F. M. Carpenter.
Early Insect Life.
Psyche 54:65-85, 1947.

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PSYCHE
VOL. 54 JUNE, 1947 No. 2
EARLY INSECT LIFE*
BY FRANK M. CARPENTER
Harvard University
Most entomologists, whether concerned with insect con- trol or taxonomy, are convinced that we have enough living insects to contend with, without bothering about those of prehistoric times. Paradoxical as it may be, how- ever, man apparently owes his very existence to the early insects. Some three hundred million years ago, as the first Amphibia abandoned the aquatic environment of their ancestors and explored the possibilities of terres- trial life, they were obliged to find a new source of food. By that time, the insects had already become established on land and, being especially abundant near water, were readily available to them. The amphibians were thus able to survive in their new environment and eventually their descendants gave rise to reptiles, birds and mam- mals,. Many geologic periods later-only a few million years ago, in fact-man evolved within the mammalian complex. Cannot the insects claim, therefore, that if it were not for their early ancestors, the vertebrates might have failed to gain a foot-hold on land and man might not have come into existence?
Let us consider the nature and extent of the early insect life to which we presumably owe so much. "Early" is of course a relative term, and to define my present use of it, I must refer to the conventional geologic timetable. Figure 1 lists the eras and periods of that part of geologic time with which paleontology is chiefly concerned. Of the three eras, the Paleozoic is the earliest and longest, * Annual Public Address of the Entomological Society of America, Rich- mond Virginia, December 9, 1946. Published with the aid of a grant from the Museum of Comparative Zoology at Harvard College. 65
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66 Psyche [June
beginning about 550 million years ago and extending up to some 190 million years ago. For convenience, it is divided into six periods of unequal duration, their limits being arbitrarily set with reference to extensive geologic events. In this account of early insect life, I am refer- ring only to the insects of the Paleozoic era-from the first appearance of the group through the Permian Period.
The question of the oldest geologic occurrence of any group of organisms is always a controversial one, for much depends on interpretation of fragmentary material TABLE OF GEOLOGIC PERIODS
APPROXIMATE TIME
ERA 1 PERIOD
1 IN MILLIONS OF YEARS)
SINCE BEGINNING
OF PERIOD
CENOZOIC QUATERNARY
(AGE OF MAMMALS AND MAN)
T~RTIARy 1 6;
TRIASSIC 35
PERMIAN 1 25
PALEOZOIC
(AGE OF INVERTEBRATES AND
PRIMITIVE VERTEBRATES)
DEVONIAN
SILURIAN
ORDOVICIAN
Figure 1. Table of ~eolo~ic Periods. (Adapted from Rorner's Verte- 'brute Paleontology, University of Chicago Press.) and the definition of the group.
Handlirsch showed in
1906 that the fossils described as insects from strata older than those of the Upper Carboniferous Period were not insects at all; and he concluded that the earliest record of the class was in the lower part of that period. During the past forty years discovery of three older insects has been announced. Two of these, identified as Collembola, have been described from Devonian rocks, the Rhynie Chert, of Scotland.' Without going into details, we can 1 R. J. Tillyard, Trans. Ent. Soc. London, 1928: 65-71; H. Womersley, Victorian Naturalist, 1934, vol. 51: 159-165; D. J. Scourfield, Proc. Linn. Soc. London, 152 sess., 1939-40 : 113-131.



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19471 Early Insect Life 67
state that these fossils are very fragmentary, the largest specimen being only about a millimeter long. Many parts of the head and thorax have been found, but since only the first three abdominal segments are known, there is no evidence that the collembolan "spring" was present, or that the abdomen consisted of but six segments, as in living Collembola. Consequently, although such eminent authorities as G. H. Carpenter and H. Womersley have accepted the specimens as Collembola, I believe that doubt about their relationship will exist until additional fossils have been found showing those two characteristic fea- tures of the Collembola. As a matter of fact, as Imms and others have pointed out, the Collembola are not true insects-that is, although hexapodous arthropods, they arose independently from pre-insectan types. The possi- ble occurrence of Collembola in Devonian rocks, there- fore, has no direct bearing on the earliest record of true insects.
The other discovery of an insect in rocks older than the Upper Carboniferous was announced by the French paleontologist, Dr. Pierre Pruvost, in 1919. The speci- men concerned was found in Lower Carboniferous strata of Nova Scotia (Horton's Bluff), and identified by Pru- vost as a member of the extinct Order ~a1ffiodict~o"ptera.~ However, examination of this fossil, which is now in the Peabody Museum at Yale University, convinces me that it is in reality part of a plant stem. A similar conviction was expressed by Dr. David White,3 then paleobotanist of the United States Geological Survey, who studied the specimen shortly after it was found, although he did not publish his conclusion.
According' to our present knowledge, therefore, the earliest unquestionable insects occur in Upper Carbon- iferous strata. This first occurrence is not extensive, but it does indicate the approximate time of origin of the insects. Let us return for a moment to the geologic time- table, and examine in more detail the Upper Carbonifer- ous Period (Figure 2). This represents an interval of 2 La Faune continentale du terrain Houiller du Nord de la France, p. 283. 3 In a letter dated May 11, 1914, and on file in the Peabody Museum.



