
but those following the first spraying gave rather clear-cut confirmation 
of "general observations." Im brief, there was evidence that the two high 
dosages (1.6-and 0.8) caused severe mortality, particularly of "tick-size" 
specimens, while the toll from the lighter dosages was less. A summary of 
enclosure findings following the first spray application is given below: 
1.6 dosage —— nearly complete mortality of tick-sized specimens; 
fairly heavy loss of large and medium-sized crabs. 
0.8 dosage —— 50-75% mortality of tick-size; less than 50% 
mortality of medium and large crabs. 
0.4 dosage —- some mortality (less than 50%) among various 
size classes. 
0.2 dosage -- about 25% kill in various size classes. 
Closing Burrows 
This technique consisted in counting the holes in a colony, 
covering them with a thin smear of mud and later noting the number of re- 
opened burrows. By this means it was thought that an index of active 
fiddlers might be obtained since each re-opened hole was assumed to 
represent at least one live crab. Contrary to expectations, this procedure 
did not confirm the observations obtained by the other methods. Indeed, 
there were some increases as well as decreases in the number of open burrows 
following sprayings. The reasons for such increases in areas of higher 
dosage application are not. apparent. Because of conflicting results, the 
data are not presented. 
Soil~Surface Sampling 
Though the soil-surface sampling procedure (see page 20) was 
designed and used primarily for studying populations of other small inver- 
tebrates in grassy areas, it also gave some information on numbers of fiddler 
crabs--usually small-sized ones—before and after spraying. Generally the 
number of fiddlers found in each foot-square sampling of the surface was 
too limited for the method to be significant by itself. 
In areas subject to the 1.6 and 0.8 pounds of DDT per acre, 
samplings taken two weeks after the first spraying showed a decrease of 
about 22% in live crabs compared to pre-spray samplings. At the same time, 
the low. dosage units showed no appreciable change in populations after 
_ spraying. The second application resulted in a similar though smaller 
decrease in the high dosage.areas. In contrast, no dead crabs were found 
in pre-spray samples of treated areas or in any check area samples. 
19 
