In the Ulster Cycle of Irish mythology, Dubthach Dóeltenga ("beetle-tongue", beetles being proverbially black) was a cynical ally of Fergus mac Róich who rarely had a good word to say about anyone. He accompanied Fergus to escort Dierde and Naoise back to Ireland under the orders of Conchobar and later followed Fergus into exile in Connacht following Naoise's murder under Conchobar's orders. He was responsible for the death of Conchobar's son, among others. He later fought beside him in the Táin Bó Cuailnge, although at one point Fergus kicked him right out of the camp for his plans to kill Cú Chulainn.
- MacKillop, James. "Dubthach Dóeltenga". A Dictionary of Celtic Mythology. Oxford University Press. Retrieved 30 April 2013.
- Anon. Táin Bó Cúalnge. The Scythed Chariot. Retrieved 30 April 2013.
Fergus mac Fóig heard this, and it grieved him that Dubthach should advise the hosts to betray Cú Chulainn. And he gave Dubthach a strong and violent kick so that he fell on his face outside the group.