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PERIOD STAGES
Psyche [June
INSECT ORDERS
Coleoptera
Thysanoptera, Perlaria
Protope~la~ia, P~otelytroptera~
Ephemerida, Odonata,
Corrodentia, Hemiptera,
Mecoptera, Neuroptera
Megasecoptera, Calonewodea
Palaeodictyoptera, Blat taria
Protodonata, Protorthofitera
Figure 2.
The First Occurrence of Insect Orders in the Permian and Carboniferous Periods.
Names of exinct orders are italicized.




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19471 Early Insect Life 69
about thirty-five million years, and on the basis of its flora and fauna, is divided into three main stages, the Upper Namurian, Westphalian, and Stephanian. The record of insects is very scanty in the oldest of these; not until the late Westphalian and Stephanian rocks are insect re- mains sufficiently abundant and preserved to give us a concept of the fauna. Nevertheless, three species are known from the Upper Namurian, at the very base of the Upper Carboniferous, and they constitute the earliest record of the insects. One of these (Emsiptern Zarischi Pruvost), from Czechoslovakia, consists of part of a wing, which, though incomplete, clearly belongs to a member of the extinct Order Protodonata, related to the Odonata. Another fossil (Stygne roemeri Handl.), from Germany, is a nearly complete wing with orthopteroid features that place it in another extinct order, the Protorthoptera. The third specimen (Metropator pusillus Handl.), from Penn- sylvania, is a very fragmentary wing which might have belonged to any one of several orders. Now this is truly a meagre record, but it does reveal two facts : first, insects with fully developed wings existed in the earliest part of the Upper Carboniferous Period, about 250 million years ago; and second, at least two orders, widely separated phylogenetically, occurred at that time. We can infer from this 'ecord that insects must have arisen at least as far back as the Lower Carboniferous in order for such di- versity to be attained by the beginning of the Upper Car- boniferous. This inference becomes even more obvious, when we bear in mind that morphological studies have shown that the most generalized or primitive insects were wingless, like the Thysanura. Apterous species must have existed, therefore, even before the winged ones. So much for the first record of the insects. Let us now
briefly consider the development of the class during the rest of the Paleozoic era. Referring again to the Upper Carboniferous table (Figure 2) we find that as we go up through the several stages, additional orders appear, and there is an increase in the total number of orders. From the lower half of the Westphalian stage (A and B) there are forty species known, representing the two orders



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70 PsYc/%~ [June -
previously mentioned (Protodonata and Protorthoptera), as well as the extinct order Palaeodictyoptera and the existing order Blattaria or cockroaches. In the upper half of the Westphalian stage (C and D), about 15 million years after the first record of the insects, we come to the level of the Mazon Creek nodules in Illinois, second only to the Commentry shales in France as a source of Carbon- iferous insects. From this part of the Westphalian more than four hundred insects are known, representing the four orders already mentioned and in addition two other extinct ones, the Megasecoptera and Caloneurodea. From the Stephanian stage, which includes the Commentry de- posit, about fifteen hundred species have been described, belonging to the orders previously mentioned as well is still another exinct one, the Protohemiptera. Thus, we see that by the end of the Upper Carboniferous seven orders of insects had come into existence, of which one, the Blattaria, survived for some two hundred forty mil- lion years to the present time.*
Let us now continue into the Permian Period (Figure Z), which represents an interval of about twenty-five mil- lion years. In the lower or oldest strata of the period eight orders have been found in addition to the seven which have persisted from the Carboniferous. Two of these, the Protoperlaria and Protelytroptera, are extinct, but the others are living orders. These are the Ephem- erida, Odonata, Corrodentia, Hemiptera, Mecoptera, and Neuroptera. This fauna was an extremely interesting one, combining as it did eight extinct and seven existing orders. The Lower Permian was the last time, so far as our records now show, that the extinct orders out- numbered the existing ones. In Middle Permian rocks, Thysanoptera and Perlaria have been found.; and in upper Permian strata the Coleoptera appear. These make a total of eighteen living and extinct orders of insects which came into existence before the end of the Paleozoic era, about two hundred million years ago ; and of these ten are still living.
4 I have not included in this account several extinct orders which are based upon very fragmentary specimens.




