekeepers keep hives calm. However, practical applications are not yet established.
6. How to watch bees safely and learn about their sense of smell
You can observe bees from a distance. If you see honeybees on flowers in a garden or park, do not approach them. Keep your distance and just watch. Looking at how long they stay on each flower or which way they fly away is enough. Do not touch them, chase them, or get close to their nest. If you are worried about being stung, it is okay not to go near them.
You can also look into books for more information. The reason smoke works has several theories and is not yet decided [4]. Try finding beekeeping books in the library. Compare how they explain the use of smoke. You may see differences between scientific research and practical field language.