Insects at Rebecca Shoal and Tortugas. 211 



100, but during the two days spent there the past season only 2 were 

 seen, 1 of them being captured. At Loggerhead on July 19 a single 

 individual was the reward of a day's lookout, and only 3 were seen 

 there until the morning of July 30, when, as we were closing the labora- 

 tories preparatory to leaving the island, the air over the bay-cedar 

 bushes near the buildings was alive with dragon-flies. I counted a 

 score hi sight at one time. 



Now, since there is no possible breeding-place for Odonata upon any 

 of the Tortugas Islands, it is plain that the great variation in numbers 

 must be due to their migratory habits; for it is not likely that boats 

 or other agencies are responsible for their introduction. As an example 

 of the tenacity with which dragon-flies follow vessels upon which they 

 may chance to be carried from shore, the case may be cited of a large 

 specimen observed flying about the superstructure of the steamship 

 Concho just before it left the dock at Key West. This insect, or one of 

 its species, was noted on the following day while the boat was passing 

 through the Straits of Florida. It was still on board when, toward 

 the end of the voyage, the vessel was within 100 miles of New York. 



Occasionally single specimens of Lepidoptera appear at Tortugas as if 

 brought involuntarily from distant haunts. On July 28 a Sphingid, 

 Sesia tantalus Linnaeus, was captured while feeding on lilies near the 

 laboratory. While certain species apparently breed on Loggerhead 

 and East Keys, others are so rare as to indicate that they are immi- 

 grants. Dr. Mayer is authority for the statement that one of the larger 

 Noctuidse often comes to Tortugas on southerly winds from Cuba. 



DO SARCOPHAGID/E BREED AT TORTUGAS? 



Conspicuous by their numbers on the open sandy shores and among 

 the vegetation closely bordering them at Tortugas are two species 

 of Sarcophagidae or flesh-flies. Mr. R. R. Parker has identified the 

 larger as Sarothromyia femoralis Schiner, and the smaller as Sarcopha- 

 gula occidua Fabricius. Like most of the insects inhabiting these white 

 beaches where the light is intense, both species are much lighter in color 

 than ordinary members of the family. Their flight is also peculiar in 

 so far as I am familiar with the group. As one walks along the beach 

 these flies dart into the air only to alight a few feet in advance, repeat- 

 ing these short flights almost as a series of hops if disturbed by the 

 progress of the intruder. I was unable to cause an extended flight. 

 The possibility was suggested that their powers of flight had been modi- 

 fied after dwelling for some time on these isolated keys. If such were 

 true then certainly they must be breeding there, for their numbers are 

 considerable. 



An experiment was performed in order to ascertain whether or not 

 these Sarcophagids would breed in dead land-crabs. On July 19 a glass 

 jar containing 3 inches of sand and a freshly killed ghost crab, Ocypoda 



