Animals
Animals are multicellular eukaryotes with differentiated tissues. They rely on plants, microbes, or other animals for food. Animals are usually self-mobile in at least one phase of their life cycle.
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Important Animals for Martian Colonization
Certain types of animal may be of great importance for settlements.
Use of animals as food sources is open to ethical debate. The Feed conversion ratio (FCR) is a measure of efficiency in conversion from vegetable sources to edible meat. Proteins are an essential part of the human diet. These may come from plants, of from animals by conversion of plant carbohydrates into meat.
Insects
Most insects are not vital for a colony, but some may be important. If soil based agriculture is used on Mars, insects are part of the complete ecosystem required for soils and plants. Earthworms are often used in soil production and as a part of agricultural soil. They in turn require bacteria in the soil to feed themselves.
Pollination
Pollinators, such as moths, butterflies, and bees, are a critical part of agriculture. Small greenhouses may be able to accommodate pollination needs by direct human action. More efficient means, such as natural pollination, are needed for large greenhouses. Bees also produce honey and wax as a by-product.
Food
Other insects, such as mealworms, silkworms[1], or crickets may be raised for food. The FCR is high and they may be fed biomass that is not digestible by humans.
Natural Fiber
Silkworms generate silk, but require a diet of fresh mulberry leaves. This seems unlikely to be used on Mars until the settlements grows very large and there is demand for luxury products.
Arachnids
Spiders are a source of natural fiber - spider silk. However, this is not a commercially viable product on Earth, so even less likely on Mars.
Fish
Species of fish such as tilapia and catfish can be fed on biomass, and may provide a source of food and amusement.
Mammals
Humans are the most important mammal to Martian colonization. Other mammals, such as rodents, cats, and dogs may be brought to Mars as pets.
Mice and Rats can serve a triple role - food, research subjects, and pets. Rabbits and other mammals can serve as sources of meat.
Birds
Birds can serve as pets, elements of a biosphere in a settlement and as food. Eggs can serve as food as well. Chicken have a high FCR, and can be fed from biomass that is not edible by humans.
