COMMUNITY MAGAZINE March 2021

72 COMMUNITY MAGAZINE Exploring the Mysteries of the Animal Kingdom Torah The fly is mentioned often in the Gemara, and is usually characterized as being annoying. For example, the Gemara ( Shabbat 77b) explains that the reason why the ox’s tail is long is so that, while grazing in the meadow, it can beat off flies with its tail. Curtains were hung over beds as a protection against flies ( Sukkah 26a). Also, flies were considered such a nuisance that prayers were ordained for their removal ( Ta’anit 14a). But, as we know, everything that Hashem created has a purpose, even a pesky fly. We find the fly indirectly involved in a couple of monumental events in Jewish history. Parshat Vayeishev (40:1–23) relates the story of how Yosef was sentenced to jail in Mitzrayim, and how he was eventually freed from there. Both the baker and the butler of Pharaoh had sinned against the king. Rashi quotes a midrash that the butler’s sin was that he had served Pharaoh a goblet of wine in which a fly had been found. For this lapse of duty, the butler had been thrown into jail, where he met Yosef, who interpreted his dream for him. When the butler was released from prison, and Pharaoh had some strange dreams, the butler told the king about Yosef the dream interpreter. Pharaoh immediately freed Yosef from jail so that Yosef could interpret his dreams for him. One of the secrets behind the fly’s impressive evasiveness is its outstanding vision. A house fly has two large compound eyes that cover most of its head. Each compound eye is composed of up to six thousand individual visual receptors called ommatidia . Each ommatidium (singular for ommatidia) is a functioning eye in itself, and thousands of them together create a broad field of vision for the fly. Although a fly’s eyes are immobile, their spherical shape and protrusion from the fly’s head give the fly an almost 360-degree view of the world. The thousands of “eyes” allow it to detect even the slightest of movements from nearly every direction. In 2008, scientists used super-slow-motion cameras to learn more about the fly’s remarkable ability of evading predators and fly swatters (see “A Closer Look At” section). It turns out that when a fly spots a predator, or a person waving his arms about, it doesn’t just jump into the air. In the next one-hundred-thousandth of a second, the fly freezes, repositions itself, and perfectly coordinates its legs and wings to lift and fly off in the opposite direction of the incoming threat. Flies do this so quickly that our eyes can’t even follow their pre-flight maneuvering, or predict the path of their escape. It’s a split-second for us — but for the fly it’s enough time for it to save itself. Why Are Flies So Hard to Swat?