Iowa’s Living Fossil: a Bloodsucker that Calls the Mississippi River Home

When you think of ancient, blood-sucking creatures, your mind might jump to bats, leeches, ticks, or mosquitoes. Maybe even creatures of lore come to mind, like vampires, the chupacabra, or kappa.  But in the waters of Iowa's Mississippi River, a fascinating eel-like predator thrives. Dubbed a “living fossil” that hasn’t changed for millennia. This jawless fish is as ancient as it is unique.

Meet Iowa's Relic of the Past

The chestnut lamprey is a survivor from a time when dinosaurs still ruled the land, dating back to the dawn of time. As part of a group of jawless fish called agnathans, lampreys have changed very little, giving them their “living fossil” nickname. Their sucker-like mouths, filled with "sharp teeth," are what make them so distinct—and a nuisance to their fish hosts.

The Mississippi River, one of the world’s longest and most biodiverse waterways, is the perfect habitat for this ancient species. Though a single pre-1900 collection in the Des Moines River is the only occurrence of this lamprey from Iowa’s interior waters, the Mississippi remains their primary home. Seeing a chestnut lamprey is like glimpsing a relic of prehistoric times, a reminder of the ancient life forms that have thrived in our local waters for eons.

Nature’s Creepiest Bloodsucker

Unlike some lampreys that feed on particles in the water, the chestnut lamprey has a parasitic phase in it's life cycle. It attaches itself to larger fish, like carp, pike, paddlefish, or catfish, with its suction cup-like mouth and uses a rasping, "toothy" tongue to scrape through scales and skin, feeding on the blood of its host. While its feeding habits might sound menacing, lampreys rarely kill their host and are an important part of the river ecosystem.

The life of a chestnut lamprey begins in the riverbed, where its larvae, called ammocoetes, live for up to six years, burrowed in mud and feeding on organic debris. These young lampreys start out blind and toothless. Once they mature, they transform into their parasitic adult form and begin seeking out fish to attach to.

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Those things that look like teeth are actually there to hold onto the slimy fish, it's that rasping tongue that actually does the damage. Adults only live for about a year, but during this time, they play a crucial role in controlling fish populations in Iowa's rivers, weeding out the weak, sick, or injured fish.

Despite their gory feeding habits, chestnut lampreys aren’t invasive and are vital to the natural balance of the Mississippi River’s ecosystem. They help control the populations of larger fish and serve as prey for species like sturgeon and bass. They only grow to around a foot in length and won't harm humans at all (you are NOT their food). Unlike the destructive sea lamprey in the Great Lakes, the chestnut lamprey is a native species, well-adapted to its murky surroundings.

Protecting Our Lamprey

Anglers on the Mississippi River may find chestnut lampreys attached to game fish and incorrectly assume they are detrimental to the game fish populations. Actually, they are not, and please don't kill them! The Iowa DNR states, "the chestnut lamprey is endangered in Iowa, so if you catch one, release it unharmed immediately."

Additionally, chestnut lampreys are sensitive to water quality and habitat changes. Pollution, habitat loss, and dams can impact their populations, making conservation of their environment important for maintaining the health of Iowa’s rivers.

The next time you admire the Mississippi, remember that below its surface, the ancient chestnut lamprey continues its life cycle, quietly maintaining the balance of the river’s ecosystem. This living fossil may not be glamorous, in fact it's quite spooky and ugly, but it’s a vital and fascinating part of Iowa’s natural history.