further decreases but in the two lower dosage areas residual effects were 
no longer of importance. It was evident that mortality of insects in tall 
grass growths was only about half of that in short grass. 
Blue Crabs 
Mortality to the blue crabs present at spraying as well as to 
those entering the area with subsequent tides was apparently very heavy or 
nearly complete at the 1.6 dosage application. The 0.8 application caused 
a nearly equal kill. In these two higher dosage areas, toxicity to crabs 
was evident for ten days to two weeks following spraying. Losses were 
lighter under applications of 0.) and 0.2 pounds per acre. However, crabs 
confined to a creek channel in the 0.4 area suffered a 91% mortality. 
kiddler Crabs 
Saltmarsh fiddler crabs, though apparently not as susceptible as 
blue crabs, suffered fairsy heavy mortality from the higher dosages and 
moderate or light kills from the 0.) and 0.2 dosages. The heaviest losses 
were among the small, tick-size individuals. Greater mortality was noted 
in flats than on well drained banks. Mortality occurred for at least ten 
days after spraying at the high dosage levels. 
Other Invertebrates 
Populations of ground-inhabiting and web-building spiders suffered 
greatly from DDT sprayings and showed little sign of recovery by the end 
of the summer. Mites, on the contrary, were generally more numerous after 
spraying and showed the largest gains on the area of highest dosage. Salt- 
marsh amphipods and sowbugs were apparently almost completely eliminated 
at each of the four dosage rates. In contrast to this, the ribbed mussel 
showed little or no effect, and the saltmarsh snail actually increased in 
numbers and size in most study areas after DDT treatment. 
RECOMMENDATIONS 
Since the investigations covered in this report were intended 
to be preliminary to others in the following year or years, a statement of 
recommendations will be reserved until studies are completed and until 
there has been final interpretation of all findings. 
Interior--Duplicating Section, Washington, D. 
2h 
Ceo 96093 
