Community Magazine August 2019

AV - ELUL 5779 AUGUST 2019 89 How Crabs Can See So Well Efraim Harari Connection 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 Meraglim did, 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. Available Online and at All Judaica Stores! The Latest Book by The Jewish World of Wonders Fascinating Questions & Answers on the Mysteries of the Animal Kingdom Can be ordered online at: www.israelbookshoppublications.com and Amazon. The eyes on the stalks of the crab are called compound eyes . These are made up of many individual mini-eyes, called ommatidia ( ommatidium in 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.