Some people are questioning the authenticity of an online video that appears to show a parasitic worm emerging from the stomach of a praying mantis. But a Canadian entomologist says he's seen the phenomenon many times before.

The video, which was published in the popular blog "IFLSCIENCE!" on Monday, depicts a scene reminiscent of a sci-fi film.

At the start of the two-and-a-half-minute video, a praying mantis is seen crawling across a flat surface before being sprayed with some sort of fluid.

A few seconds later, a thin black worm begins to emerge from the insect. The worm continues to wriggle and squirm its way out of the insect for nearly a full minute, revealing its long slender body (which is much longer than the body of insect itself).

Some of the commenters on the video suggest the worm is a horsehair worm (also known as Nematomorpha or Gordian worm).

The horsehair worm can range in size, with most species measuring between 50 to 100 centimetres in length. However, in some circumstances the worms can grow up to two metres in length.

Adult horsehair worms live freely in the water, but their larvae act as parasites on several different insects.

In 2002, researchers investigated anecdotal reports of insects infected with the parasite "committing suicide" by jumping into water.

The researchers compared the behaviour of crickets infected with the worm against uninfected crickets, and found the infected ones were more likely to jump into the water. Water is fatal for the crickets, but the parasite relies on the water to reproduce.

The authors suggest that once infected, the crickets display "erratic behaviour" which brings them "sooner or later close to a stream and then a behavioural change that makes them enter the water."

While some of viewers have expressed doubts about the authenticity of the video, Prof. Christopher Darling from the University of Toronto said it's a fairly common phenomenon.

"Nothing too strange here," he told CTVNews.ca in an email. "I am pretty sure that this is real, and not a hoax. I have seen and photographed similar things a number of times."

Darling, who is also a senior curator of entomology at the Royal Ontario Museum, said the worm was likely tightly packed inside the abdomen of the insect until the insect died.

"And yes, they do look very long, but they are very skinny!" he wrote.

The video, which was first posted on last May, has garnered more than 720,000 views as of Tuesday afternoon.

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