Famous French entomologist Jean Henri Fabre in the 1870s discovered something by accident that fascinated him. In the serenity of his house, well screened by trees, Fabre found a female great peacock moth had emerged from a cocoon that had been lying on the table. He had no plans for the moth, but out of habit, he placed a wire cage over it. He was soon surprised to find giant peacock moths taking over the entire house. With a soft flick-flack of wings, the male moths were mobbing the cage, jostling with each other to get close enough. But how did they know that the female was there? How did they find their way in the dark? Fabre observed that whatever the female moth touched with her fat belly had some fluid and he said to himself, “There you have her bait, her love-philtre.” The moths could smell the liquid through their big, feathery antennae. It was not until 1959 that the German scientist Adolf Friedrich Butenandt identified the smelling liquid as an insect sex pheromone that males could detect from over 10 kilometres away!
A male moth would encounter a female moth’s pheromones, then fly towards the female in a zigzag path following the female’s pheromones, using its large hairy antennae and narrowing its zigzag as it got closer to the female. The pheromone molecules diffuse through open pores in the hair on the moth’s antennae and reach a receptor protein in the membrane. This produces an electric charge leading to a nerve impulse, which is sent to the brain. It acts like Cupid’s arrow!
The male honey bee, on the other hand, is quite a romantic at heart. He leaves love letters for his sweetheart. In the springtime, you will see him touch a tree’s bark here and then fly away to touch another bark there. Like this he moves to eight or nine trees and then comes back to the first tree and starts again. For many years, people had no clue why the bees behaved the way they did, until researchers recently found that the male bee leaves a letter for the female bee utilising this technique. It does not have ink to draft the letters but what it has is no less.
In its jaw, it has a gland that secretes something similar, the difference being that it’s an odorous liquid that the male bee secretes. This liquid functions like ink and the jaws work like pens! After touching the tree bark and biting the leaves, the male leaves behind its scented letter. He continues doing this till he finds his lady love. By that time, the lady bee has already read his letters and will be waiting for him.
One particularly gripping instance of such pheromones among insects is the case of fruit flies. In 2007, researchers from the University of Michigan discovered that male fruit flies showed a decreased lifespan simply by smelling and not coming in touch with the female fruit flies. Yes, that’s right — smelling the opposite sex shortened the lives of the males. This is because male flies store less fat, starve, age faster and die quicker after detecting the female’s scent.
Another twist in the story comes with the tale of the male mealworm beetle. After a male mates with a female, the former spreads a pheromone over the latter discouraging other males from trying to mate with the same female. This conserves the energy of the female. Another clever development in the insect world is that of certain spiders producing a pheromone identical to the sex attractant of a female moth. This attracts nocturnal male moths which, when they navigate to the source of the pheromone, are captured by the spiders. Talk of femme fatale!
Usage of sex pheromones has also been found to be important in the love lives of certain amphibians like the African clawed frogs and American toads. They secrete a bouquet of these chemical substances from a gland underneath their thighs into the surrounding water. Some like newts and salamanders, use their tails to fan the bouquet towards the females.
Have you also been told how men fall in love with a woman and get into horrible fights? Similar instances happen in the lizard world. Male lizards lure females to their territories through the scent marking of food. Many female lizards are usually interested in the quality of the territory that the male defends rather than the male himself. This increases competition among the males because all the males want to occupy favourable areas with many sources of food to attract the females.
Lizards use scent marking to determine either the quality of the male occupying the area or the resource richness of the area. Females of the Carpetan rock lizard prefer pheromones produced by older males as they are able to produce more pheromones than younger ones. Now, who said humans were the only ones who were finicky?