THE PERIODICAL CICADA BY WM. J. GERHARD Associate Curator of Insects FIELD MUSEUM OF NATURAL HISTORY CHICAGO 1923 THE PERIODICAL CICADA. FROM AN EXHIBIT IN FIELD MUSEUM OF NATURAL HISTORY, SHOWING THE VARIOUS STAGES OF THE INSECT AND THE INJURIOUS EGG-LAYING HABITS OF THE FEMALES. Field Museum of Natural History Department op Zoology CmcAoo. itts Lbatlbt Numbbb 4 The Periodical Cicada The Periodical or Seventeen-year Cicada, com- monly but improperly called the "seventeen-year locust," is one of the most noteworthy insects found in North America. Its sudden appearance at inter- vals in large numbers in different parts of the eastern United States, the indescribable din caused by the multitude of singing males, and the conspicuous evi- dence of the damage the females do to deciduous trees, invariably arouse widespread attention and much fear concerning its destructive habits. The Periodical Cicada is a true bug and, like the other members of the order Hemiptera, has a jointed beak fitted for piercing the tissue of plants. The name locust, so commonly applied to it, is improper, because almost since the beginning of history it has been used to designate wholly different insects, namely, grasshoppers, which have biting mouth-parts and which are not closely related to cicadas. The use of the same name for two dissimilar insects, no doubt, is the result of confusing the cicadas with the devas- tating locusts of the old world and the destructive locusts or grasshoppers of the United States. Not only is this insect noteworthy on account of its periodic appearance in immense hordes, but it is remarkable for the extraordinary duration of its life in the larval and pupal stages. In the Northern States its immature stages extend over a period of seventeen years; in the South, thirteen years are [41] 2 Field Museum op Natural History required for its underground existence. It is the only insect that is known to live for so long a period. The sound-producing organs of the adult male are likewise wholly different from those of other insects, in no way resembling the stridulating apparatus of grasshoppers, katydids and crickets. Like most insects, the Periodical Cicada passes through four stages during its life cycle, namely, the egg, larval, pupal and adult stages. Although some of the facts of the life-history were known to the early colonists, it was only during the latter half of the last century that much progress was made in solving many of the problems concerning this inter- esting cicada. Thus, for a long time it was difficult to account for the appearance of various broods in different sections of the country at intervals shorter than the customary seventeen-year period. The ex- planation became simple when it was ascertained that there were two races of this insect, one in the North- ern States requiring seventeen years for its life cycle, a southern one developing through all of its stages in thirteen years. On account of the difference in the duration of the life of the northern and southern races, at one time it was thought that there were two species of the Periodical Cicada in America. For this reason dif- ferent specific names were assigned to them. A name was also proposed for the small, dwarfed individuals that are found among nearly every brood. But as no constant, structural characters have been found to separate the three so-called species, entomologists now consider them to be one species, which they designate as Tibicina septendecim, with a southern race, tredecim, and a small form, cassini. By means of the many, scattered notes and records, extending back over two hundred years, and the more [42] The Periodical Cicada Distribution of the broods of the 17-year race of the Periodical Cicada (after MarlaU). Distribution of the broods of the 13-year race of tha Periodical Cicada (after ICarlatt). [a] 4 Field Museum of Natural History recent, careful observations, it has become possible to trace out thirty broods of the Periodical Cicada. Seventeen broods belong to the northern race; thir- teen to the southern. These broods vary greatly in the number of individuals and in the range of their distribution. For example, Brood XI (1920) is very small and appears only in a few sections of Massachu- setts and Connecticut, whereas Brood X (1919) is recorded from at least fourteen states, in four of which, namely, Indiana, Ohio, Maryland and south- eastern Pennsylvania, it appears in dense swarms. Northern Illinois is within the range of only one large or dense brood, and that is the rather compact Brood XIII, which was so much in evidence during the summer of 1922. With the exception of a few records of individuals in some other states, this brood is distributed over the northern half of Illinois, eastern Iowa, southern Wisconsin and Michigan and north- western Indiana. The two maps on the preceding page indicate the distribution of all the broods of the two races. It will be noted that the range of the two races overlaps for