( The D in this name is pronounced like 'th' in 'thus'. The SH is pronounced like one between 's'in 'sun'and 'sh'in 'shut'. )
(See also the link alarka1. )
Damsha was a demon. He tried to abduct the wife of a sage Bhrigu. Bhrigu cursed him to become an insect named Alarka. Prayed by the demon for relief from the curse, Bhrigu stipulated that his curse will cease when their descendent Raama sees the demon in the insect form.
Once Karna went to Parashuraama at Mahendra hill. He lied to the sage that he was a Braahmana and was learning archery from him. Oneday Parashuraama slept resting his head on Karna's thigh. The insect Alarka bit and bore through Karna's thigh causing a flow of blood. But, Karna did not move at all, fearing disturbance to his teacher's sleep. When the blood flowed and touched Parashuraama, he woke up and learnt what had happened. The insect died immediately after Parashuraama looked at it. It soon assumed the form of a demon. The demon, then, explained about his curse from Raama's ancestor Bhrigu and its relief too.
Parashuraama understood that Karna could not be a Braahmana for bearing with that that great pain and forced Karna to speak out truth. On learning what Karna did, he cursed him that whatever Karna learnt from him would be of no avail at the needed hour while fighting with his archrival in the decisive battle.
Karna returned dejected. Ultimately, Karna was unable to employ the great Brahma-Asthra in his last battle against Arjuna and was killed . Thus, a small insect caused a big turn in the story but there was a good background to it.
DEDICATED TO MY DEAR NIECE VYSHNAVI KRISHNA