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19471 Early Insect Life 71
This brief survey gives an idea of the extent of the early insect life. The fauna was obviously a complex one- probably more so than we fully realize, for our present roster of the orders existing at the time is surely far from complete. Nevertheless, the variety of insect types proba- bly fell far short of that which exists now, their biological environment being relatively simple. The plants of the time were largely seed-ferns and other gymnosperms ; angiosperms were entirely absent, and, incidentally, did not arise for many millions of years later. It is difficult for us, living at a time when angiosperms dominate the plant world, to imagine a time of their complete absence; and equally difficult to imagine an extensive insect fauna without them. Also, there was a complete absence of birds and of mammals. Insects were then the only flying creatures on earth; they could readily escape by flight from their amphibian and reptilian enemies without danger of pursuit. Certainly the life of the insects must have been very different then from what it is now-with birds, bats, man, and DDT.
Our knowledge of the habits, life histories, and food of these early insects is necessarily slight, but certain infer- ences can be made from their structure, as we now know it. Let us see what this was like and what conclusions can be reached.
The order Palseodictyoptera, which existed during the Upper Carboniferous and Permian, is a negative and ill- defined group. Attempts to divide it into two or more orders have not proven successful, because some species seem to merge into the Ephemerida, and others into the Orthopteroids. Nevertheless, I believe that most of the one hundred fifty species which have been described are members of one order. Their closest living relatives are the Ephemerida and, to a lesser extent, the Odonata. The fact that all complete specimens are preserved with their wings outspread shows that, like the Ephemerida and Odonata, they were palaeopterous, i.e., unable to fold their wings back over the abdomen at rest. They had nearly similar fore and hind wings and were apparently weak fliers. Although they are mostly preserved as isolated



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72 Psyche [June
wings, enough whole specimens have been found to give us a slight knowledge of their body structure. They were
primitive insects, probably more so than any other known winged insects, but they did have some specializations. It should be noted, in this connection, that no remains of bodies of any insects have been found in the older half of the Upper Carboniferous strata.
Not until "we come to the
Mazon Creek deposits, about 15 million years after the first record of the insects, are body remains known. This
probably would have provided ample time for extensive specialization to develop. At any rate, the Palseodicty- optera were more primitive than any winged insects now living.
They show about the same range in size as living dragonflies, many having a wbg expanse of about two inches.
The head was relatively small; the mouth-parts mandibulate and inconspiauous.
Their antennae are un-
known, except for the proximal segments ; probably they were moderately long and multisegmented. The thoracic
segments and legs were nearly homonornous. The most striking characteristic of the Palseodictyoptera was the presence of paired membraneous lobes on the prothorax ; these resembled miniature wings and are usually con- sidered homologues of the functional meso- and meta- thoracic wings. The abdominal segments showed little differentiation, and the abdomen terminated in a pair of long, multisegmented cerci.
Well preserved specimens
have paired lateral lobes on each abdominal segment. The immature stages of the Palaeodictyoptera, are com- pletely unknown. Several vague and fragmentary speei- mens, which are probably insect nymphs of some sort, have been assigned to the Palseodiet~optera, but they could just as well belong to certain other groups. The paired abdominal lobes of the adult have been generally interpreted as vestigial tracheal gills of the nymphs. This of course implies that the nymphs were aquatic; and in view of the close relationship between the Ephemerida and Odonata, both of which have aquatic nymphs, we may infer this to have been the case. From this vou will see that our knowledge of the Palseodictyoptera is not great. Their general activities were probably much like those of



