Pill bugs, also known as roly-polys, are not insects but rather crustaceans. They breathe through gills and are more closely related to shrimp and lobsters than other bugs. – WTF Fun Facts
Source: https://www.scientificamerican.com/article/springtime-science-whats-home-sweet-home-to-a-bug/
Arachnids, crustaceans, and insects do not contain blood but hemolymph instead. In the case of insects, hemolymph does not play an important role in oxygen transport. Some common uses are: creating a hydraulic system, autohemorrhaging, and gluing themselves to other animals. – WTF Fun Facts
Source: https://www.scientificamerican.com/article/how-is-bug-blood-differen/
At night, Parrotfish protect themselves from tiny blood-sucking crustaceans called gnathiid isopods by creating a mucus cocoon which they sleep in. – WTF Fun Facts
Source: https://royalsocietypublishing.org/doi/10.1098/rsbl.2010.0916