The question requires understanding which animal is known for producing silk. Let us evaluate each option:

1. Musca domestica: Commonly known as the housefly, it is not involved in silk production. Houseflies are primarily considered pests and do not have any biological relation to silk.
2. Bombyx mori: This is the scientific name for the silkworm, which is the larva of the silk moth. Bombyx mori is renowned for producing silk fibers in its cocoon stage. This option is the correct answer, as silk is harvested from the cocoons spun by these larvae.
3. Butterfly: While butterflies do undergo similar stages of development as moths, they are not used in silk production. Silk is specifically associated with the Bombyx mori moth larvae, not butterflies.
4. Culex: This refers to a genus of mosquitoes, not linked to silk production. Culex mosquitoes are typically associated with spreading diseases such as West Nile virus and are not silk producers.

Based on the options provided and the biological knowledge of silk production, the correct answer is Bombyx mori.

Thus, \(Bombyx \ mori \, (Silkworm)\) is the organism from which silk is obtained.