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This Parasitic Mussel Pretends to Be a Fish

When you think about shellfish, “devious” is probably not the first word that comes to mind. That is, unless you’ve met the parasitic mussel Lampsilis, the trickiest thing on two shells. To attract their hosts, Lampsilis wiggles a fish-shaped lure. When a would-be predator strikes, a pouch inside the lure bursts, releasing a swarm of parasitic larvae into the big fish’s face.

The genus Lampsilis is home to more than 20 species of freshwater mussels, all with a proclivity for fraud. Their delightful common names (Waccamaw fatmucket, lined pocketbook, Alabama lamp naiad) don’t really capture the sophistication of the mussels’ snare.

The scheme starts, as so many do, with sex. During mating season, male mussels spew their sperm into the water column. Because mussels are filter feeders, the sperm-water is sucked in by nearby females. Once their eggs have been fertilized, the females transfer them into a special brood pouch. Soon, the eggs will morph into a special type of parasitic larvae called glochidia. 

Little teeny mussels!

Those itty-bitty shells are not just for show. The larvae are going to need them for what comes next.

Once her larvae have reached the glochidia stage, a female Lampsilis mussel goes into total Decepticon mode. She pushes two flaps of her mantle together to form an extremely convincing fish decoy. Inside that decoy, like a terrifying crunchy center, is the brood pouch full of glochidia.

As soon a potential host approaches, the female mussel starts wiggling her faux fish. And it’s not just any old fish; each Lampsilis lure is customized to imitate the prey of nearby host fish. Unlike real prey, the decoy doesn’t swim away, which makes it especially irresistible. It’s just sitting there!

So the big fish bites, and then things get kind of gross. The bite punctures the brood pouch and releases a cloud of glochidia.

The little larvae make their way into the fish’s gills, where they clamp on with their tiny shells. Then they dig in and start growing.

The host fish’s body is understandably not okay with this. Its immune system fights back, enclosing each larva in a cyst. But like tiny honey badgers, the larvae don’t care.

They’ll ride the big fish train until they morph into the next growth phase. Sometimes that’s 10 days, and sometimes it takes months. When the time is right, the mini shellfish pop out of their flesh prisons and sink onto the riverbed, where they’ll live out the rest of their lives. In most cases, the host fish simply swims away, suspiciously lighter than it was a few minutes ago. 

Why do this? Two reasons: defense and dispersal. Once it gets past its host’s immune system, a baby mussel buried in the gills of a bass is pretty safe. And unlike their parents, Lampsilis larvae are cruising. The bass bus will take them to places their parents have only dreamed of.

For simple animals, Lampsilis mussels rely on a pretty complicated scheme. Fortunately for them, it works; unfortunately, fish fraud may not be enough to save them. “Freshwater mussels are the most, or among the most, imperiled group of freshwater organisms in North America, and some cases you could argue in the world,” Lampsilis expert Bernard Sietman told WIRED.

To preserve the mussels’ majestic weirdness, fish and wildlife agencies have begun rearing mussel larvae in laboratories and releasing them into their river habitats. That’s right: Even humans have started to do the mussels’ bidding.

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Watch a School of Humpback Whales 'Fish' Using Nets Made of Bubbles 

Just like humans, humpback whales catch many fish at once by using nets—but instead of being woven from fibers, their nets are made of bubbles.

Unique to humpbacks, the behavior known as bubble-net feeding was recently captured in a dramatic drone video that was created by GoPro and spotted by Smithsonian. The footage features a school of whales swimming off Maskelyne Island in British Columbia, Canada, in pursuit of food. The whales dive down, and a large circle of bubbles forms on the water's surface. Then, the marine mammals burst into the air, like circus animals jumping through a ring, and appear to swallow their meal.

The video offers a phenomenal aerial view of the feeding whales, but it only captures part of the underwater ritual. It begins with the group's leader, who locates schools of fish and krill and homes in on them. Then, it spirals to the water's surface while expelling air from its blowhole. This action creates the bubble ring, which works like a net to contain the prey.

Another whale emits a loud "trumpeting feeding call," which may stun and frighten the fish into forming tighter schools. Then, the rest of the whales herd the fish upwards and burst forth from the water, their mouths open wide to receive the fruits of their labor.

Watch the intricate—and beautiful—feeding process below:

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