Silverfish & Firebrats

There are several different species of silverfish here in San Diego County and two types of firebrat; all of them are small, wingless, carrot shaped insects that have a characteristic metallic sheen that rubs off when you touch them. Silverfish are very reclusive insects with three filaments extending from the tail; they are not often seen by homeowners because they only come out at night and they are very good at getting out of sight quickly when the lights come on. They cannot climb smooth surfaces so it is not that unusual to find one stuck in a tub, sink, or even a glass or bowl in the cupboard.

A silverfish’s favorite food would have a lot of starch such as glue, some types of paper and occasionally linen and silk; they love those cardboard boxes that you have stored in the garage. I find it interesting that most of the homes that have a persistent silverfish problem also have a lot of

unfinished wood surfaces. In fact, you will find more silverfish in the attic and basement than you will in the master bedroom. They have been known to damage clothing, but their main target is old books and pictures. Silverfish mouthparts are ideal for feeding on flat surfaces; they graze over the surface where they feed. Sometimes they will feed on paper, pictures, or fabric without even leaving holes behind them; they just leave the page a little thinner. They prefer humid environments, like bathrooms and sub areas; some researchers claim that silverfish actually feed on mold in moist areas. While they seem to like the exposed wood in attics, I have noticed that silverfish tend to show up downstairs when the Santa Anna winds bring hot dry weather to us here in North County.

Silverfish have what is called a “gradual” or “incomplete” metamorphosis, meaning that they develop into adults by stages rather than by pupation. Nymphs take years to mature into adult silverfish and even as adults they continue to molt and grow for as long as they

live. The primary food source for nymphs during the first few months of their lives is the droppings of adult silverfish; they do not come out into the open during the first two instars of development and this makes them extremely difficult to control with insecticidal sprays and dusts. Another thing that makes silverfish so incredibly difficult to control is that they sometimes spend extended time in a dormant condition; in effect, hiding out without food or water for as much as a year. Silverfish and their warmer cousins, firebrats, are especially long lived for insects. In San Diego County they can live for as much as ten years and they lay between fifty and a hundred eggs during a normal lifespan.