Martian Insect

Martian Insects were small non-sapient insectoid creatures that once inhabited planet Mars, but are long extinct by now. Images of their fossils have been displayed in the USS Enterprise-D's computer on some occasions.

Behind the scenes
According to the "Spaceflight Chronology" reference book, these creatures are three centimeters long and are silicon-based lifeforms. Their fossils date back to several millions of years ago and were first discovered in 2021. This actually contradicts canon information, as the Horta, discovered in 2267, were clearly stated to be the first silicon-based lifeforms ever recognized by science. One in-universe explanation would be that the fossils were simply believed to be silicon-based in nature, but there was no consensus about this until the discovery of a living silicon lifeform, namely the Horta.