Insects and Related Organisms 
No discussion of organisms that damage or destroy trees or forest products is 
complete without reference to some species of mollusks and arthropods other than 
insects. A number of others in the hierarchy of arthropods, such as crustacea, 
millipedes, centipedes, scorpions, spiders, mites, ticks, etc., are commonly en- 
countered in woodland settings, so they are included in this book. Some species of 
mites, in particular, may damage, even destroy trees, while others are beneficial as 
predators of pest insects. 
Phylum Mollusca—Shipworms 
Wood submerged in salt water is attacked by several species of bivalve mollusks, 
commonly known as shipworms. These relatives of clams, mussels, and oysters can 
cause severe damage to pilings, especially along the Gulf Coast and along the 
Atlantic Coast south of the Chesapeake Bay. Boats are also damaged occasionally. 
These organisms are discussed briefly because the damage they cause is similar to 
and often confused with that caused by wood-boring insects. 
The genera 7eredo and Bankia contain the so-called shipworms. Their bodies are 
long and soft. They are armed with small, chisellike shells at the anterior end and 
there are two siphon tubes at the posterior end. They are free-swimmers in the early 
larval stage, and during this period the body is protected by a bivalve shell. Free- 
swimming larvae seek out wood and attach themselves to it near the mud line. Then 
they bore into the wood, leaving very small openings to the outside. Once inside 
they develop rapidly, enlarging and lengthening their tunnels as they grow. During 
this period when the shell is no longer needed for protection, it is used as a boring 
tool. As they develop, shipworms secrete a calcareous material with which they line 
their tunnels. The openings made by the young larvae are never enlarged. As a 
result, the only external signs of infestation of a piece of heavily damaged wood are 
tiny holes in its surface. 
Because a single piling may contain several thousand shipworms, it may be 
literally honeycombed (fig. 8). In such situations, tunnels may be no more than 6 
mm in diameter and only a few centimeters long. Under the most favorable 
conditions, however, the tunnels may reach a diameter of 2.5 cm and a length of 1.2 
m. 
The genus Martesia also contains a number of destructive species. They differ 
from the shipworms in being clamlike. The young are also free-swimmers and seek 
out and attack submerged wood, making small, inconspicuous entrance holes. 
Once inside the wood, they grow until they are approximately 25 mm in diameter 
and 60 mm long. As they grow, they enlarge their cavities to accommodate their 
bodies. Members of this genus are found along the shores of the Gulf of Mexico. 
Damage to pilings by shipworms can be prevented by impregnating the wood 
with a suitable preservative. Coal tar creosote (American Wood-Preservers’ Asso- 
ciation specification) is recommended for treating waterfront timbers of Douglas-fir 
and southern pine. Copper naphthenate 1s usually used for the protection of wood in 
boats. Coatings of paint and metal are also effective as long as they remain intact. 
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