20th May is World Bee Day, the aim of which is to raise awareness of the importance of bees and beekeeping. So, hey, let’s do that!

I’m helped this month by my horticulturist* dad who, while working in a public garden recently, discovered this honeybee swarm in a honeysuckle. (Me: “what sort of tree is that?” Dad: “a winter flowering Honeysuckle lonicera. It’s a shrub, not a tree!” Yes, despite his tireless efforts I’m still pretty clueless about plants.)

Now, Dad knows what he’s doing in such situations. He immediately called the professionals. One does not mess around with (or ignore) a swarm of bees – one finds a beekeeper, stat. Obviously bees can sting, but they’re also endangered and they need to be collected to protect them. Should you find yourself in such a situation, you can find someone local via the British Beekeepers Association website.

That out of the way, aren’t they gorgeous? A swarm like this is a natural phenomenon, that happens when new queen bees are born and raised in the colony. Worker bees stop feeding the old queen – because a laying queen is too heavy to fly – and then in time she leaves with a swarm. They cluster somewhere, as you see in the photo, while scout bees go looking for a new location to settle. Bees in swarms only have the honey or nectar in their stomachs to keep them going, so they’ll starve if they don’t find a new home, and nectar, quickly.

This is all fascinating, of course, but what does it have to do with chemistry? Well, quite a bit, because bees are brilliant chemists. Really!

Ethyl oleate is an ester and an important chemical for bees (image source)

Firstly, despite what DreamWorks might have taught us, bees don’t have vocal cords, and they don’t sound like Jerry Seinfeld. A lot of their communication is chemical-based (actually, it turns out this is a topic of hot debate in bee circles, but since this is a chemistry blog, I’m not doing waggle dances. No, not even if you ask nicely).

As you might imagine, there are multiple chemicals involved, and I won’t go into all of them. Many are esters, which are known for their sweet, fruity smells, and which are also (at least, the longer-chain ones) the building blocks of fats.

One such chemical is ethyl oleate which plants produce and which, interestingly, we humans also make in our bodies when we drink alcohol. Forager bees gather ethyl oleate and carry it in their stomachs, and they then feed it to worker bees. It has the effect of keeping those workers in a nurse bee state and prevents them from maturing into forager bees too early. But, as forager bees die off, less ethyl oleate is available, and this “tells” the nurse bees to mature more quickly – so the colony makes more foragers. Clever, eh?

In this situation, ethyl oleate is acting as a pheromone, in other words, a substance that triggers a social response in members of the same species. Another example is Nasonov’s pheromone, which is a mixture of chemicals including geraniol (think fresh, “green” smell), nerolic acid, geranic acid (an isomer of nerolic acid) and citral (smells of lemon).

The white gland at the top of the honeybee’s abdomen releases pheromones which entice the swarm to an empty hive (image source)

An interesting aside: geranic acid has been investigated as an antiseptic material. It can penetrate skin, and has been shown to help the delivery of transdermal antibiotics, which are being investigated partly as a solution to the problem of antibiotic resistance. Nature is, as always, amazing.

Anyway, worker bees (which, again contrary to DreamWorks’ narrative, are female) release Nasonov’s pheromone to orient returning forager bees (also female) back to the colony. They do this by raising up their abdomens and fanning their wings. Beekeepers can use synthetic Nasonov pheromone, sometimes mixed with a “queen bee pheromone” to attract honeybee swarms to an unoccupied hive or swarm-catching box.

As my Dad chatted to the beekeepers (partly on my insistence – I was on the other end of my phone texting questions and demanding photos) one substance they were particularly keen to mention was “the alarm pheromone,” which “smells of bananas.”

Ooh, interesting, I thought. Turns out, this is isoamyl acetate, which is another ester. In fact, depending on your chemistry teacher’s enthusiasm for esters, you might even have made it in school – it forms when acetic acid (the vinegary one) is combined with 3-methylbutan-1-ol (isoamyl alcohol).

Never eat a banana by a bee.

Isoamyl acetate is used to give foods a banana flavour and scent. But, funnily enough, actual bananas you buy in the shops today don’t contain very much of it, the isoamyl acetate-rich ones having been wiped out by a fungal plague in the 1990s. This has lead to the peculiar situation of banana-flavoured foods tasting more like bananas than… well… bananas.

Modern bananas can still be upset bees, though. There are numerous stories of unwary individuals who walked too close to hives while eating a banana and been attacked. So, top tip: if you’re going on a picnic, leave the bananas (and banana-flavoured sweets, milkshakes etc) at home.

The reason is that banana-scented isoamyl acetate is released when honeybees sting. They don’t do this lightly, of course, since they can’t pull out the barbed stinger afterwards, and that means the bee has to leave part of its digestive tract, muscles and nerves embedded in your skin. It’s death for the bee, but the act of stinging releases the pheromone, which signals other bees to attack, attack, attack.

