Why is 蜀 composed of net (网), packag(ed) (裹) and insect (虫)?
蜀漢領土主要在蜀地，故把它稱為「蜀國」。
蜀地最早是「古蜀國」。
開國之王名為「蠶叢」，他是位養蠶專家。
他為了養蠶事業到成都居住，因而建立了「古蜀國」。
這就是為什麼蜀漢之名會和蠶有關的原因。

The territory of 蜀漢 was mainly in 蜀地, so it was called 蜀國.
The first country in 蜀地 was 古蜀國.
The founder's name was 蠶叢, he was an expert in sericulture.
He moved to Chengdu for his sericulture, and thus established the 古蜀國.
This is why the name of 蜀漢 is related to silkworms.

Source: wikipedia