Giant Snails

Ah Florida…sultry weather, orange groves, glistening beaches, pouting beauties, and palm trees…but also walking catfish, killer snakes, and now giant mollusks!  The semi-tropical peninsula is prey to wave after wave of exotic animal invaders.  The most-recent problem creatures are giant African snails, immense land snails that can grow up to 20 centimeters (8 inches) long. There are three extremely similar species of giant snails which come from West Africa: the giant African snail (Achatina fulica), the giant Ghana tiger snail (Achatina achatina), and the margies (Archachatina marginata).  Each snail has a brown swirly shell and grows to be about the size of an adult’s fist.

Archachatina marginata

The giant snails eat over 500 varieties of plants—including the majority of agricultural and ornamental species.  They also have a taste for stucco and siding so some Floridians now awaken to discover that huge mollusks are literally devouring their houses.  The snails are hermaphrodites and can lay up to 12000 eggs per year.  They can survive freezing temperatures.

Authorities continue to investigate how the snails got into the country but increasingly the evidence points to…voodoo.

In the Yoruba creation myth, the entire world was once water.  The god Obatala possessed a magic snail shell which contained earth. Acting on instructions from the supreme divinity Olódùmarè, Obatala cast this land upon the oceans, thus creating the continents.  Obatala then molded the land into men and beasts–but he possessed an artist’s temperament and thirst. As he crafted the Earth and its inhabitants he drank so much palm wine that his mental clarity became dulled and he made big parts of existence wrong.  Eventually he passed out altogether and his brother Oduduwa was left to finish the work and patch up the errors as best as he could.  Unfortunately big parts of humanity were assembled incorrectly and these flaws remain in evidence everywhere…

Obatala

Anyway a mainstay of Obatala worship is the sacrifice of snails (in memory of the primordial snail shell which contained the first earth).  Apparently one of Obatala’s worshippers illegally brought some giant African snails into Florida for religious reasons and they escaped from him.

So, to recap, a smuggler who worships a drunken deity brought giant hermaphrodite snails in to Florida as a religious devotion to his addled god.  Unfortunately the snails escaped and they are now eating people’s homes. Argh! What is wrong with us?  I’m going to go drink some palm wine…

Next time please just light a votive candle!

The Giant Clam

A Giant Clam, Tridacna gigas (Photo by Stig Thormodsrud)

Today we celebrate the world’s largest bivalve mollusk, the magnificent and world-famous giant clam (Tridacna gigas).  Native to shallow coral reefs of the South Pacific and Indian oceans, giant clams can weigh up to 500 lbs and measure 50 inches across.  Huge specimens can be very ancient and some have lived for more than a century. Giant clams are hermaphrodites: every individual possesses both male and female sex organs–however a clam is incapable of mating with itself.   They are broadcast spawners producing vast numbers of gametes which they release in response to certain chemical transmitter substances. During these spawning events (which usually occur in conjunction with certain lunar phases) a single clam can release over 500 million eggs in one evening.  Giant clam larvae then swim free among the plankton.  They pass through several mobile transition phases before settling down in one favorite home (as can be seen in the comprehensive life cycle drawing below).

Giant Clam Life Cycle (After H.P. Calumpong, ed. 1992 "The Giant Clam: an Ocean Culture Manual")

As usual for sea creatures, the giant clam has a troubled relation with humankind.  Fabulists have asserted that the great bivalves chomp down on divers for food or out of spite (the clams do slowly shut when harassed, but the movement is a defense mechanism and happens gradually).  They are considered delicacies on many South Pacific islands and naturally the insatiable Japanese pay a premium to eat them as “Himejako”.  Their shells also command a premium from collectors.  Across the South Pacific, giant clams are dwindling away thanks to overfishing, reef destruction, and environmental factors.

Divers with a Giant Clam: Bikini Atoll in the Marshall Islands

It is sad that the gentle and lovely giant clam is suffering such a fate (although aquaculture is now bringing a measure of stability to some populations).  In addition to being beautiful and useful to ecosystems, they are remarkable symbiotic creatures.  A unique species of algae flourishes in the mantle of the giant clam and the clam gains much of its energy and sustenance from these photosynthetic partners. The clam possesses iridophores (light sensitive circles) on its flesh which allow it to gauge whether its symbiotic algae is getting enough sunlight–and perhaps watch for predators.  It can then alter the transparency of its mantle flesh accordingly. According to J. H. Norton, giant clams have a special circulatory system to keep their symbionts alive and happy. The happy and beneficial relationship between a clam and its algae allows the former to attain great size and the latter to remain alive in the ever-more competitive oceans.  I have concentrated on writing about T. Gigas, but there are many other members of the Tridacninae subfamily which lead similar lives (although they do not attain the same great size).  To my eye they are all remarkable for their loveliness.

Tridacna Maxima (in a home aquarium)

Tridacna Derasa (in a home aquarium)