A fly larva discovered among the remains of an Italian Renaissance princess -- often credited to be the true Mona Lisa -- has a produced a zoological puzzle, raising questions about the origins of the insect.

Widely believed to be a native of the Americas, the black soldier fly (Hermetia illucens) thrives on decaying organic material. It was thought to have first reached Europe in the early 1900s.

“We can now prove the insect was present in Europe several centuries before,” Gino Fornaciari, professor of history of medicine and professor of paleopathology and funerary archaeology at the University of Pisa, told Discovery News.

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“Indeed we found a larva in the sarcophagus of the Italian princess Isabella of Aragon, who died in 1524,” he added.

Isabella, the daughter of King Alfonso II of Naples, married her first cousin, the Duke of Milan Gian Galeazzo Sforza, in 1489.

For the occasion, Leonardo Da Vinci, who had been working in Milan as the court artist since 1482, orchestrated a magnificent party with plays, robots and fountains. Some art historians now argue that Isabella, and not Lisa Gherardini Del Giocondo, was the sitter for the Mona Lisa.

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Her husband was never able to rule, because his uncle, Ludovico, confined Gian Galeazzo and Isabella in a castle-prison in Pavia. Isabella, who complained that her marriage was historically bad, remained there until her husband died suddenly at 25, possibly poisoned by Ludovico.

She then returned to Naples and finally died there at the age of 54, likely poisoned by her own medicine to treat syphilis.

According to Fornaciari, who exhumed her body, Isabella’s teeth were covered by a black patina which was intensively and intentionally abraded.

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The black color was produced by mercury, the drug she was given in massive doses to treat -- ineffectively -- her syphilis.

Among her remains, near the skull, the researcher found two body parts belonging to a fly larva, which was identified as a black soldier fly.

Often confused with a wasp, this insect is well known in forensic entomology as it dominates decaying bodies.

“It is highly unlikely the black soldier fly reached Isabella’s body centuries after her death,” wrote Fornaciari, along with Giovanni Benelli, an entomologist at Pisa University, and colleagues in the Journal of Archaeological Sciences.

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The sarcophagus was previously opened by thieves when the body was already skeletonized, making it unsuitable for the black soldier fly.

The finding raises new questions about the origin of this insect. According to the researchers, there are three possible scenarios.

One theory questions the American origin of the fly and suggests it was a native of the Paleartic region -- stretching from western Europe to the Bering Strait -- even if the insect remained unknown until 1926. The other hypothesis suggests the larva does not belong to the Hermetia illucens but to a new, closely related species or to a cryptic one.

According to Fornaciari, a third scenario is the more likely. The fly might have travelled -- concealed in rat cadavers or decaying food — from the Americas to Europe aboard the Spanish galleons visiting the port of Naples.

Photo: At left, a marble bust portrays Isabella of Aragon by Francesco Laurana (1490) in the Kunsthistorisches Museum in Vienna. Credit: Vassil/Wikimedia Commons. At right, a black soldier fly -- adult and larva. Credit: Gino Fornaciari