There is an urban legend stating that the daddy long-legs spider has the most potent venom of any spider, and this same legend is attributed to crane flies where they commonly go by the name "daddy-long legs" (principally in the United Kingdom).
However, both the daddy long-legs spider and the crane fly are in fact innocuous; the spider's venom is practically harmless to humans, and the crane fly is not venomous. The commonly confused harvestman, also known as daddy long-legs but which isn't a spider, is also not venomous.