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SYFY WIRE Science Behind the Fiction

Science Behind the Fiction: Mothra's silk could circle the globe 324,000 times

By Cassidy Ward
Rebirth of Mothra III

Over the past 65 years, the Godzilla franchise has introduced the world to a slew of beloved kaiju. Perhaps none of these monsters are more lovable that Mothra, the protector of humanity. Mothra was conceived of in the 1961 novel The Luminous Fairies and Mothra and made her first on-screen appearance three years later in the film Mothra vs. Godzilla. Now, she is making her first appearance in an American Godzilla movie, Godzilla: King of the Monsters, it's time to discuss what makes Mothra so special.

While Mothra has been known to wreak havoc and destruction on persons and property, it has always been in pursuit of good, either defending from other monsters or protecting her own. She hails from Infant Island where she lives as a goddess to the indigenous people. Caught in a cycle of immortality, she repeats the cycle from egg to chrysalis to full-blown moth-monster. But what might that mean for her and for us?


We know that, unlike some of the other kaiju of Godzilla canon who were born of radioactivity, Mothra exists in her natural state, completing the full process from egg to adult before being reborn. While Mothra is an immortal entity, existing from one iteration to the next like the mythical phoenix, she still reproduces in a recognizable way.

While asexual cloning of oneself is not a method of reproduction we are familiar with, it does exist in nature. Parthenogenesis occurs when macroscopic animals fail to find a suitable mate and spontaneously reproduce. This process does occur in some insects, including certain variants of moths.

Mothra, during the course of her more exciting endeavors, plants eggs to ensure the survival of herself and her species. Because the sample size of Mothra-like individuals is so small, we must examine more common species to glean any information about the life-cycle of this incredible being.

Typically, moths and butterflies deposit their eggs on plants which will serve as a food source in their offsprings' early life; once the eggs hatch, they'll need a lot of food in order to progress to the next stage.

Mothra differs from many moth species in that she exhibits behavior independent of mating. In some moth species, females exist only to reproduce, seeking out a mate immediately after emerging from the cocoon. Depending on the species, they'll lay a significant number of eggs, ranging from 40 to 1,000. Mothra is independent in this regard, laying very few eggs, which might explain her more active role in defending not just her own life but the life of her progeny.

Time spent in the egg stage can range from a few days to several months, depending on the species and the environment. Given the fraught nature of existence for Mothra and her offspring, it's reasonable to assume the egg stage would be relatively short-lived, leading to early hatching and…


Once an individual reaches this stage, its primary function is to eat and grow. It eats, sheds, grows, and continues this cycle until it is ready to pupate. Many caterpillars only eat a specific type of vegetation, which we would have to assume is present for Mothra's young on Infant Island.

The Monarch caterpillar eats 200 times its body weight in milkweed before developing a cocoon, which gives us some clue to the amount of food a Mothra caterpillar might need to metamorphose.

The larval stage of Mothra is estimated to weigh between 10,000 and 15,000 tons, meaning it would need to consume 2 to 3 million tons of vegetation before it was ready to move on to the next stage of its life.

This might seem like a lot of plant matter, and surely it is, but Mothra would do well in an environment like the Amazon rainforest, where more than a billion acres exist and every 2.5 acres holds roughly 900 tons of plant matter.

Even when considering that it might have a preference for a specific type of vegetation, Mothra's spawn would likely find all the food-stuffs they'd need to mature in such an environment. Though it is lucky there are never more than a few at a time, as an island environment could not support a large Mothra baby population.


There are some misconceptions as to what occurs at this point regarding butterflies and moths. Butterflies, the more conventionally attractive of the group, typically harden their exteriors and create a chrysalis, whereas moths spin silk to create a cocoon.

A silkworm produces roughly two grams of silk from its cocoon. The Mothra caterpillar, however, could produce thousands of tons, enough silk to reasonably satisfy the fashion industry for the foreseeable future.

The average silkworm cocoon weighs between 1.5 and 2.2 grams; from that, about a third of a gram of silk can be obtained. The Mothra larva weights almost 10 billion times an average silkworm. So if silk production is consistent, a single Mothra would produce more than 3,000 pounds of silk over the course of a few days.

It's also worth noting that silkworms spin one continuous strand of silk, which can be up to 1,300 meters in length. If unspooled, Mothra's strand of silk would be long enough to wrap around the Earth 324,000 times.


Finally, Mothra would emerge as an adult, freed from her cocoon and capable of not only protecting humanity but feasting on the nectar of tens of thousands of plants. No longer would we have to concern ourselves with the colony collapse of bees. Mothra and her children would be capable of handling everything on our behalf.

In a world which consists of various incredible monsters like Godzilla, Rodan, and Ghidorah, we should be grateful for a defender like Mothra who, after everything she must endure simply to exist, is willing to defend us against immeasurable foes.

Godzilla: King of the Monsters hits theaters this weekend.