"A dock spider"

Don’t look at this video if you have any fear of spiders. Dock spiders eat small fish and tadpoles, as well as insects. They move with lightning speed, and can illicit the expletive "Holy sh**!" from the bravest and strongest of men. There are people who have summered on lakes all their lives and have never seen one, because these monsters are skittish, unless they're protecting a nest. More correctly known as fishing spiders, the adults can be about the size of a splayed hand! And yes, they like to live in and around and under docks, hence their name.