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Early Insect Life
the present-day may-flies, crawling and fluttering among the plants bordering the ponds or swamps in which their nymphs developed-inoffensive creatures whose only claim to fame is their antiquity and proximity to the great ancestor of all insects. They had no defense against the more powerful, predaceous insects which developed dur- ing the later Carboniferous and Permian, and for which they must have been easy prey.
Related to these Palseodictyoptera was another order of ephemerid-like creatures, termed the Megasecoptera. They were small to large insects, with a wing expanse ranging from one-half to five inches, and, like the Palseo- dictyoptera, they were unable to fold their wings over the abdomen. Until about 12 years ago they were known exclusively from the Upper Carboniferous; many Per- *
mian species have since been found, and it has become apparent that the order did not attain its greatest devel- opment until that period. They had moderately long an- tennae, and extremely long cerci. In the Carboniferous- species the head was small and short, but in some of the Permian types it was prolonged into a rostrum, probably much like that of the scorpion-flies. The older forms had mandibulate mouth-parts, and this was probably true also of the later species. The thorax and abdomen were slender, and, in the main, generalized in structure. In certain Carboniferous species, however, the prothorax was highly modified, bearing conspicuous projections or spines, which may have had some protective value. The legs of most were of the ordinary walking type, but in one Carboniferous genus (Mischoptera) the fore legs were short and raptorial in form though there are no other indications of predaceous habits. The wings were the most characteristic structures of the Megasecoptera. In most species they were very narrowed basally, and in one family they were arcuate, as in many families of living insects. Two abdominal structures are noteworthy : the very elongate cerci, which surpass in length those of most other insects ; and, in certain families, lateral gill-like proc- esses, resembling those of the Palseodictyoptera. Nothing is known of the immature stages of the Megasecoptera, but



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74 Psyche [June
the presence of the supposed gill-vestiges just mentioned suggests that at least some of them had aquatic nymphs. The Megasecoptera were probably no better fliers than the Palaeodictyoptera, and their long cerci must have handicapped them in their attempts to escape from ene- mies. Perhaps this had something to do with their abrupt disappearance at the close of the Permian, for no sign of them has been found in later strata.
We next come to the insect dinosaurs-the Protodonata. These include the largest insects known, living or extinct. Although all species were large, as insects go, not all were giants, as is usually stated; some had a wing expanse of five inches, which is well within the limits of many living insects. Three very large species have been found, all belonging to the family Meganeuridae. One, from the Carboniferous of France, was about twenty-six inches across the wings; the other two, from the Lower Permian of Kansas andOklahoma, were somewhat larger, with a wing expanse of about thirty inches. The distribution of these species, both in space and time, indicates that the giant meganeurids inhabited an extensive area of the earth for some fifty million years, though the whole order became extinct shortly after the close of the Permian Period. The protodonates resembled dragon-flies in gen- eral appearance, and the earlier forms were probably directly ancestral to the true Odonata. They had large, toothed mandibles and spiny legs, and were undoubtedly predaceous. What they fed on, we can only guess. The contemporary slow moving Palaeodictyoptera and Mega- secoptera, which, because of their wing structure, were unable to hide easily among plants or under rocks, were probably their chief source of food. Protodonate nymphs , are unknown. They were probably aquatic, although Dr. August Krogh has asserted that nymphs of the giant meganeurids could not have breathed through caudal or rectal tracheal gills, as odonate nymphs do, since in order to convey the necessary quantity of oxygen to the head, their trachea would have required a cross-section greater than that of the body itself.
However, passage of oxy-
gen in the tracheae might well have been sufficiently a,ided



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19471 Early Insect Life 75
by muscular movement to make this mechanism practical. At any rate, the adult Protodonata and Odonata are so much alike, I find it difficult to believe that their nymphs were very different.
The insects which we have been considering so far are primitive types which we would expect to find as part of early insect life. The group we are now to discuss is not in this category. For although their wings were of the palseopterous type, the head was modified into a long rostrum, with suctorial mouth-parts. The best preserved specimen (Eugereon) of this group has been found in Upper Permian rocks of Germany, but other representa- tives, also with elongate beaks, have been collected in Carboniferous strata of France, Belgium, and England. Since these insects were at first thought to have been related to the Hemiptera, Handlirsch termed the order the Protohemiptera. The choice of name was unfortu- nate, for, with the discovery of new specimens, it has become increasingly clear that they had nothing to do with the Hemiptera, but are instead closely related to the Palseodictyoptera. The order was obviously a widely dis- tributed one, members having been found in Permo-Car- boniferous strata of both Europe and North America; and specimens from Triassic rocks of Australia show that it persisted into the Mesozoic. The Triassic representa- tives, by the way, are remarkable in that the fore wings had a very large stridulatory area. The Palseozoic Proto- hemiptera had long cerci and well developed prothoracic wing lobes, like those of the Palseodictyoptera. The pres- ence of suctorial mouth-parts raises the question of feed- ing habits. It is obvious from their modified mouth-parts that the Protohemiptera consumed liquid foods ; whether this was plant juice, from such gymnosperms as lycopods, seed-ferns, and horse-tails, or the blood of reptiles and amphibians, is uncertain. But it is most interesting that as far back as the Upper Carboniferous, at least two hun-