Silverfish are those antennaed insects you find around your books and bedding. They are named after the silvery glitter given off by the scales that cover their entire body and comprise several species within the order Thysanura. Unlike most insects, these ones lack wings throughout their entire lifespan. They also don't change their morphology or feeding habits when they molt; they just get a little bigger. The general silverfish body plan is very primitive, and probably is older than even that of the cockroaches.
However, like the cockroaches, the Silverfish, and their close relatives, the Firebrats, tend to feed on decaying material, though they also can feed on ink and glue, hence their attraction to books. They can also be found nestling under the bark of eucalyptus trees on campus, under leaf litter and wood chips.
You may ask why they are commonly found in bathtubs or sinks. The answer is quite simple: they have trouble moving on smooth surfaces and are trapped.
Silverfish and Firebrats can become indoor pests, but are generally not as severe as cockroaches or ants. Of course, if you are a booklover, you might think ants are better to have around, as both silverfish and cockroaches eat and destroy books on shelves and in boxes.