Critter Of The Week # 16: Firefly Squid

Image by Dante Fenolio


Known as Hotaruika in Japanese, perhaps no other creature in the ocean puts on quite the dazzling light show as these tiny squid.  They are found throughout the world's oceans but are famous for their dense populations in Japanese waters. As they come up to the surface at night, millions of them glow in large schools and even wash up on shore after breeding. It is one of nature's greatest yet least studied natural wonders of the world.


Scientific Classification

Kingdom : Animalia

Phylum : Mollusca

Class : Cephalapoda

Order : Teuthida

Family : Enoploteuthidae

Genus : Watasenia

Species : Watasenia scintillans


Conservation Status

Firefly squid are classified as a species of Least Concern by the International Union for Conservation of Nature. This means their population has been surveyed and are not in imminent danger of becoming extinct.


Physical Description 

Firefly squid are tiny open water squid measuring only three inches long. They are known as cephalopods, which includes all squid, octopuses, and cuttlefish. They also share a distant ancestor with snails, slugs, and even clams.


The firefly squid has many of the same characteristics of all squid including a soft conical shaped body known as a mantle, large complex eyes, a parrot-like beak for masticating or breaking apart prey, and a fascinating structure called a siphon, which is like a jet propulsion device that sucks in water and shoots it out like a jet-ski, thus propelling the squid rapidly backwards to escape danger. They also have a pair of long feeding tentacles tipped with suckers that they shoot out to capture their meals.


Like all squid, they have large complex eyes and excellent vision. Unlike other species of squid, firefly squid can see in color because of three different pigment cells inside their eyes vs. just one. The theory is this was an adaptation that allows them to differentiate colors from their own glowing cells and the light reflected in the ocean.


What sets the firefly squid apart from other cephalopods is their amazing ability to glow. This process is known as bioluminescence and is made possible by light-producing cells called photophores found all over their body. These cells produce a chemical reaction much like a glow stick, generating the signature soft blue glow. 


How Does Bioluminescence Help Animals Like the Firefly Squid? 



Firefly squid use bioluminescence to communicate with each other, attract mates, capture prey, and even confuse predators.


They confuse predators through two ingenious mechanisms. The first is called counter-illumination and is nature's version of an invisible Harry Potter cloak. 


Counter Illumination

Counter illumination is when the squid produces light that matches an illuminated background, such as the ocean's surface. The squid can control their glow to where they match the background light so well, they are virtually invisible to predators. So if you are a predator from below, looking up at a squid in the moonlit water, they can change their glow to match the water and virtually disappear!



The second method acts more like a warning, or a cry for help, that attracts even bigger predators. When the squid are attacked, they glow, and in the dark depths of the ocean, other large predators see the flash of light and come in to investigate. Oftentimes, they are more interested in attacking the squid's original attacker than the squid themselves. The squid then make their escape as their would-be predator becomes the prey.





What Other Tricks Do They Employ for Camouflage?


Firefly squid have even more tricks up their sleeve to help them keep out of trouble. Like all cephalopods, they have three different types of cells that help them blend in with their environment. 


Firefly squid, and many other squid, have developed an amazing array of tricks to avoid detection.  In this video, you can see just how some of these cells work to give them amazing ways of blending in.



Firefly squid feed on a variety of creatures including small fish, crabs, other crustaceans, and free-floating plankton. Most of these they lure in with their lights and snatch up with their long feeding tentacles that they shoot out rapidly from their bodies. The long tentacles are tipped with suckers that help it grasp the prey and bring it into its mouth.


Their beak then breaks the food into smaller chunks and a rough tongue-like organ called a radula at the back of their throat then grinds it up so it can be easily swallowed.


Behavior & Intelligence

Intelligence has never been measured in firefly squid. But all cephalopods are known as some of the most intelligent invertebrates in the animal kingdom. Their brain-to-body ratio is relatively high, they have complex nervous systems, and are oftentimes social. 

Reproduction & Life Span

The firefly squid spawning season lasts from February to July and is in its highest concentration in Toyoma Bay in Japan. The squid aggregate in such large numbers as a means to overwhelm predators and ensure as many of their offspring survive as possible. 


Females will lay between a few hundred to 20,000 eggs! For such tiny animals, they will lay their eggs in a long gelatinous string up to one meter long (almost four feet). In just two weeks, tiny perfect miniature squid are born.



Once the squid mate and lay eggs, they die and complete their one-year life cycle.


Distribution & Habitat

Firefly squid are found all over the Western Pacific Ocean near deep underwater canyons along the coastlines where nutrients well up from the depths of the ocean and provide them with plentiful food. They live at ocean depths around 200 to 600 meters. At night and during the spawning season, they come up to the surface to feed and reproduce.


The overall population of firefly squid seems to be healthy. It is difficult to estimate the numbers of such a small animal but they are likely in the billions or more and, according to scientists, are not in danger of extinction. 


Relationship with People


Firefly squid are considered a delicacy in Japan, and during the spawning season, the squid are harvested in huge quantities.  The annual catch sizes range from 500 tons to almost 7,000 tons. The average catch each year is 2,000 tons of firefly squid. This represents about 250 million individual squid. So far, the catch seems to be sustainable, but Japanese officials still monitor catches to ensure this natural wonder continues to fascinate future generations.



Japan recognizes the uniqueness of the firefly squid and during the fishing season, tourists come from all over to witness fishermen haul in glowing nets full of firefly squid. A museum has been constructed near Toyoma Bay where the squid congregate and educate people about their behavior and ecology.



If you want to see firefly squid yourself, take a trip to Toyoma Bay in Japan and visit the squid museum, it is truly an amazing spectacle! 


CritterFacts CritterKnowledge Ranking


We rank each new Critter of the Week based on how much information and resources we find online about each animal. We rank on a scale of 1-10. 1 being very little information available or only very basic information available and there is a need for more research. An example would be a newly discovered deep sea creature like the blobfish. A ranking of 10 means there is abundant and easily accessible information available on all aspects of a species. An example would be chimpanzees. We will use this gauge to help us guide future research efforts to learn more about new animals we include in our Critters of the Week!