Nursery web spiders can appear to be pretty horrifying if you don't like spiders. They're quick, agile, and can even walk on and dive under calm water. And they're big. 

Fortunately, they're of little threat to humans and will not bite unless provoked and aggravated.  They get their name from the female's behavior of carrying her egg mass in her jaw and building a web tent in which the eggs can hatch. She evens stays around until the last spiderling has hatched. How sweet!