domesticated silkworm
Refers to silkworms (Bombyx mori) raised for silk production, as opposed to wild silkworms (野蚕).
See also: 野蚕
Domesticated silkworms are raised for silk production.
From 家 (domestic) + 蚕 (silkworm). The reading かさん is the on'yomi of the kanji.