This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The historical origin of 蚉 is uncertain. It visually combines 文 and 虫, but the exact development is unclear.
With 文 (writing) over 虫 (insect), you might imagine a tiny insect crawling across a page of text, but its actual meaning is unclear.
For ブン, picture a bun with a tiny insect on it: bun -> ブン, and the insect sits on the bun like 虫 under 文.