a short distance, particularly in southern Missouri, Ken- tucky, Tennessee, Illinois and Indiana. If the differ- ence in the duration of the immature stages of the two races were wholly due to climatic conditions, it would be natural to expect to find a gradual decrease in the time of development of the northern race as it approaches the northern limits of the southern race. This, how- ever, is not the case. Seemingly the time of develop- ment, while no doubt originally influenced by climatic conditions, has become fixed for the species or race as a whole and is now not permanently modified by slight differences in temperature. That the duration of the life of this cicada is sometimes either acceler- ated or retarded is quite evident, for not infrequently [44] The Periodical Cicada 6 a few adults emerge a year before the main brood is due, or they may appear a year later. To account for the existence of the various broods today, the plausible theory has been advanced that originally, many centuries ago, there was but one brood for each of the two races and that they ap- peared throughout their entire range once every sev- enteen or thirteen years. But as accelerated or be- lated individuals increased in number, extended their range and resumed their normal life cycle, there were started the various broods that are now recognized. According to this hypothesis, if the breeding places do not become too limited and no other detrimental fac- tors arise, the different broods will increase to such an extent in the distant future that this insect will appear every year throughout its entire range. The newly hatched larvae, or young, of the Periodi- cal Cicada are pale, minute, active creatures with thick forelegs well-fitted for digging and a jointed beak well-suited for piercing small roots. On emerg- ing from the egg, which will be described later, the young drop lightly to the ground and work their way into the soil for a short distance. Near some rootlet each larva encloses itself in a little, isolated, earthen cell which is enlarged as the young increases in size. It is not probable that they move about in the ground for any great distance, but just how they really pass this long, dark period of their life is not known and obviously is difficult to ascertain. Since their cells are nearly always found in close contact to a root or rootlet, it is believed that the immature cicadas feed mainly upon the juices of small roots. The depth to which the larvae burrow varies from six to twenty- four inches. There are, however, records of some that were found four feet or more beneath the surface of the soil. During their long, subterranean existence [46] 6 Field Museum of Natural History they grow slowly and moult or shed their skin at in- tervals of several years. Some time after the fourth moult, when the larvae (of the northern race) are about twelve years old, they change into the first of their two pupal stages. The pupae of the Periodical Cicada, unlike those of the majority of insects, rather closely resemble the larvae. They likewise are quite active and continue to feed upon the juices of roots. Early in the spring, or during the latter part of April, a few months less than seventeen years after the young of the northern race began their subterranean life, the pupae, seem- ingly all of them at the same time, burrow upward toward the surface of the ground. At first the exit burrows or cells may end just below the surface, under logs, stones, chips, or leaves ; but under certain conditions the pupae erect tube-like chimneys or tur- rets of clay that extend from two to six inches above the ground. An astonishingly large number of larvae and finally pupae sometimes inhabit a limited area of the soil. As many as twenty-five chimneys or turrets have been found on one square foot of ground, and nine thou- sand burrow exits have been counted under one tree. The exodus from their burrows occurs generally after sundown during the latter part of May and the fore part of June. During one evening myriads of pupae, as if impelled by an irresistible force, leave their burrows and turrets and climb up on any nearby object. Some crawl up on plants less than a foot in height, while others may ascend trees for a distance of fifteen or more feet. On reaching a favorable spot, they rest quietly for a short period, their thick, front legs clinging tightly to their support. Shortly after it has become dark, the interesting transforma- tion begins. A longitudinal slit first appears along [46] The Periodical Cicada 7 the middle of the forepart of the pupa's back. This opening gradually widens as the pale adult slowly emerges and leaves the empty pupal skin attached to a leaf, twig or branch. The freshly emerged adults are rather ghostly creatures, soft, flabby, creamy white in color, with reddish compound eyes and two, black, rectangular spots on their back just behind the head. At first the wings are merely little, wrinkled, whitish pads with an