The Mosquito Hawk
You've seen them, those big, gangly, ridiculously long-legged bugs that look like mosquitoes on stilts. What little anecdotal information I gathered on them at Boy Scout camp led me to believe that they are hunters of mosquitoes, but this turns out not to be the case.
What we are seeing (and occassionally ducking out of the flightpath of) is a crane fly. (see bio at bugbios.com) The common crane fly around here is of the family Tipulidae. The adult flies live for only a day or two - long enough to mate, but not long enough to eat. Hopefully they ate enough while they where larvae to keep up their stamina. The larvae are fat gray-brown beasts that roam around in decaying organic matter, like in the top few inches of your yard. They are a favorite snack of songbirds.
In England, these flies are known as "Daddy Long-Legs," which are not the spindly spiders which we have here, and which are also known as mosquito hunters. While they might eat a mosquito now and then, they apparently prefer other spiders, which they kill with their venom.
It has been said that Daddy Long-Legs are the most venomous spiders on earth and that we people are lucky that their mouths are too small to bite us. There is some truth to that rumor. They are venomous and their mouths are too small to bite a person, but there is no evidence that their venom is any more or less poisonous than is needed to kill the small insects and spiders it eats.
Oh, and technically, the Daddy Long-Legs, while an arachnid, is not a spider because it has a penis. (Hence, I guess, the name "Daddy")