They are difficult to eliminate, not because they are resistant to treatments but because they often hide deep within walls or attics where treatments are difficult to apply. Apply a residual pest control dust product into all cracks and voids where activity has been seen. You may need to treat the attic beneath insulation where silverfish are found. Silverfish do not respond well to feeding on insect baits so crack and crevice treatments are the best options. Persistence in inspecting and treating new areas of activity over several months is also helpful. Experience has shown that homes with wood shingle roofs typically have the most difficult of silverfish infestations.