SUMMER 2019 The Summer of Torah, Hesed, and Charity

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WHY DO CRABS HAVE EYES ON STALKS?

By: Efraim Harari



Crabs live in muddy and murky environments where visibility is poor, so they were created with very sharp eyesight to be able to spot predators from all directions and to locate their prey.

One of the distinguishing features of the crab is their eyestalks; their eyes are on stalks (thin supporting structures on their bodies). These eyestalks help the crab see while hiding under water, mud, rocks, or sand. The eyestalk is a long protrusion that extends the eye away from the crab’s body, giving the eye a better field of vision. Eyestalks can move in different directions and allow the crab to monitor
their surroundings.

The crab’s eyes can move and function independently of each other on their individual stalks. Crabs are also able to extend or draw in their eyestalks at will. For example, if a crab feels threatened, it will fold down its eyestalks into grooves in its carapace (protective shell), allowing the creature to scramble away into a hiding place without damaging the eyestalks.

Super Crab 

The largest crab is the Japanese spider crab. Its leg span can reach up to thirteen feet from claw to claw!

How Crabs Can See So Well

The eyes on the stalks of the crab are called compound eyes. These are made up of many individual mini-eyes, called ommatidia(ommatidiumin singular). Depending on the species, a crab can have over 8,000 of these ommatidia. These allow the crab to look in multiple directions at any time, including overhead and behind them.

However, unlike people’s eyes, the crab’s eyes do not move. Each ommatidium can only see in one direction. The images of what each one sees are transmitted to the crab’s brain, where the complete picture becomes assembled. This enables the crab to see in all directions at the same time.

It was only recently discovered that the compound eyes of the crab also help them detect UV (ultraviolet) light under water. Studies have shown that crabs are able to detect UV light for over half a mile below the surface of the ocean. This ability allows the crab to recognize the bioluminescent
(glow-in-the-dark) colors of plankton and other prey that make up its diet. The ability works as a protective mechanism for the crab, as well, as it helps the creature detect harmful predators such as anemones.

Torah Connection

When the Meraglimreturned from spying out Eretz Yisrael, they gave a frightening description of the land. The Jews accepted the lashon hara, and were punished by having to wander in the desert for forty years.

Most of the journey of the Meraglimoccurred during the month of Tammuz. What is the connection between Tammuz and
the Meraglim?

Each month of the year corresponds to one of the twelve shevatim. Tammuz corresponds to Shevet Reuven, whose name comes from the word re’eh, which means to see. This hints to the fact that Tammuz is connected to the power of sight.

How do we understand this connection?

Every month has a mazal, a specific sign in the constellation. Sartan, the crab, is the mazalfor the month of Tammuz.
Crabs have compound eyes consisting of several thousand optical units, which enable them to perceive reality through thousands of different channels. Reality is fragmented into thousands of individual pictures. As such, the crab’s eyes are a symbol of our ability to view reality in many different ways, including according to the bias of the viewer.

The crab’s eyes are on stalks that can be lowered for protection into slots on its shell. In other words, the crab can draw back its power of sight. It can withdraw from the world of what exists and confine its sight to a dark interior world, where it sees only itself locked in blackness.

This is what the Meraglimdid, in the month of Tammuz. They projected their own fears about how life would change when the Jews would enter Eretz Yisrael, onto the reality that they saw, and in this way turned all of the beauty of the land into a nightmare of their own invention.