Season 8 Episode 17 | 4m 42s | Video has closed captioning.
Tadpole shrimp are neither tadpoles nor shrimp. They’re time-traveling crustaceans called triops. Their eggs can spend years – even decades – frozen in time, waiting to hatch. When California rice growers flood their fields, they create the perfect conditions for hordes of these ravenous creatures to awaken.
Aired: 10/12/21
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This tadpole shrimp is coming for your rice.
Hungry hordes of them find their way into the rice fields of California’s Central Valley and go to town munching on the young seedlings.
But where did they come from, with the ocean so far away?
A couple of weeks ago, this was just a dry dusty field.
Turns out they were here all along.
They’re time travelers waiting for months, years, even decades in the sun-baked soil.
Each spring, when rice farmers flood their fields and scatter their seeds they inadvertently create the perfect conditions for billions of tadpole shrimp to awaken.
The egg’s rugged outer shell called the chorion cracks open and the larva wiggles its way out of a translucent sac.
Tadpole shrimp aren’t really tadpoles, they aren’t even shrimp, though they are crustaceans whose ancestors evolved in the sea.
The tiny larvae forage through the mud incessantly for any food they can dig up.
They’re not picky.
But as they grow they really acquire a taste for rice plants.
They chomp away at the first tender roots and leaves just when the seedling needs them most.
Without roots to hold them down the young plants just float away.
And if it loses its first leaves a seedling can’t get enough energy to grow.
As if that’s not enough, the throngs of tadpole shrimp stir up the mud, blocking out the sun.
But the rice plants that do manage to break the water’s surface are safe.
Their roots and stems are thick and tough enough that the tadpole shrimp leave them alone.
At that point tadpole shrimp are actually kind of helpful.
They turn their appetites to any weeds that make their way into the rice field.
They even eat the larvae of mosquitoes that could carry West Nile virus when they grow up.
Once the tadpole shrimp mature, they lay their eggs in the mud and then they’re done.
Adult tadpole shrimp only live for about a month.
The secret to these armored arthropods' survival is their eggs.
At the end of the growing season, farmers drain their fields so they can harvest the rice on dry ground.
No water?
No problem.
The eggs can survive being completely dehydrated for years.
Their tough outer shell protects them from scorching heat, freezing cold, even time itself.
The embryos inside just stop developing.
They enter a suspended state called diapause.
That’s what keeps them from hatching in a dry field.
When the water returns, and conditions are right again, they’ll be ready to hatch.
That’s because tadpole shrimp evolved to live in temporary freshwater ponds, created by seasonal rains throughout North and South America.
It’s how they endure having their ponds dry up each year.
They’ve been living this way for hundreds of millions of years-- since before the dinosaurs-- waiting out droughts, changing climates, even global catastrophes.
