Last week, I began a discussion about smell. Today, I’d like to talk a little about the role of smell in the lives of our flora and fauna, and how the sense of smell has long been in decline in humans. I will also conclude my list of signature scents of the seasons.

Smell plays a huge role in plant and animal communication. However, nearly all of these airborne messages go undetected by the human nose. Smell is the principal means by which insects communicate, be it ants laying down scent trails for other ants to follow or the ability of a male Cecropia moth to find a female several kilometres away by following the scent of pheromones she emits. Salamanders depend on smell each spring when they follow their imprinted memory of their natal forest pond with its specific odours of mud and decaying vegetation. Smell allows squirrels to find acorns they buried months earlier, while wolves, by scent alone, can locate prey, other pack members and enemies. Even though birds in general have a poor sense of smell, turkey vultures are an exception. They can use the odour of rotting meat to find a dead animal deep in the forest. In the plant world, petunias emit a strong odour at night specifically to draw in hawk moths for the purpose of pollination. A host of other plants, when under attack by insects, will emit aromatic substances that serve to attract insect eaters. When it comes to humans, however, the role of smell as a tool of communication – and the acuity of our sense of smell itself – has been deteriorating for thousands of years.

Evolution has long been phasing out our sense of smell. Genetic studies have shown a steady decline in the number of functional olfactory receptor genes through primate evolution to humans. These are the genes that encode for the production of receptor cells in our nose that detect different odours. Today, even mice have 2.7 times as many functional olfactory receptor genes as humans! Fully 70% of the human olfactory receptor genes have become nonfunctional. Clearly, human evolution has been marked by the gradual rise of vision and the reduction of smell. Our noses have become smaller and our eyes have moved to the middle of the face to permit depth vision. At the same time, the adoption of an erect posture has moved our nose away from the ground and away from its multiplicity of odours. Despite this decline, we still crave smell today. This helps to explain why chemists continue to drench everything, from cars to lotions to incense, with some kind of chemical scent.

Many questions remain as to why humans find some smells pleasant and others disagreeable. For example, why do we find the smell of rotting meat so foul? Once again, is there an evolutionary advantage to being repulsed by this smell? The standard response would be that evolution has shaped us to avoid eating things we don’t like the smell of because they are probably unsafe. Another question could be: Why do humans find the smell of most flowers pleasing? Is there something in our evolutionary history that makes liking floral fragrances important to our survival, or is there no connection at all?
The smells listed below are representative of spring and summer in the Kawarthas. They are listed more or less in chronological order. Many, however, continue to occur over more than one season.
Early spring  

·          Making maple syrup – the sweet aroma of evaporating sap, mixed with the smell of wood smoke, wafting from the sugar shack

·         Grass fires – a common April smell in suburban Peterborough in the 1950’s and 60’s.

·         Thawing earth – as microbial activity increases in the spring, hundreds of chemicals are released by the microbes in the soil. The rich, earthy smell of the ground at this time of year is usually due to a compound called geosmin. It is also what gives beets their earthy taste. The human nose is extremely sensitive to geosmin.
·         Last falls’ leaves and grass – the smell of decomposing leaves from the previous fall,  heated and dried on a warm spring day,
·         Earthworms – the fishy, musky smell of earthworms slowly simmering in the sun-warmed water of sidewalk puddles after an overnight rain
·         Wild leek – the onion-like smell of wild leek below your feet during a spring walk through a maple woodlot. Their leaves are the first new growth of spring and appear soon after the snow melts.
·         Skunk cabbage – even though this species has not yet extended its range northward into the Kawarthas, it may soon do so as a result of climate change. In southern Ontario, skunk cabbage is the first flower to bloom in the spring. Carrion- eating insects are attracted to the smell and color and therefore play the role of pollinators. The skunky odour is spread to a large degree by the heat generated as the plant grows. It can even melt the snow that comes into contact with the plant.

Mid to late spring 

·         Freshly mown grass –    a researcher in Australia, Dr. Nick Lavidis, has found that a chemical released by freshly mowed grass can help people relax, put them in a better mood, and actually enhance memory. Like other smells, it directly affects the brain’s emotional and memory structures.

