Reproductive Consequences: Female Scorpions Experience Reproductive Challenges Due to Constipation, While Males Remain Unaffected.

After the arachnids drop their tails, poop backs up until it kills them, but before that it can affect pregnancy

An Ananteris balzani scorpion couple interlocked in their elaborate mating dance. The male (left) has lost the end of his tail, rendering him unable to defecate.

Faced with a predator, some animals choose to fight. Others flee. A select few fracture themselves into pieces.

Certain scorpions, like many lizards, are capable of breaking off part of their tail during a predatory attack. Unlike lizards, however, these scorpions have a peculiar anatomy in which their anus resides near their stinger at the end of the tail. Thus, when a scorpion breaks off its tail, it comes at a terrible cost. The scorpion loses its ability to defecate, ensuring a slow death by constipation over the ensuing months.

But while a stump-tailed scorpion’s days are numbered, a new study finds that losing the tail apparently imposes few reproductive costs on male scorpions. Females, however, aren’t so lucky.

In the paper, published online in January in American Naturalist, researchers examined the reproductive penalty paid by the scorpion species Ananteris balzani when it loses its tail. These small South American arachnids have a light brown color, delicate pincers and a sting a bit less painful than a bee, according to the paper’s lead author Solimary García-Hernández, who knows from experience. “They’re cute,” she says. “And they are really fast, which is not very common in scorpions.”

Lacking even an established common name, Ananteris has long been little-studied and poorly understood. García-Hernández first began studying Ananteris early in graduate school in 2011, and even found a new species in her parents’ backyard, which she named Ananteris solimariae.

It was a big surprise in 2015 when she, while working as part of a larger research team, found that Ananteris scorpions are capable of shedding their tails. “Autotomy”—the process of dropping a body part to escape a predator—was until then known to have evolved in only a handful of animal lineages like starfish, spiders and certain lizards. But while a lizard that sheds its tail pays a cost—it no longer has the appendage to store fat and locomotion is impacted—the mere act of self-amputation is hardly a death sentence. Not so, for the constipated scorpions of Brazil. Over a period of months, the scorpion’s tiny digestive tract fills with feces, causing the scorpion to become visibly swollen. About eight months after losing its tail, the scorpion dies.

The abdomen of a scorpion that has lost its tail showing the accumulation of feces (white material) in its digestive tract. This scorpion will eventually die of constipation.

“The behavior was so extremely weird that I thought I’d really like to better understand the implications of it,” says García-Hernández. So she designed an experiment to test what costs are imposed on a stump-tailed scorpion over the course of its post-tail life. Of particular interest was how losing the tail affected the scorpion’s reproductive abilities.

To test this, García-Hernández and her team at Universidade de São Paulo first collected nearly 150 scorpions from the Brazilian savanna. Next, she induced about half the scorpions to shed their tail. In the wild, the scorpions might lose their tail in an encounter with a hungry bird or rodent. But in the lab it was up to García-Hernández who tugged at them gently with a small pair of forceps.

The team then set up a series of matings between stump-tailed and intact scorpions. García-Hernández predicted that autotomized male scorpions would be less successful at mating than their fully endowed counterparts, since the tail plays an important role in their complicated mating ritual.

“To start the courtship dance, the males do like a tail-wagging,” García-Hernández explains. “If the female is receptive she lets the male grab her pincers and they start the dance.” During this promenade à deux, both scorpions face one another, pincers interlocked, and tango to and fro across the savanna, occasionally even interlocking mouthparts in a sort of scorpion kiss. The dance can take hours. Eventually, the male deposits a spermatophore on the ground and, using his tail as an anchor, abruptly shoves the female forward over the packet of sperm, which latches onto her genital opening.