Requiem sharks actually are a family of 12 genera and approximately 50 species. They have a funereal-sounding name, and for spear fishermen, in particular, they can be a lethal menace. That's because fish skewered and struggling on a spear emit low frequency vibrations, which requiems can detect with their highly sophisticated sensory organs. Once they've arrived in the vicinity of the catch and can smell blood, their aggressive instincts can take over. That's not a good thing, if you happen to be in the water with them, because the strong-swimming, torpedo-shaped predators, who travel either solo or in groups, have big mouths filled with sharp, serrated teeth [source: Randall]. Various types of requiem sharks have attacked humans 56 times, with seven unprovoked fatal attacks on record [source: International Shark Attack File].
What makes the sharks even more frightening is that a few of requiem species, such as the grey reef shark, have a distinctive threat posturing. The sharks will swim laterally, toss their heads in an exaggerated fashion, arch their backs with their pectoral fins held downward, and snap their jaws menacingly. If you see a shark doing that, it's best to move slowly away. Requiem species vary in size, but the biggest can exceed 24 feet in length, often making them the biggest bullies on the block [source: Beller].
If there's a silver lining to all this, it's that requiems are voracious eaters who normally dine on a lot of other creatures besides humans, including sharks and rays, squid, octopuses, lobsters, turtles, marine mammals and sea birds [source: Randall]. Large and fierce members of the Requiem family, like the bull shark and the tiger shark, are especially dangerous to humans. We'll get to them in a couple of pages.