- Author Existence Failure: The first artist for the Caterpillar spinoff, Isuka Hakozaki, died in April 2013. This led to the manga being put on hiatus until Hayami Tokisada took over in January 2014.
- No Export for You: Arachnid is only available in a few asian countries. It got published in France by Soleil.
- What Could Have Been:
- In the first Arachnid pilot available on the author's website there is no Yoriko, Suzumebachi isn't bald and the aftermath of Alice's battle against Kumo is different. There is also a notable lack of insect biology lectures.
- The second set of sketches is close to the final version, though the last few scenes weren't made available.
- In the Caterpillar pilot, both Imomushi and Hotaruga are men. Paraponera goes after Imomushi after his defeat, but dies standing up while trying to kill him.
- The Wiki Rule: The Arachnid Manga Wiki.