Myths

(I'll add pictures later)

According to popular culture, daddy-longlegs are viscous spiders whose fangs are too small to bite you, but whose venom is so potent it would kill you if it could.

In reality, there are four different species commonly referred to as "daddy-longlegs."

In the United States, Americans use the term in reference to an arachnid called a harvestman. The harvestmen lives underground, and--more importantly--is not a spider, and therefore has no venom. Fangs, yes. Venom, no.

In Brittain, Canada, and some parts of South America, a daddy-longlegs is a type of cranefly, which is an insect.

And then there is the house spider, daddy-longlegs, whose venom has been proven as among the least potent of all spiders.

Lastly, there is also a plant nicknamed "daddy-longlegs," called Stylidium divaricatum. 

So, there are four daddy-longlegs. One is a spider, one is an arachnid, one is an insect, and one is a plant. None of these can kill you.