Excerpt from Valley 101: A Slightly Skewed Guide to Living in Arizona, a collection of Clay Thompson’s columns for The Arizona Republic. (Originally published October 22, 2002.)
Q: My husband and kids were out hiking and stopped at a stock tank to look for animal tracks. In the water, they saw these amazing prehistoric bug-looking things. They have a horseshoe-shaped shell with what looks like eyes on it. From under the open end of the shell, there is a tail with a forked end.When you flip them over, they have a dark-orange fringe that looks like millipede legs. What is it?
A: Ooo. Ooo. Ask me. Ask me. I know this one. Ask me. I am soooo smart.
I actually did know this one, but just to be sure, I doubled-checked in my handy Insects of the Southwest by good old Floyd Werner and good old Carl Olson. What these people found in the stock tank was one of the desert’s most interesting creatures: tadpole shrimp. Crustaceans in the desert. Who would have thought of that? Isn’t that great?
Tadpole shrimp, and their cousins fairy shrimp, are not especially closely related to honest-to-goodness shrimp, and in the fossil record, they appeared about 100 million years before shrimp. In fact, they were here before the dinosaurs.
Tadpole shrimp live in stock tanks or desert waterholes. Their eggs can remain viable for a long time if the tank or waterhole dries up.
When the water returns, tadpole shrimp hatch, develop, eat a lot, mate, lay more eggs, generally tear up the pea patch and then die in a space of about 30 or 40 days.
They thrive in the mud at the bottom of a tank or pond, which they churn up as they feed on the microorganisms they find there.
They have very sturdy jaws and will eat plants and animals, and sometimes each other. Fairy shrimp are much smaller, and you can almost see through them. Females have a bulge in their middles, the egg sac. Also, they swim upside down. I don’t know why.
So if they are so tiny and only live a few weeks in the confines of a pond or tank, how is it that they are so widespread? I’m glad you asked. It’s because their little teeny-tiny eggs get carried from place to place on the mud sticking to the feet of birds. Cool.