Firefly squid

This is a beautiful little animal with a brief and brilliant life.


Watasenia scintillans is a small (mantle length,~6 cm; wet weight,~9 g), luminescent deep-sea squid, indigenous to northern Japan. Females carrying fertilized eggs come inshore each spring by the hundreds of millions, even a billion, to lay eggs in Toyama Bay (max. depth, 1200 m) and die, thereupon completing a 1-year life cycle.

Watasenia possesses numerous (~800), minute dermal light organs (photophores) on its ventral side. Other organs are scattered over the head, funnel, mantle, and arms, but none is found on its dorsal side. There are five prominent organs beneath the lower margin of each eye. They all emit a bluish light. A cluster of three tiny black-colored organs (<l mm diam) is located at the tip of each of the fourth pair of arms. They emit brilliant flashes of light which are clearly visible to the unaided eye even in a lighted room. Some of the flashes have a cadence resembling that of a terrestrial firefly flashing at night, and thus the squid is known in Japan as the “firefly squid” or “hotaru-ika.”

A billion die every year as a natural part of their lifecycle; all those glittering little creatures dying profligately—Nature is both exuberant and pitiless, it seems.

Tsuji FI (2005) Role of molecular oxygen in the bioluminescence of the firefly squid, Watasenia scintillans. Biochem Biophys Res Commun. 338(1):250-253.


  1. SEF says

    Ah, it seems I have to use FireFox (or at least not IE) for some unexplained reason. Perhaps a FAQ would help with that sort of thing (also no email, URL, login, keyword etc required now) and the new layout will take some getting used to … except I probably won’t be coming past often anyway if I have to load up FF to see the pretty pictures. :-/ It isn’t much of a science blog without pictures (whether of critters, phylogenies, graphs, galaxies etc).

  2. says

    I used to live in Toyama and I never went to see the firefly squid. Actually a friend told me that the aquarium where they were displayed practiced cruelty to squid. Apparently they are rather delicate and many die as they are cruelly forced to to emit light for the sadistic delight of tourists. She told me this over a plate of octopus balls.

  3. Stephanie says

    SEF: I can see the picture (and such a pretty squiddie it is!) just fine in IE. Perhaps it’s your computer?

  4. SEF says

    Well it’s certainly not simplistically my computer because I can see the images with FireFox. So ZoneAlarm or display settings would have to be interfering rather selectively!

  5. says

    As I understand it, the faint lighting on the underside of marine organisms camoflauges them from below at night because they blend in with whatever surface light there is. Thus it’s an evolutionary advantage both for hunters and prey.