10 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bllll. 



The External Morphology of the Diptera 



by G. C. Crampton, Ph. D.* 

 Massachusetts State Colletje 



Variations in Size 



It has been said that if all of the species of the animal kingdom 

 were arranged in an ascending series from the smallest protozoon to 

 tlie largest whale, a common housefly would be seen to be of average 

 size, and from this standpoint the average dipteran is not unduly 

 small, but most members of the order Diptera are of moderate size, 

 and do not, as a rule, exhibit wide variations in size within a single 

 family. 



Willi.-ton (1908)' states that the largest dipteran observed by him 

 was a Brazilian species of Mydas which measured 52 mm. in length, 

 while the smallest fly observed by him was a cecidomyid measuring less 

 than half a millimeter in length (the antennae were not included in 

 these measurements) ; and, as he points out, the Mydas fly was more 

 than a million times the size of the cecidomyid. Williston further 

 states that "In no single family of Diptera are the differences in size 

 anywhere nearly so great as those between the mydaid and cecido- 

 myid. Seldom do the differences in linear measurements in any one 

 family exceed ten fold." 



Perhaps the greatest wing expanse to be found in any dipteran 

 occurs in the Burmese tipulid, Gteyiacroscelis rex, which measures over 

 100 mm. from tip to tip of the expanded wings, while the North Amer- 

 ican tipulid, DasymolopMl'us ursinus, has a wing expanse of a little 

 more than 4 mm. The former is more than a thousand times the size 

 of the latter, and this difference in size is perhaps the greatest to be 

 found withm the limits of a single family, although the linear meas- 

 urements of the two tipulids would not bring out this fact, since the 

 forms m question are extremely elongated and slender. 



The largest and bulkiest representatives of the order are to be 

 found m the orthorrhaphous brachyceran families Tabanidae, Pantoph- 

 thalmidae,. Asilidae, Mydaidae and Cyrtidae, and in the cyclorrha- 

 phous family Syrphidae, while the smallest Diptera are to be found in 

 the nematocerous families Ceratopogonidae and Cecidomyidae. 



Variations in Form and Structure 



As a rule the Diptera are rather conservative in form, but wide 

 departures from the typical body habitus do occur among them, as 



*The writer wishes to make use of this opportunity of expressing- his sincere thanks 

 to Drs. C. P. Alexander and C. H. Curran for identifying the insects here figured, and 

 for many valuable suggestions during the preparation of this chapter, to Dr. Philip 

 Levereault for making many of the accompanying drawings, and to Dr. Inez Williams 

 for assembling many of the drawings and labeling the figures. 



