specimens from 1894, a few from tlie first decade 

 of the IQOO's, and a few collected in central Illinois 

 over the next 50 years. 



In 1956 the Northern Illinois Brood (Marlatt's 

 XIII) again emerged in high numbers and inspired 

 Henry S. Dybas of the Field Museum of Natural 

 History, Chicago; Thomas E. Moore, then at the 

 Illinois Natural History Sur\'ey, Urbana; and Richard 

 D. Alexander, formerly of White Heath, Illinois, to 

 begin new studies on cicadas. Their discoveries caused 

 renewed interest in these insects, opening new types 

 of inquiry and leading to new conclusions on the 

 nature and origin of the possible species involved and 

 the broods. They, along with Monte Lloyd, D. 

 Dwight Davis, and James Heath, made and are 

 making in-depth studies on the exact niches of the 

 species, their songs, and their possible dispersal after 

 deglaciation. 



EXCLUDED BROODS 



Several broods besides those whose distribution is 

 treated here were purported by Marlatt and others 

 to occur in Illinois. One of these, Marlatt's XIV, 

 was said to extend across the northern border of 

 Illinois. Although observations on periodical cicadas 

 of Illinois have not been regularly made until recent 

 times, the lack of records of this brood in the INHS 

 collections has some significance. Alexander &: Moore 

 in 1957 (an emergence year for Brood XIV) did record 

 single specimens in Illinois and Iowa, but they con- 

 sidered these cicadas to be stragglers from the previ- 

 ous vear's emergence of the Northern Illinois Brood 

 (Marlatt's XIII) (Alexander &: Moore 1962:18). Very 

 few cicadas were found in intensive searches in 1974, 

 and this fact, coupled with the negative evidence of 

 pre\ ious years, would indicate that Brood XIV does 

 not, and probably never did, occur in Illinois. 



Another brood (Marlatt's XII) reported by Mar- 

 latt (1907) to be in Illinois almost certainly does 

 not exist in our state, if indeed it is a valid brood 

 anywhere in the USA. In 1972, when this brood was 

 to emerge, I made repeated trips to Jo Da\iess 

 County and neighboring counties, and enlisted the 

 help of naturalists, state park rangers, and landowners 

 in attempts to locate populations of this alleged brood. 

 No cicadas were found. Marlatt, himself, felt that this 

 was a doubtful brood and reported that Forbes had 

 failed to locate it in northwestern Illinois. Probably 

 the records of this brood in Illinois were based on 

 precocious cicadas of the Northern Illinois Brood 

 (Marlatt's XIII) which emerged a year early. 



Marlatt's I was recorded by Marlatt (1907) as 

 being questionably present in Madison County, but 

 the Illinois Natural History Survey has no records or 

 specimens of this brood. Alexander & Moore (1962) 



did not list any Illinois records of this brood, which 

 they studied in detail in the East in 1961. 



Marlatt's VI was purported to occur in Illinois 

 from localities where cicadas were said to have 

 emerged in abundance in 1898. In the S.A. Forbes 

 correspondence of 1898 in tlie archives section of 

 the University of Illinois Library is a request from 

 L. O. Howard of the Bureau of Entomology, Wash- 

 ington, D.C., for cicada information. This request 

 prompted Forbes to send a circular letter to teachers 

 and superintendents of schools asking for data on 

 cicadas emerging in 1898. Besides Forbes, Howard 

 asked other correspondents for information on these 

 cicadas. By June 20, 1898, Howard informed Forbes 

 that he had received a large amount of data from 

 Illinois. The records received by Forbes and Howard 

 from Crawford, Jackson, Jasper, Lawrence, Perry, 

 Pulaski, Union, Wabash, and Wayne counties can be 

 referred to the Lower Mississippi River Valley Brood 

 (Marlatt's XXIII), and this distribution fits well with 

 our present-day records. The other records reported 

 by Howard, especially those supposedly of Marlatt's 

 VI in central Illinois, must be considered doubtful, 

 as we have no specimens in the Natural History 

 Survey collection from this region in 1898 or the 

 following years during which this brood appeared. 

 It should have reappeared in 1966 if it really exists 

 in Illinois, but no observers at the Illinois Natural 

 History Survey have any notes or recollections of 

 this brood's emerging at that time. 



THE SPECIES OF PERIODICAL CICADAS 



During the years when the surveillance of periodi- 

 cal cicadas was dominated by Riley and Marlatt, it 

 was generally thought that two races existed, the 

 17-year cicada, Tibicen (Cicada) sepiendecim (Lin- 

 naeus), and the 13-year cicada, Tibicen (Cicada) 

 tredecim Riley, with a dwarf form known as cassini 

 Fisher. Walsh argued (Marlatt 1907:17; Lloyd & 

 Dybas 1966fe), and even corresponded with Charles 

 Darwin on the subject, that the 13-year race was an 

 incipient species because the 13-year race and the 

 17-year race occasionally have opportunities to inter- 

 breed; yet no intermediate emergences (14-, 15-, or 

 16-year intervals) result. 



In 1931 Reamer, in 1958 Alexander & Moore (see 

 also Moore &c Alexander 1958), and in 1962 Dybas 

 & Lloyd, on the basis of morphological and behavioral 

 distinctiveness, independently arrived at the conclu- 

 sion that Magicada septendecim and M. cassini were 

 separate species. In 1962 Alexander & Moore recog- 

 nized six full species, M. septendecim, M. cassini, and 

 M. septendecula Alexander and Moore for the 17-year 

 broods, and M. tredecim, M. tredecassini Alexander 

 and Moore, and M. tredecula Alexander and Moore 



