Dear Blue Lobster:
i caught a rusty crayfish and my cousin says its red because it is in hot water. i think it's red because its parents were red. my paw paw says it's because god made it that way. who's right? what makes a rusty crayfish red?
Dear Gentle Sir:
The Rusty Crayfish (Orconectes rusticus) is red because that is its natural colour morph; that is, it is red due to its genetics just as your skin colour was inherited from your parents and their parents, etc. This is called a heritable trait.
Orconectes rusticus became red, however, because its ancestor habited areas with high concentrations of ferrous oxide, commonly known as rust, in the water. Because of this the Orconectes expressed red and orange colors and since they matched the environment better these colour morphs eventually became endemic to their population. This resulted in the speciation of rusticus.
Today you can hunt Rusty crayfish with a metal detector thanks to their high iron content and doctors often prescribe the species to anaemic women during pregnancy as well. One may even find carnival-goers during the Mardi Gras dressed in costumes made of scrap metal painted red replete with refrigerator magnets honouring bebe rouillé, the little red bug.