orange tinge at their base, but they soon ex- pand to their final size. The entire body then be- gins to harden and to assume the characteristic color of the species. A few hours after sunrise on the morning following their transformation, the adult cicadas are ready to commence their short but active career, lasting only from four to six weeks. Until a comparatively recent date it was believed that no food was taken by the Periodical Cicada in the adult stage. It is now known, however, that it does feed upon the sap of trees, the branches of which it pierces by means of its beak. Whether the taking of food is really essential for mating and egg-laying is still an open question. For obtaining liquid nour- ishment its mouth-parts are well fitted. Instead of having biting jaws, it possesses a jointed, beak-like lower lip which encloses fine, elongated, stiff, piercing organs that, with their beak-like sheath, convey the sap to the mouth cavity. Under favorable conditions, this insect could readily pierce the human skin by means of its beak, but apparently it rarely or never attempts to protect itself in such a manner. The egg-laying habits of this cicada are of consid- erable interest, and to them is due most of the dam- age caused by this insect. The female inserts her eggs in the twigs and branches of trees by means of a strong, curved ovipositor which extends from the [47] 8 Field Museum of Natural History underside of the abdomen. The main part of the ovipositor consists of three, horny pieces, two of which are serrated and spear-shaped at the tip, and by a backward and forward movement are able to make a series of punctures in hard wood. Despite a behef to the contrary, the ovipositor is not a sting, and it is doubtful whether it is ever used as a means of defense. The eggs of the Periodical Cicada are whitish, cylindrical and about one-twelfth of an inch in length. They are inserted just below the surface and are in- clined forward at an angle of 45 degrees. With her ovipositor the female makes a series of punctures, generally on the under side of the twig, about half an inch in length, and in them she then lays a longitudinal row of eggs in pairs. Without changing her position on the twig, she makes another series of punctures along side of the first, so that finally each egg nest in the twig consists of two more or less parallel rows of eggs, from ten to eighteen in number and separated by a thin partition. Beginning toward the base of the twig, which commonly is one of the previous year's growth, she works toward the tip, or occasion- ally toward the base. Sometimes the egg nests are so close together that they appear to be continuous. One twig after another is supposed to be pierced in the manner described until the female has laid her batch of eggs, which may number from two to six hundred. The eggs are laid in a large variety of trees, bushes, and sometimes in herbaceous plants. Oak trees, either young or old, seem to be preferred, possibly because in most woodland tracts they predominate, and, therefore, are the most accessible. Pine trees appear to be exempt, the gummy sap exuding from the punctures, no doubt, being detrimental to the hatch- ing of the eggs. [48] The Periodical Cicada 1. Era. 2. Newly hatched Urva. 3. Full srrown Urva. (Fourth staffe) 4. Pupa (tecond ttase). (Very similar to ftrtt staare) 6 and 6. Body of males. (Showintr sound organs at A) 7. Body of famala. (Showing ovipositor) 8. Adult female. 9. Essr nests in twlar. (Fiff*. 1. 2 and 3 greatly enlarged, after Marlatt; figs. 4-9 slightly reduced.) [491 10 Field Museum of Natural History The results of the cicada's egg-laying habits vary with different trees. The oaks show the effects most conspicuously; the leaves beyond the first punctures turn brown, and many of the twigs become so weak that they are broken off by the wind. Under the less hardy oaks the ground is sometimes almost covered with dead terminal twigs. A few weeks after a large brood has emerged, tracts of oak woodland ap- pear as though they had been scorched by a forest fire. But some trees withstand the effects of the punctures fairly well, though the egg nests are prone to leave scars that eventually produce a weak spot in the growing branch. The Seventeen-year Cicada fortunately appears mainly and most abundantly in woodland tracts, places where its injurious habits do not result in an appreciable, monetary loss. It likewise does not fly far from its breeding grounds. Nevertheless, it often does much harm to fruit trees. This is particularly the case wherever orchards and nurseries are located near wooded areas in which the cicadas may be nu- merous. Not only is nursery stock sometimes badly injured, but frequently young trees die from the re- sults of the egg punctures. A few days after a large brood of cicadas has emerged from the ground, the air resounds with the peculiar, whirring noise caused by the countless males. It is only the male that is capable of making the