Bigger antennae means better reception.

The biggest insect that I have ever found in nature was a female polyphemus moth. Males are smaller than females; a large female can have a wingspan of up to six inches. Polyphemus moths belong to the silk moth family. The largest moth in North America is the cecropia moth, a close relative of the polyphemus moth, and has a wingspan of up to seven inches. The silkworm moth Bombyx is grown commercially in China and used for the production of silk fabric.

Even though male polyphemus moths are smaller than females by a large margin they make up for it in the size of their antennae. All insects use their antennae for gathering chemical information about the world around them. Moths do the same thing, but the males of some species take this to an entirely new level. They use their large and impressive array of chemical-receptors to find females.

Female polyphemus moths, like many of their kind, secrete a chemical agent called a pheromone. They are active at night and will release two different chemicals (to see more information, click here) to attract a mate. The chemicals (bombykol and bombykal - click here to see its chemical formula) are long-chain carbon alcohols that are very volatile and disperse easily in the air. A single molecule coming into contact with the multitude of receptors on the male's antennae will elicit an electrical signal to the creature's brain and produce a reaction. The ratio of the two pheromones and their concentrations appear to be significant in how it affects the male's behaviour.

It is interesting to note that the male moth's sensitivity to these pheromones is about on par with the sensitivity a dog's nose shows to any particular scent. Put another way, the male moth can detect concentrations of the pheromones as low as around 12 ppb (parts per billion) and represents an amazing ability regarding detecting and directing behaviour. Depending on atmospheric conditions, a male can detect the presence of a female up to several kilometers away.

I am always amazed at the way nature solves problems. There are many examples of this kind of interaction within a species and between species, and our knowledge of them has barely scratched the surface. The study of biology goes way beyond gross morphology. As Ian Malcom said in the film Jurassic Park, "Life will find a way."

Thanks for reading.     Ericspix     Eric Svendsen