Limnoria bore holes about one-sixth inch in diameter and seldom go more than one-half inch below
the wood surface, and may run obliquely for one inch or more. Earlywood is preferred. Wood is
normally heavily infested and may contain 300 to 400 animals per square inch, and the surface of
the wood will be severely honeycombed. The remaining thin wood partitions are broken away by
wave or other mechanical action and new wood is exposed to further attack. The attack is usually
concentrated between half tide and low tide levels, or at mud line where the eroding action is the
greatest. A distinctive hourglass shape (Figure 4-30) results.
The spread of Limnoria is usually slow due to their poor swimming ability. However, water move-
ment and driftwood can serve to spread them.
Limnoria are active along the entire coastal area of the United States. Their activity is accelerated in
warm tropical waters where breeding occurs year around as compared to colder regions.
The method used to prevent Limnoria attack depends on which of the three species are present.
This, in turn, depends somewhat on climatic conditions. L. tripunctate, which is destructive on the
Pacific coast from San Francisco southward, on the Atlantic coast from North Carolina southward,
and on the Gulf coast, is tolerant to creosote in these regions. This species may be extending its
range northward, and it has also been shown that a population explosion can occur if the water
temperature increases slightly. Two preservative treatments are recommended. One is a dual treat-
ment which consists of treating pilings with 1.0 to 1.5 pounds of ammoniacal copper arsenate
(ACA) or copper chrome arsenate (CCA) per cubic foot of wood; drying the wood; and then treat-
ing with 20 pounds of marine-grade creosote or creosote-coal tar per cubic foot of wood. An alter-
native treatment is to use 2.5 pounds of ACA or CCA per cubic foot of wood.
Treatments for the other two species (L. lignorum and L. quadripunctata) found in temperate or
cold waters consists of using 20 to 25 pounds of marine-grade creosote or creosote-coal tar per
cubic foot of wood or 2.5 pounds of ACA or CCA per cubic foot of wood.
18.104.22.168 Sphaeroma. Wood boring species of Sphaeroma (principally
S. terebrans) are found in some, usually brackish, waters along the southeast and gulf coasts and, to
a lesser extent, on the west coast from San Francisco southward. They are most common in Florida
estuaries, but even there, their occurrence is spotty and unpredictable. They seem to be particularly
tolerant of CCA and ACA. Creosote seems to resist attack better but with time becomes susceptible.
The borers are similar to Limnoria, except they are larger and stouter reaching a length of 3/8 to 1/2
inch long and 1/4 inch wide. The burrows are typically 1/4 inch in diameter, generally perpen-
dicular to the timber surface, and usually go to a depth of about three times the diameter (Figure 4-
33). Softer species of wood are preferred. Heavily attacked wood surfaces are often honeycombed.
The wood is used for shelter and probably not ingested.