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The Strange Lives of Worms: Lunar Cycles and Odd Quirks of Evolution

There are few things in nature that have held the fascination of humans for longer than the Moon has. For longer than humans have been consciously aware of its presence (let alone possessing knowledge as to what the Moon actually is), the lunar influences on Earth biology appear to have played a significant role in the development and behavior of organisms over time.

The various lunar rhythms that many organisms exhibit are well documented in scientific literature and are suggestive of how significantly the moon actually does affect us. From claims of “moon madness” to some who complain of having difficulty sleeping during a full moon, many of the common beliefs associated with lunar effects on human physiology probably do have some degree of basis in fact, despite the fact that modern science recognizes no actual links between strange behavior and a full moon, otherwise known as the “lunar effect”.

“Even partial sleep deprivation over the course of a single night can induce mania, and it is plausible that sleep disturbance during a full moon may function as a positive feedback once a manic episode has begun in a predisposed individual,” wrote coauthors Alina Iosif and Bruce Ballon in a 2005 paper, which looked at whether there might be any reality to claims regarding the lunar effect.

lunar effect

“Perhaps this lies at the origin of the association between madness and the full moon,” the 2005 paper surmised.

While speculations continue about whether any kind of “lunar effect” exists, there are many other examples of lunar influences on organisms that are more easily noticed, though no less strange. For example, a remarkable number of observations have been made over the years showcase the Moon’s ability to subtly govern the behavior of various species of worms, which manifest in several surprising and even bizarre ways.

One of the best examples to date involves the curious lunar-oriented behavior of the palolo worm, a variety of segmented marine worm whose curious breeding behavior is almost legendary in terms of its connections with phases of the moon. Without fail, the breeding season of these curious marine annelids always occurs at the same time of the year during a particular phase of the Moon.


Closeup of the head of a palolo worm (Smithsonian National Museum of Natural History).

During this period, the worms engage in one of the most peculiar mating acts known to exist: the creatures literally sever themselves in half, with their tail portions swimming by the tens of thousands to the surface of the ocean, whereupon they release both eggs and sperm that proliferate the species.

Similar behaviors have been observed in the Platynereis Megalops, whose appearances in “swarms” occur in accordance with lunar phases.

“The swarming occurs nightly throughout the months of July and August during the dark of the moon,” reads what is arguably the “classic” study of the breeding habits of these worms from 1914. “From new moon to full moon, whether there be moonlight or not the animals do not swarm. Only mature animals swarm.”


An example of a male of the Platynereis genus (Wikimedia Commons 4.0).

Of similar intrigue are the breeding habits of the Odontosyllis enopla, a variety of glowing marine worms that persist within the warm and shallow ocean waters off the shores of Bermuda. In addition to their vibrant luminous displays during mating, these unique marine worms also display an uncanny synchronization with lunar phases, appearing at virtually always the same time of night for a period of several days after the full moon of each month. There seems little question based on the clockwork precision of their appearances in accordance with the cycles of the Moon that these creatures use lunar periodicity to their advantage; indeed, scientists who have studied these worms find their lunar-timed broadcast spawning to be a very successful procreation strategy.

A variety of other examples exist, which include oddities so subtle as the direction that various flatworms orient themselves when swimming away from light, which also appears to be influenced by phases of the moon. Perhaps it comes as no surprise then that when the full moon appears in March, it is known as the “Worm Moon,” seemingly in reference to 18th-century explorer Captain Jonathan Carver, who recounted varieties of wormlike beetle larvae that begin to emerge around this time of year.

Indeed, time has shown that many of our world’s most mysterious facets are found in the less often observed areas of nature. Obviously, the peculiar lunar activities of aquatic worms around the world are further evidence of this, and of the mystifying nature of life forms on Earth and their unique relationship to our planet’s natural satellite.


Micah Hanks is a writer, podcaster, and researcher whose interests cover a variety of subjects. His areas of focus include history, science, philosophy, current events, cultural studies, technology, unexplained phenomena, and ways the future of humankind may be influenced by science and innovation in the coming decades. In addition to writing, Micah hosts the Middle Theory and Gralien Report podcasts.
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