noun
pholcid spider; cellar spider
Refers to spiders of the family Pholcidae, especially the common species Pholcus crypticolens. In everyday Japanese, this is the primary meaning.
天井の隅にユウレイグモが巣を作っている。
A cellar spider has built a web in the corner of the ceiling.
noun
Colloquial use for harvestmen (order Opiliones), which are not spiders. Often confused with the spider sense; context usually clarifies.
See also: 座頭虫
ユウレイグモって呼んでるけど、あれは本当のクモじゃないんだよ。
We call it a daddy longlegs, but that's not actually a spider.