
Fiddler Crabs 
Ecology 
The saltmarsh fiddler crab, Uca nax, is primarily a species of 
muddy soil and saline waters. Itis usaaty found in the zone between high 
and low tide. Within the salt marsh, it occurs commonly on mud banks of 
creeks and ditches, on sandy-mud shores of bays and river mouths, on sods 
of sparse marsh grass, and on moist, bare flats, 
Most male and female fiddlers over } inch in width dig burrows 
which serve as their homes. Males are especially territorial and usually 
confine their activities to the immediate vicinity of their burrow entrances, 
but females and young tend to wander. However, such wanderings are gener 
ally limited to distances less than 15 feet. The burrow serves as a refuge 
during periods of overcast skies or darkness, at high tide, or in times of 
danger. The greatest numbers of crabs are likely to be observed on clear, 
sunny days during ebb tide. 
Methods of Study 
Assessing the damage of DDT sprayings to marsh fiddler crabs was 
complicated by several factors. Some of the difficulties were evident at 
the study's outset but others became more apparent during its progress. 
From the beginning it was clear that population counts would not be easy. 
Droves of feeding fiddlers on mud banks or elsewhere disappeared quickly 
into their burrows when approached. Furthermore, counts attempted from a 
distance omitted many of the smaller individuals. 
Four principal methods were employed in trying to determine harm 
to fiddler crab populations from DJI sprayings. These were: (1) General 
observations; (2) enclosures; (3) closing burrows; and (1) soil-surface 
sampling. 
General Observations 
The first spraying on the 1.6 area was made during high tide. 
This factor probably reduced greatly the extent to which fiddlers came 
into direct contact with DDT spray. Subsequent opportunity for DDT contact 
was further reduced by unfavorable weather; yet on the first and second 
day after spraying there was evidence of some mortality. Recent kills were 
found and there were increased numbers of claws from many others which had 
been eaten by birds. | 
The second spraying caused considerable mortality. Even five days 
after the application many dead fiddlers were found and many in the deeper 
creek channels were dying. 
As in the case of the 1.6 dosage, the 0.8 treatment caused a 
moderate loss, though the evidence of effects appeared somewhat later. 
Both the first and second sprayings resulted in widespread kills. In 
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