Summer is finally here! The sun is shining, the sky is blue and the temperature is rising. We all spend lots of lovely time outside enjoying the world we live in and enjoying nature. The problem with sharing with nature is that there are plenty of creatures that share a little bit too much. We’re talking about those pesky insects that turn you in to a meal! Talking of meals, we can use our sense of smell to help us sniff out a food place. These biting insects can do the same, sniffing out molecules to locate it’s human meal. If we want a way to keep these pests away we need insect repellent – and since one of their favourite smells is octenol, that’s a good place to start.

Something’s Bugging Me

We’ve all been there. A sudden itch leads to the discovery of a small, red bump. And once you’ve touched it, it only becomes more and more itchy. Oh look, there’s another one, and another one.

The common biters include mosquitoes, midges, gnats and horseflies. While we can get bitten at anytime, it always seems to be at night.

Why are people bitten more than others? How do other people always seem to avoid being bitten?

Blood, Sweat, and Tears

Let’s focus on mosquitoes, perhaps the most infamous of all the biting bugs! Mosquitoes have several ways to find a human. They can detect the heat from our bodies and even the carbon dioxide from our breath. They can also detect many compounds in our sweat, including octenol! Once a mosquitos finds us then it treats itself to a nice dinner of blood. We’ve talked about blood in one of our halloween Molecule of the Month posts!

A mosquito with a long proboscis. Mosquitos are deterred by the insect repellent octenol.
A mosqutio – the dreaded sight when you wake up in the morning because you know you’ll have a bite somewhere.

Hiding in Plain Site

Scientists believe that insect repellents reduce the volatility of octenol. Volatility is the fancy work for how likely and easily a substance will turn into a gas. A substance with high volatility is more likely to exist as a gas.

Reducing the volatility of octenol makes us less attractive to the biting insects. As mosquitoes find people by detecting compounds such as octenol, then repellents can make us invisible to them – even though we’re right there!

Mosquitoes to Mushrooms

Octenol is not just found in the insect repellent aisle, it is also known as mushroom alcohol. The smell of many mushrooms is because of this molecule.

A red mushroom with white spots
We haven’t installed the web plug-in for broadcasting mushroom odours through the internet yet – and companies haven’t started making a mushroom scented plug in air ‘freshener’ either. You’ll just have to imagine the scent.

All About Octenol

Octenol is an alcohol, which means it contains a hydroxy (-OH) groups. However, don’t confuse octenol and octanol! Even though they sound very similar, the structures of these molecules have one important difference!

All of the carbon atoms in octanol are bonded by a single bond. But in octenol, two of the carbon atoms are bonded by a double bond. This difference might seem small, but it can have a big impact on how these molecules behave.

We would be reticent not to point out that these are examples of ‘octanol’ and ‘octenol’ – and that there are many different ways of arranging eight (that’s where ‘oct‘ comes from) carbons with either all single bonds (this is what adds ‘an’ to the name) or with a double bond (which changes the ‘an‘ to ‘en‘) with a hydroxyl group in there somewhere! In this case the exact name for these is octan-1-ol and oct-1-en-3-ol. The numbers tell you where in the carbon chain the chemical groups are.

Octenol is a solid at room temperature and melts at 175 °C.

Recipe: Insect Repellent

In our bodies, octenol is produced from linoleic acid, with a little help from an enzyme or two. We obtain plenty of linoleic acid in our diets from oils, almonds and butter.

Outside of our bodies, there are a couple of different ways to make octenol in a lab. One is to take a molecule very similar to octenol and replace an oxygen atom, with the hydroxy (-OH) group. The other is a little more complicated and involves reacting two smaller molecules together to make octenol.

A Smelly Trap

So how can we use octenol as an insect repellent? We said right at the start that octenol is actually an insect’s favourite smell – so it actually attracts them instead. We can put the insect-attracting octenol to good use. If you can’t hide from the biting bugs, then why not give them another option… and then trap them! This is how octenol midge and mosquitos trap work. The device contains a large concentration of octenol that attracts the mosquitoes. However, when the mosquito reaches the device it either gets stuck on a sticky-pad and unable to move, or gets zapped with electricity.

Scratch and Sniff

It seems like octenol is a pretty annoying molecule, helping lure mosquitos to us! However, even without octenol, some insects still have other ways to find us! But, we can still use octenol to our advantage, trapping the biting insects before they find us!

If you want to play mosquito and try sniffing out octenol, then you might well find a mushroom!

But don’t let mosquitos ruin your summer! After all, the sun is still shining and the weather is still hot!

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