Fromhere:
Since one acre = 4,046 square meters, this gives us a range of 2,589 to 3,406,732 spiders per acre, with a mean of 529,216. So on average, only a half million spiders per acre (but up to three million in some cases).
However, up to 107 million spiders have been found in 4 acres.
Crane fly, although I didn’t really have a word for it until I was an adult. Some people call them mosquito/skeeter eaters, though they don’t eat them.
Daddy long legs if it’s the spider, although I have trouble telling whether it’s 2 or 3 from the image.
3 that you didn’t mention) the non-spider arachnid is a harvestman.
SF Bay Area, California.
Wikipedia lists organisms in four different taxonomic orders that are widely called Daddy Longlegs in popular nomenclature of English-speaking peoples:
Opiliones, an order of arachnids also commonly known as harvestmen
Pholcidae, a family of spiders also commonly known as cellar spiders
Crane fly, a member of the family of insects in the order Diptera
Stylidium divaricatum, a plant in the genus Stylidium
Just as a “snowman” can have a carrot nose or a big foot, they’re both called snowmen.
Growing up in NZ, the only Daddy Long-Legs I knew was the one Colibri lists as a Harvestman. As I started to realise other countries give the name to completely different creatures, a lot of confusion started to clear up.
I am not sure if New Zealand has the spider listed in the OP, though I think they’re what I see a lot of here in Australia. The crane fly I had no name for, it was just another kind of fly, though rare where I lived.
Cranefly or daddy-long-legs.
Harvestman (which I know may not be correct for all long-legged arachnids) or daddy-long-legs-spider.
South coast of England. I think most people around these parts will tend to call both of them ‘daddy-long-legs’ and don’t really care that they are completely different animals.
A Crane fly (though when I first saw one I thought it was the great grandaddy of all mosquitos)
B Daddy longlegs (but we sometimes got into arguments as kids as to whether or not these “harvestmen” were daddy or grandaddy long legs, and we occasionally saw one who qualified for the status of great-grandaddy longlegs.)
The mosquito hawk I like to call a gollywomper.
A) Daddy-long-legs
B) Harvestman
UK, north-east in origin
A. Crane Fly
B. Daddy Long Legs
Toronto, Ont.
a. No specific name I remember- just thought of them as giant mosquitos
b. Daddy-long-legs
A) Uh, I guess I’m just now learning, in my forties, that it isn’t a mosquito
B) Daddy Long Legs
Before looking at the thread:
It’s hard to tell because there’s no context for the size, but I’d call (A) a crane fly and (B) a daddy longlegs. If I’m being careful, I wouldn’t call either a bug and I wouldn’t call (B) a spider, since such creatures are not technically spiders.
[QUOTE=Wikipedia]
Their phylogenetic position within Arachnida is disputed: their closest relatives may be the mites (Acari) or the Novogenuata (the Scorpiones, Pseudoscorpiones and Solifugae).[5] Although superficially similar to and often confused with spiders (order Araneae), Opiliones is a distinct order that is not closely related to spiders within Arachnida. They can be easily distinguished from even long-legged spiders by their fused body regions and single pair of eyes in the middle of their cephalothorax (spiders have an ‘abdomen’ that is separated from the cephalothorax by a constriction, as well as three to four pairs of eyes, usually around the margins of their cephalothorax).
English speakers colloquially refer to species of Opiliones as “daddy longlegs” or “granddaddy longlegs”, but this name is also used for two other unrelated groups of arthropods: the crane flies of the family Tipulidae, and the cellar spiders of Pholcidae, most likely because of their similar appearance.
[/QUOTE]
And I’m pretty sure we’ve discussed this before (the different critters that get called “daddy longlegs”).
Thanks (I think), Colibri; informative and thorough as always. I’ll certainly sleep better knowing it’s only a half million beasties per acre.
I knew there was a reason I left Maryland–that 107 million was just from Phillips Seafood. 
a. mosquito hawk
Though the one in your photo is much more “brawny” than the ones at my house.
b. I get why folks are saying daddy long legs (DDL), but that particular specimen in your photo is what i’d call a “generic” spider. It looks like a DDL, but it spins a (crappy-looking) web.
The DDLs (harvestmen) that I’m familiar with are “grazers” and not “webbers”.
Actually, the bug shown in B is a true spider. Looking at it closely, you can see the division between the cephalothorax (fused head and thorax) and abdomen. As far as I can tell, it does appear to be a pholcid, aka Cellar Spider, some of which are known as Daddy Long Legs. As I mentioned, opiliones or Harvestmen have a single body unit not divided into separate segments.
According to the distribution map on Wikipedia, the DDL’s in my neck of the woods are Cellar Spiders. I’ve never heard that term in my life.
They have two body parts but they’re fused; it’s not like the headmeats share space with the guts.
Trivia-type facts: They are the only arachnids to chew their food (others liquefy and suck), and the only ones to have penises (and only the males, obviously).
Well each male has one. Females can have as many as they want. 
I wish the pictures were clearer/larger.
The first one looks like what I grew up calling a mosquito hawk. Since I have learned that they don’t eat mosquitoes, I’m now using crane fly to describe them.
The second one looks like a harvestman, which I grew up calling daddy long-legs. For me, daddy long-legs is specific to the harvestman critter. The long-legged, web-spinning true spider that some people call daddy long-legs are attic spiders in my lingo. Since harvestman seems less ambiguous, I now use that name.