·         Balsam poplar – from early May to mid-June, this sweet, pungent balsam odour permeates the air almost everywhere in the Kawarthas. It is especially strong on warm, damp mornings. The scent originates from the sticky sap that oozes from balsam poplar buds as they open. Balsam poplar is probably my favourite smell of the year and says “this is springtime in the Kawarthas” more than any other odour.

·         Lilac – in the second half of May, city neighbourhoods and rail-trails are drenched with the floral fragrance of lilac. Even though I’m generally not a fan of non-native species, I’m ready to make an exception for lilacs!

·         Cherry – In the countryside, pin and chokecherry add their fragrances to the mix of lilac, balsam poplar and freshly mown grass. Take a moment to smell chokecherry blossoms close up. They have a lovely almond smell, as do the twigs and bark when crushed.

·         Other trees, shrubs, vines, and wildflowers – sweetgale (sweet and spicy leaves),  black locust  (in addition to their rich, floral smell, the flowers are edible), wild grape flowers (a clean, refreshing fragrance), red trillium (a carrion-like smell that attracts pollinating flies)


Early summer 

·         Freshly cut hay curing in the sun – the sweet scent of the first days of summer. It is claimed that from a downwind location, you can smell a hayfield a mile away.

·         Common Milkweed – if you come across a patch of milkweeds in July, stop to smell the honey-sweet perfume of the mauve-pink flowers which fills the air along country roads. The flowers can even be dried and used for making pot-pourri.

·         Canada elderberry – the fragrant, tiny white flowers of the elderberry shrub occur in flat clusters. They not only smell great but they are also edible. When flowers are open, the clusters can be picked, dipped in pancake batter and fried.

·         American basswood – in early July, the powerful, honey-like scent of blooming American basswoods can fill the air over large distances. The flowers attract over 60 species of insect pollinators, especially honey bees. In fact, the basswood is sometimes called the “bee tree,” in reference to the huge swarms of bees that can make the tree come alive with their humming. The nectar of basswood flowers produces a strongly flavoured white honey. The flowers can also be gathered and dried to make tea. Basswood is sometimes referred to as “linden.”

·         Summer leaves  –  stop and rub the leaves of the following plants for the wonderful cornucopia of smells they release: catnip (mint-like), wild bergamot (the peppery, citrus-like aroma of Earl Grey tea), yarrow  (pungent, sage-like),  aniseroot (licorice-like), and prickly-ash (lemon)

·         Mayapple fruit – our ancestors would dry the apple-like fruits of the mayapple, a spring wildflower with a large, umbrella-like leaf,  and use them to give a pleasant, lemony smell to stored clothing and bedding

·         Approaching rain – even though they’re probably only sensing a change in air pressure and humidity, some people claim they can actually smell rain before it arrives


Late summer

·         Petrichor – this is the strong scent in the air when rain falls after a dry spell of weather. The smell comes from oils given off by certain plants during dry periods which are absorbed by the soil. When it rains, the oil is released into the air along with geosmin (see Early Spring) which produces the distinctive scent.


·         Walnuts – the strong, citrus smell of unripe, green-coloured walnut fruits is a sign that summer is starting to wane. Keep one in your hand or pocket when out for a walk, just to enjoy the scent.

·         Sweetfern – the shiny, fern-like leaves of this Shield plant are incredibly aromatic, especially on a hot day. The leaves keep their scent for months after being picked.

·         Goldenrod – a subtle but sweet smell of goldenrod is everywhere by late August when entire fields become a sea of yellow.

·         Algal blooms – in addition to turning the water milky-green and smelling bad, algal blooms usually mean that Labour Day is quickly approaching and, with it, the beginning of the true New Year.


Try to take time to cultivate your sense of the smells of the season. An awareness of their presence and where they are coming from can add so much to an outing or to just spending time working in the yard. Be it fallen leaves in November, skunk spray in February,  balsam poplar in May or wild bergamot in July, smell never ceases to inform us about what is happening in the natural world.



Categories: Columns

Drew Monkman

I am a retired teacher, naturalist and writer with a love for all aspects of the natural world, especially as they relate to seasonal change.