"I am calling you-ou-ou-ou-ou-ooo!"

Whether bringing individuals together from miles away or from right next door, sending and receiving chemical signals is the oldest form of communication on the planet. Whether secreted from skin, tongues, or glands, sexual "pheromones"  -- wafted through the air, suffused in water, or deposited on the ground -- send their distinctive "come hither" message to the opposite sex:"I am ready. Now!"

The word ‘pheromone' comes from the Greek, pherin, to transfer, and hormon, to excite or stimulate. While pheromones perform a variety of functions -- like identifying male territory, and warning away rivals -- sexual pheromones are designed to attract and arouse the opposite sex.

How it works

Animals produce hormones. When secreted externally they become pheromones. The "scent" is received by the opposite sex through the ‘vomeronasal organ,' a part of the olfactory system -- the system by which animals smell things and get their brains stimulated.

The effects of all this olfactory ‘Morse Code' are as diverse as the animals that employ it, as these examples show:

• Female pigs become sexually aroused by the sex pheromones in the saliva of male pigs.
• Golden male hamsters are stimulated to mount females after getting a whiff of vaginal pheromones.
• Female goldfish release their pheromones into the water at night, and the males, picking up the scent, find themselves producing sperm for fertilization. The next morning, when the females are ready to spawn, the males enthusiastically make the journey in search of the goldfish beauties with that alluring scent. However, it's a little disconcerting to discover that all the guys in the neighborhood are making the same commute.

That signature scent

Part of the work of sex pheromones is to help members of the same species identify each other, so it won't be a waste of time to have sex.

For instance, there are thought to be 150,000 to 250,000 different species of moths, but there is only one particular, chemically correct, sexual pheromone per species. A male silk moth will receive a female's sexual invitation from as far away as seven miles, but he won't bother to waste his time and energy flying over -- making himself vulnerable to predators and competing with all the other males she is beckoning to -- unless the pheromone is from a female of his own kind. When the right call gets the attention of the male's antennae, it's then pretty much irresistible.

How about them red garter snakes?

Nature is never satisfied until a species evolves the best strategy for mating and surviving. So it should come as no surprise that some animal groups will break or bend the pheromone attraction rules.

Take the case of the Manitoba red-sided garter snake. Some males mimic the pheromones of the females, thereby tricking other males into trying to have sex with them. Yes, that's right; they become "she-males."

Manitoba garter snakes spend the entire winter in the frigid Canadian region between Lake Manitoba and Lake Winnipeg, arriving by the thousands, after slithering their way over miles of rocky terrain. Males and females hibernate together in crevasses as small as six feet wide and sixteen feet deep to keep from freezing to death. When spring arrives, each den disgorges as many as 10,000 snakes. The males are the first to emerge from their winter retreat. When the females finally appear, seething balls of hundreds of male snakes form around one female. These snake balls remain intact, rolling around the rocky terrain until one male has successfully mated with the female.

Trick or treat?

Here's the interesting part. Some mating balls have no female. In that writhing horde of snakes, the only way a male can identify a female is by her pheromones, secreted through her skin. Snakes flick their tongues in and out, picking up chemical cues from the air, and transfer them to a sensory organ in the roof of their mouth.

So, why would any self-respecting male garter snake become a she-male? One theory is that this subterfuge keeps the other males from "getting the girl" and passing on their genes. They're all busy mistakenly trying to mate the imposter.

Are we at the mercy of our body chemistry?

Do humans also emit and receive pheromes? Do we "smell" as good as the rest of the animal world? To find out you'll have to read my next Animal Sex blog-"The Scent of a Woman." [LINK to the blog]

Coming Attractions

Next up on Birds Do It, Bees Do It, you'll read about a sea creature with a penis that can grip like a hand. "What is tugging on my leg? Oh noooo..."

Reviewed by John A. Bukowski, DVM, MPH, PhD and Susan E. Aiello, DVM, ELS

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