One bee sting might not deter a large predator, but several stings will. Multiple bee stings can trigger a lethal anaphylactic reaction, known allergy or not. So although utilising their stingers causes the death of a few (almost certainly infertile) bees, the rest of the colony (including the fertile individuals) is more likely to survive. From an evolutionary perspective it’s worth it – genes survive to be passed on.

Isoamyl acetate is an ester that smells of bananas, and is an alarm pheremone for bees (image source)

Moving on, I obviously can’t write a whole blog post about bees and not mention honey! We take it for granted, but it’s amazingly complicated. It contains at least 181 different substances, and nothing human food scientists have been able to synthesise quite compares.

In terms of sugars, it’s mostly glucose and fructose. Now, I’ve written about sugars extensively before, so I won’t explain them yet again, but I will just reiterate my favourite soap-box point: your body ultimately doesn’t distinguish between “processed” sugars in foods and the sugars in honey. In fact, one might legitimately argue that honey is massively processed, just, you know, by bees. So, you want to cut down on your sugar intake for health reasons? Sorry, but honey needs to go, too.

Honey is actually a supersaturated solution. In very simple terms, this means there’s an excess of sugar dissolved in a small amount of water. One substance which bees use to achieve this bit of clever chemistry is the enzyme, invertase, which they produce in their salivary glands. Nectar contains sucrose (“table sugar”) and, after the bees collect nectar, invertase helps to break it down into the smaller molecules of glucose and fructose.

“Set” honey is honey that’s been crystallised in a controlled way.

That’s only the beginning, though. There are lots of other enzymes involved. Amylase breaks down another sugar, amylose, into glucose. And glucose oxidase breaks down glucose and helps to stabilise the honey’s pH. One of the molecules produced in the reaction with glucose oxidase produces is hydrogen peroxide, which yet another enzyme, catalase, further breaks down into water and oxygen.

Bees regurgitate and re-drink nectar (yes, I suggest you don’t overthink it) over a period of time, which both allows the sugar chemistry to happen and also reduces the water content. When it’s about one-fifth water, the honey is deposited in the honeycomb, and the bees fan it with their wings to speed up the evaporation process even further. They stop when it’s down to about one-sixth water.

As I said a moment ago, honey is a supersaturated solution, and that means it’s prone to crystallising. This isn’t necessarily bad, in fact, “set” honey (my personal favourite) is honey which has been crystallised in a controlled way, so as to produce fine crystals and a creamy (rather than grainy) product.

The formation of a new honeycomb.

The potential problem with crystallisation is that once the sugar crystals fall out of solution, the remaining liquid has a higher-than-ideal percentage of water. This can allow microorganisms to grow. In particular, yeasts can take hold, leading to fermentation. Honey left on the comb in the hive tends not to crystallise, but once it’s collected and stored, there’s a greater chance that some particle of something or other will get in there and trigger the process. It helps to store it somewhere above room temperature. And honey is naturally hygroscopic, which means it absorbs water. So store it somewhere dry. In short, never put honey in the fridge.

Speaking of yeast and heat, heating changes honey and makes it darker in colour, thanks to the Maillard reaction. Commercial honey is often pasteurized to kill any yeast, which improves its shelf life and produces a smoother product. Also, because honey is naturally slightly acidic (around pH 4), over time the amino acids within in start to break down and this also leads to a darkening of the colour.

One more important safety concern: honey, even when pasteurized, can contain bacteria that produce toxins in a baby’s intestines and lead to infant botulism. So, never give children under one honey. It’s not a risk for older children (and adults) thanks to their more mature digestive systems.

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Back to Dad’s bees! They were collected in a transport box by two local experts, Sharon and Ian. The bees march into the box two-by-two, wafting Nazonov’s pheromone to signal that this is home. From there, they were safely transferred to a new, wooden hive.

There’s only one way to finish this post, I think, and that’s with one of my all-time favourite Granny Weatherwax moments:

‘Your bees,’ she went on, ‘is your mead, your wax, your bee gum, your honey. A wonderful thing is your bee. Ruled by a queen, too,’ she added, with a touch of approval.

‘Don’t they sting you?’ said Esk, standing back a little. Bees boiled out of the comb and overflowed the rough wooden sides of the box.

‘Hardly ever,’ said Granny. ‘You wanted magic. Watch.’

Happy World Bee Day, everyone and, as always, GNU Terry Pratchett.

* Dad was unsure about the label “horticulturist” but I pointed out that the definition is an expert in garden cultivation and management, particularly someone’s who’s paid for their work. All of which he is. He replied wryly that, “x is an unknown quantity, and a spurt is a long drip.” Love you, Dad x 😄

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