These Cute Bobtail Squids are Hiding Just Beneath the Surface of Philippine Oceans

Philippine fauna impresses with large and imposing animals: the largest raptor in the world, the Philippine Eagle, as well as the largest fish and ray, respectively, with the whale shark and the manta ray. But there are also amazing miniature-sized animals in the archipelago. And one of the highlights of this collection of small and very small animals is the bobtail squid.

Keep an eye out for bobtail squids the next time you go diving

Photo by Klaus Stiefel.

What kind of animal is this the bobtail squid? It’s a cephalopod, or an advanced kind of mollusk. Cephalo- means head in classic Greek, and -pod means leg; hence these are animals where the feet (or more precisely, the arms) are directly attached to the head. In contrast to its mollusk cousins—the snails, slugs, and clams—the cephalopods are clever animals with keen senses and fast movements. They have big brains and show complex behavior, such as sneaky hunting techniques, the use of coconut shells as protective armor (which they bring along), and sophisticated camouflage.

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The cephalopods include the octopi, the squid, and the cuttlefish. All of them exclusively live in the ocean. The bobtail squid is most closely related to the cuttlefish, and lives close to the substrate of the ocean, or in shallow tropical and subtropical waters, just like the larger cuttlefish. Cephalopods range in size from the enigmatic deep-sea Giant Squid, which can grow to a length of 12 meters; the Giant Pacific Octopus, with a “wing span” of two meters, to tiny animals on the other end of the spectrum.

Night creatures

One such dwarf cephalopod is the bobtail squid, with a length of five centimeters or less, and one of the smallest cephalopods in existence.

The bobtail squid can usually be found in shallow waters, usually no more than 15 meters deep

Photo by Klaus Stiefel.

To be precise, we should talk about bobtail squids, in the plural. These are a cluster of related minute cephalopod species which look rather similar and lead similar nocturnal lives. In the Philippines we mainly see a species called Euprymna berryi, or Berry’s bobtail squid.

One can find the bobtail squid in shallow waters, usually less than 15 meters deep, generally in the sand. The small squid are most active at night, when they hunt tiny shrimp. It shares the sandy habitats with frogfish, scorpionfish, a variety of marine worms, and sea slugs, which of course are fellow mollusks. The bobtail squid is a part of the “muck diving” fauna which is highly appreciated by scuba divers and underwater photographers.

The bobtail squid likes to burrow itself underneath the sand, with just its eyes sticking out

Photo by Klaus Stiefel.

Many cephalopods have the ability to change skin color in mere seconds. They use this color change to camouflage themselves by taking up the patterns of their environment, or as a way of communicating. A “tiger” pattern, for instance, is a sign of aggression in cuttlefish. The color changes come about by contracting or relaxing tiny circular muscles which are placed around a tiny color patch. If these skin muscles are relaxed, the color patch below them is visible; if they are contracted, the skin color from above can be seen. The bobtail squid uses this system, and you can see the animal go from shades of blue to orange and to a brown skin coloration.

Bioluminescence

An unusual biological “skill” of the bobtail squid is that it can produce light. This is called “bioluminescence.” The light isn’t actually generated in the tissues of the bobtail squid itself but made by bacteria which live in a specialized organ of the animal. The bacteria belong to the genus Vibrio and are therefore relatives of the bacteria that cause cholera in humans.

Be amazed by the bobtail's squid's ability to produce light

Photo by Klaus Stiefel.

But instead of making the bobtail squid gravely sick, they light them up. The bobtail squid has evolved a special light organ where these Vibrio bacteria live. The epithelial cells (related to the intestinal lining cells) of the light organ make sure that only the Vibrio bacteria useful to the squid grow in the light organ, to the exclusion of other bacteria. A biological reflector and a simple lens attached to the light organ allow the squid to precisely manipulate how much light it’s emitting.

The purpose of this system is to camouflage the animal, in a very subtle way. As mentioned above, the bobtail squid roams around on the sand underwater at night; and while the minute’s cephalopod’s surroundings seem dark, there is some moonlight illuminating its environment. This doesn’t allow a predator to make out details in the shape of the squid, but it’s enough light to see that something is there. The light produced by the bobtail squid’s bacteria eliminates the tiny shadow caused by the moonlight.

The bobtail squid, and many other cephalopods, have the ability to change skin color in seconds

Photo by Klaus Stiefel.

Survival in the wild is a game of small margins. As so often, evolution has edged out even the seemingly smallest advantages to ensure survival; in this case a tiny beam of light to eliminate a minute squid’s moonlight shadow.

If this camouflage still fails and the bobtail squid feels that it has been detected by a would-be predator, it digs itself into the sand. This is a curious process: the cephalopod uses its arms to shovel sand onto its body, a few dozen grains at a time. It doesn’t completely disappear under the sand, but typically leaves its eyes sticking out. The little squid’s body is protected, but it can still keep an overview over what’s going on in its vicinity. Admittedly, often it’s my strobe or camera light which has scared the bobtail squid I encountered and made them dig in.

Going on a night dive is the best way to see these fascinating creatures

Photo by Klaus Stiefel.

As a general rule, if you live in or visit the Philippines, you should give scuba diving a try. And as a second general rule, if you scuba dive, you should night dive. Yes, it’s common practice and a great adventure to descend under the waves after sunset. Equipped with a dive light, you can explore the critters that emerge from the hiding places where they spend the day. One of these critters you will see at night is the bobtail squid. Hopefully now, with the knowledge you gained from this story, you can appreciate the sight of this very special small cephalopod’s probing eyes, sticking out from underneath the sand.