Animal Life Spans

by Dennis E. Figg
photography by Jim Rathert

Just how old is "old" if you're an animal?



When Grandma Figg turned 90, our family gathered for a big celebration. Ninety years is a long time. Ninety years is really old. Just ask Grandma!

Many animals live a long time. However, old is different for different kinds of animals. No robin, frog or skunk can expect to live as long as a human. Yet these animals usually outlive mice and grasshoppers. And grasshoppers are ancient compared to mayflies.

Have you heard that mayflies live only one day? Actually, they live many months at the bottom of a stream, but they molt - or change - into a short-lived adult. Their only assignment is to mate and lay eggs, so most individuals live just a few hours. Fortunate individuals live a few days.

Next time you see a grasshopper, take a hard look at it. Does it look old? It only takes one summer for a grasshopper to emerge from an egg, grow into an adult and live a lifetime. Unless it gets eaten by a bluebird or blown into a pond and becomes bass food, the grasshopper can expect to live a few months. Old grasshoppers die with the first hard freeze of autumn.

Small irds like robins or bluebirds are old at five to six years. The may fly will only live a few hours or days as an adult.

Bluebirds feed on grasshoppers and mayflies. Bluebirds that hatch this summer grow quickly and may even raise a family of their own next year. Three-year-old bluebirds are probably old. Bluebirds that survive five to six years are old.

Bass eat insects that fall into their pond. Fingerling - or young - bass grow fast the first year or two, but even the largest lunkers probably live only six to eight years.

The bullfrog sitting at the edge of the pond may outlive both bluebirds and bass. It took more than a year to transform from an egg to a froglet. With abundant food, most bullfrogs will grow fast and live two to three years. Fortunate individuals may live 10 years.

There are no rules about life expectancy, but there are some interesting trends. Generally, smaller species of animals within a group have a shorter life expectancy than larger species. Cricket frogs, for example, live only a couple of years, but bullfrogs may live a decade. A whip-poor-will lives two or three years. Bald eagles can live 20 years or more. A two-year-old minnow is old, but a flathead catfish can expect to live 20 years or longer.

The box turtle (bottom) and the hellbender (top) are examples of animals with slow metabolisms. They can live to 50. The grasshopper (middle) is ancient at two months. In Missouri, grasshoppers are killed by the first hard freeze.

Species that take a while to mature into adults tend to live longer than species that become adults quickly. Humans are a good example. Humans are "young" for more than a decade and do not mature until they are 15 years old, or older. With proper care and good health, humans can expect to live many decades.

On the other hand, cottontail rabbits stay with their mothers only a few weeks. Then they are on their own. Young-of-the-year rabbits are ready to breed and produce babies of their own in a few months. Most rabbits will only live a year or two. Robins, which can successfully raise a nestfull of babies in four weeks, live three or four years. Great horned owls, which spend the entire season raising a brood, may live 20 years.

Finally, animals with a slow metabolism tend to live longer than animals with a fast metabolism. Metabolism is the chemical and physical processes continuously going on in living organisms and cells. Shrews, for example, have a fast metabolism. They are short-lived. Shrews generally live a year or two. Turtles have a slow metabolism. The box turtle wandering through your neighborhood may be 45 years old. The freshwater mussel living in the bottom of an Ozark stream, filtering water and living a sedentary life, may be 100 years old!

This alligator snapping turtle can live past 100 years.

Are there animals that outlive humans? Hellbenders, the largest salamander in Missouri, may live up to 50 years. Really big catfish live a long time, perhaps matching the human life expectancy of about 70 years. Consider the alligator snapping turtle. Large individuals may grow to 200 pounds and take 100 years to get there. Lake sturgeon, probably the largest fish native to Missouri, can live to 150 years.

Some animals live a long time, though none of them will live as long as the oak tree in your backyard. People can expect to live, on average, a little more than 70 years. Fortunate individuals live well beyond that. Don't look now, but Grandma is showing her age!

Dennis E. Figg is natural history programs supervisor for the Conservation Department.