274 



THE GARDENER'S MONTHLY 



[September, 



Natural History and Science. 



CO MM UNI C A TIONS. 



CICADA SEPTENDECIM. 



BY C. V. EII.EY, WASHINGTON, D. C. 



Paragraphing is not conducive to accurate and 

 careful statement, and I often notice editorial 

 errors in the Gardener's Monthly— fewer, per- 

 haps, than in other magazines of similar char- 

 acter. In the short paragraph on Cicada, on 

 page 247 of the August number, there are two 

 technical errors anil an unjust reflection. The 

 seventeen-3'ear Cicada was named by Linnaeus 

 Cicada septendecim — not septemdecim, and the 

 thirteen-year race of it Cicada tredecim— not 

 tridecim— by mj-self. I did not describe it as a 

 new species, as you may see by reference to the 

 note (enclosed) on pp. 58-9 of Bulletin 6 U. S. 

 E. C, the General Index and Supplement to the 

 nine Missouri Entomological Reports. You may 

 deem the note of sufficient interest to your read- 

 ers to warrant reproduction. 



The popular term " Seventeen-year Locusts" 

 should be discountenanced, for while I agree 

 with much that you have said lately in your 

 magazine, anent popular names, this forms an 

 exception to the general rule, as I think I have 

 made sufficiently clear in my 7th Mo. Eep. 

 (pp. 187-8 ) 



"Cicada septemdecim (Rep. I, p. 18) — This or- 

 thography, used in the Reports, is grammati- 

 cally correct, but I find that Linnaeus himself 

 wrote septendecim (Systema Naturae, Tom I, 

 Pars II, 12Lh Ed. Stockholm, 1767). Fitch used 

 both forms of spelling, but Westwood, Harris 

 and most other authors follow Linnaeus, and sep- 

 tendecim is, therefore, preferable. As to whether 

 the seventeen and thirteen-year broods should 

 be considered specifically distinct, I am still of 

 the opinion expressed in the First Report that 

 the insects should not be looked upon as distinct 

 species, but that tredecim Riley should rather 

 be considered a race, or as Walsh (in a letter to 

 Charles Darwin, which has kindly been shown 

 me by Mr. G. H. Darwin) puts it, an incipient 

 species to which, for convenience, it is desirable 

 to give a distinctive name. That it may be 



looked upon as a good species by excellent au- 

 thority, will be seen by Walsh's discussion of the 

 subject (Ainei-ican Entomologist II, p. 33.5) which 

 I here quote: 



"What candid entomologist, who has worked 

 much upon any particular order, will not allow 

 that there are certain genera where it is often or 

 almost or quite impossible to distinguish species 

 by the mere comparison of cat)inet specimens 

 of the imairo? Loew and Osten Sack^n have 

 SMid this of the genus Cecidomyia in Diptera; 

 Osten Sacken of two other Dipterous genera, 

 Sciara and Ceratopogon ; Norton of the genus 

 Nematus in Hymenoptera; and Dr. LeConte 

 lately assured me that, although when he was a 

 young man, he thought himself able to discrimi- 

 nate in the closet, between the different species 

 of Brachinus in Coleoptera, he now considered it 

 quite impracticable to do so with any degree of 

 certainty. And yet who doubts the fact of 

 the existence, in North America, of very numer- 

 ous distinct species of Cecidomyia, of Sciara, of 

 Ceratopogon, of Nematus, and of Bnichinus. 



"Upon the same principle I strongly incline 

 to believe that the seventeen-year form of the 

 Periodical Cicada (C. septemdecim, Linn.) is a 

 distinct species from the thirteen-year form (C. 

 tredecim, Riley) although it has been impossible 

 for me, on the closest examination of very nu- 

 merous specimens, to detect any speci tic differ- 

 ence between these two forms.* It is very true 

 that the thirteen-year form is confined to the 

 more Southerly regions of the United States, 

 wliile the seventeen-year form is generally, but 

 not universally, peculiar to the Northern States ; 

 whence it has been, with some show of plausi- 

 bility, inferred that the thirteen-year form is 

 nothing but the seventeen-year form accelerated 

 in its metamorphosis by the influence of a hot 

 Southern climate. But as these two forms inter- 

 j lock and overlap each other in various localities, 

 i and as it frequently happens that particular 

 I broods of the two forms come out in the same 

 year, we should certainly expect that, if the two 

 j forms belonged to the same species, they would 

 ] occasionally intercross, whence would arise an 

 j intermediate variety having a periodic time of 

 ! fourteen, fifteen or sixteen years. As this does 

 ' not appear to have taken place, but on the con- 

 trary there is a pretty sharp dividing line be- 

 tween the habits of the two forms, without any 

 intermediate grades of any consequence, I infer 



* For an excellent statement of the facts bearing upon 

 this curious question, see a paper by Mr. Riley, the State 

 Entomologist of Missouri, in ZSo. 4 of the American Ento- 

 mologist, and a still more complete one in his First Annual 

 Report. 



