I too agree with the Ortho Home defense. That is the best stuff. We rarely have a spider in the house since usning this stuff. The bottle says it can be used for silverfish too.
I found this about silverfish, no wonder I have seen them around the bathroom: Diet
The favorite food of silverfish is any matter that contains starch or polysaccharides, such as dextrin in adhesives. These include glue, book bindings, paper, photos, sugar, hair, and dandruff. Silverfish can also cause damage to books, tapestries, and textiles. Silverfish will commonly graze in and around showers, baths, and sinks on the cellulose present in many shampoos, shaving foams and so on. Apart from these cases, the damage caused by silverfish is negligible and they have no direct effect on human health beyond psychological distress to those who are frightened or disgusted by their appearance. Other substances that may be eaten include cotton, linen, silk and synthetic fibers, and dead insects or even its own exuvia (moulted exoskeleton). During famine, a silverfish may even attack leatherware and synthetic fabrics. In extreme cases, silverfish may live for a year without eating.[2] Silverfish can be found anywhere in homes including, but not limited to, garages, closets, underneath beds, couches, electrical appliances such as keyboards and generally preferring dark areas.