characteristic buzzing sound; and no other in- sects, except those belonging to the cicada family, have a similar musical apparatus. The sound organs occupy nearly the entire basal segment of the abdo- men. The most conspicuous of these organs are two, covering flaps or opercula, visible only from below, and two tense, ribbed drum-like membranes which are vibrated by two powerful muscles. By raising [ยป] The Periodical Cicada U and lowering the abdomen, thereby changing the posi- tion of the opercula, as well as in other ways, the nature of the song is changed at will. So distinctive is the sound produced by the various species of cicadas, that a student learns to recognize many of them by their song alone. The family Cicadidae, of which the Periodical Cicada is the most noteworthy member, belongs to the order Hemiptera, which comprises the true bugs or those insects having a jointed beak fitted for piercing and sucking. The family is well represented throughout the tropical and temperate regions of both hemis- pheres, over eight hundred species having been described. Of this number one hundred and thirteen are listed from America north of Mexico. All of the females lay their eggs in the tissues of plants or trees ; all of the males have the complex, sound organs, and are considered to be the noisiest insects in the world; but, with the exception of the Periodical Cicada, so far as known, not one of them requires more than two years for its development from the egg to the adult stage. The Dog-day Harvest-fly or L5rreman is one of the common cicadas that is heard every summer. As it is two-brooded, the adults appear every year. The cicadas are fairly large, four-winged insects, with a blunt head, three-jointed beak arising near the base of the lower surface of the head, prominent compound eyes, three simple eyes or ocelli, and an ab- domen consisting of six segments. The front legs are much thickened and armed with a spine beneath. The wings are of a similar texture throughout, and when at rest extend roof-like over the body. In the tropics many of the species are brightly colored, but in the United States they are mostly greenish marked with red and black. [61] 12 Field Museum of Natural History There is no conclusive evidence apparently that the immature Periodical Cicada does very much injury to plants or trees during the long period that it feeds upon the juices of small roots. It is, therefore, only in exceptional cases, or in very limited areas, that it might prove desirable to destroy the young. Accord- ing to Dr. Marlatt, the most satisfactory method of killing the larvae is the use of bisulphide of carbon in- jected into the soil where it is known they are quite numerous. In the adult stage the females unquestionably are very harmful to various trees and shrubs, though the damage they do is probably not nearly so extensive as is generally supposed. On oak trees, at least, the results of their egg-laying habits are much in the nature of a pruning. But in orchards and nurseries the trees are sometimes injured so severely that some means of protecting or saving them and destroying the cicadas must be adopted. On account of the myriad of individuals over a wide area and the short life of the adults, the usual methods of destroying noxious insects are not always practi- cal. The use of repellents to prevent the females from ovipositing has likewise not met with much success. When the adults emerge near orchards or nurseries, young fruit trees should, if possible, be protected by netting, and the cicadas resting thereon should be col- lected and killed every morning and evening, when they are somewhat sluggish. As the egg nests or scars often serve as openings for other destructive insects, it is quite essential to take proper care of young injured trees. In limited areas, like parks and yards contain- ing shade trees and shrubbery, the emerging and adult cicadas can be readily killed by spraying them with a strong kerosene emulsion. Even the pupae are not immune to an emulsion of kerosene, soap and [52] The Periodical Cicada 18 water. Since the various broods are known to appear during a definite year in different places, it is obviously unwise to plant nursery stock or orchards near wood- land when this insect is soon due. Although the Periodical Cicada may not appear to be decreasing in number to the casual observer, there is sufficient evidence to indicate that it is not nearly so abundant in many places as it was years ago. Mites and other insects prey upon it in its various stages, and very many of the rather helpless adults are de- voured by birds, especially the English sparrow. But the most potent factors that are reducing their num- ber are the diminishing woodland areas and the clear- ing of land for cultivation. It is, therefore, not im- probable that in the distant future this long-lived in- sect may be exterminated by the agricultural devel- opment of the country. Wm. J. Gerhard, AssoeuUe Curator of Insects. [68]