Members of the order Opiliones are often called harvestmen due to the English folklore that if one was killed, it would lead to a bad harvest. However, another colloquial name is a perfect example of common-name problems. Three different animals are often called "daddy longlegs": the crane fly (superfamily: Tipuloidea) and two species of arachnid, the cellar spiders (Family: Pholcidae) and the Opiliones. While they all have long legs, none are daddy longlegs. The opiliones are not flys. And, while Opiliones are often mistakenly identified as spiders (order: Araneae), there are a few differences. Firstly, they typically only have two eyes (cave and litter species have lost their eyes). Secondly, they lack the venom and silk-producing organs which spiders are known for. Thirdly, their abdomen and cephalothorax are fused (see image, with the abdomen in pink and the cephalothorax in orange), making them look like a pill on the legs. Finally, unlike spiders, they have a penis (I wonder if that's why they are called daddy).