the pioneer entomology by William Kirby and William Spcnce. "Were a naturalist to announce to the world," they write, "the discovery of an animal which first existed in the Fossil Insects form of a serpent; which then pene- trated into the earth, and weaving a Frank M. Carpenter shroud of pure silk of the finest texture, contracted itself within this covering into a body without external mouth or limbs, and resembling, more than any- Written in the rocks of Colorado, thing else, an Egyptian mummy; and Kansas, Oklahoma, and many other which, lastly after remaining in this places is the story of insects in the ages state without food and without mo- before man appeared on earth. tion . . . should at the end of that pe- The insects were trapped, caught in riod burst its silken cerements, struggle mud or sticky resin, and thereby left a through its earthly covering and start permanent record—as did dinosaur, into day a winged bird—what think mollusk, and plants—that broadens you would be the sensation excited by our knowledge of their evolution. this strange piece of intelligence ? After About 12,000 species of fossil insects the first doubts of 'its truth were dis- have been described. Countless thou- pelled, what astonishment would suc- sands of specimens have been collected. ceed! Amongst the learned, what sur- Fossil insects are not found in as mises!—what investigations! Even the many deposits or localities as most most torpid would flock to the sight of other invertebrates. Like other organ- such a prodigy." isms, insects are preserved as fossils by a sequence of events that results in EDWIN WAY TEALE is a past presi- their burial in a suitable medium. Im- dent of the New York Entomological mediate burial is necessary to preserve Society and the author of numerous the whole insect ; otherwise the body books on insects, including Grassroot parts soften and fall apart, and only Jungles, The Boys' Book of Insects, the wings remain. The wings decom- Near Horizons, The Golden Throng, pose more slowly and therefore can be and North With the Spring. His hooks preserved under less favorable condi- have appeared in British, Spanish, tions. That is the reason why many French, Swedish, Finnish, and Braille specimens of fossil insects consist of editions. Near Horizons was awarded wings alone. When conditions were the John Burroughs Medal for distin- good for preserving insects, large num- guished nature writing. In ig4g, Mr. bers of fossils usually occur. Teale edited a one-volume omnibus of An example of such abundance is the writings of F abre, entitled The provided by the Tertiary shales at Flo- Insect World of J. Henri Fabre. rissant, Colo., which have yielded up- wards of 60,000 specimens. The shale originated about 40 million years ago in a shallow lake, extending into sev- eral narrow valleys and rimmed by granitic hills. Several neighboring vol- canoes frequently erupted and scat- tered ashes and debris over a wide area. Whatever insects were flying or were being blown over the lake at those .^^ times were forced into the water by the falling ashes and were promptly buried. Stenomema canadense, a common mayfly. Fossil insects have been found at 14 Fossil Insects nearly 150 localities in various parts of and Ural River in the east. The north- the world. About nine-tenths of the ern and western borders are uncertain specimens have been collected at 12 of because those regions are covered by these deposits. The remainder has com.e the ocean. At any rate, the local ac- from less productive rocks. Some of the cumulation of the amber along the latter are important because of their coast of East Prussia is the result of the geological position, however. One of washing out of the flooded forest. In- them is the Commentry shales of cen- sects and other small invertebrates, tral France. These were deposited by which were caught in the resin on the a deep fresh-water lake, which existed tree trunks, arc preserved in great de- during the Upper Carboniferous pe- tail and perfection. At least 150,000 riod some 250 million years ago. About insects have been found in the amber. 1,500 specimicns have been found in The earliest geological record of the the shales. They are well preserved and insects is still uncertain. Fragments of are almost the oldest insects known. small arthropods, which have been re- Another deposit, notable for the covered in a Devonian chert in Scot- abundance of fossils as well as their land, have been determined by some ages, is the Elmo limestone in eastern entomologists as Collembola (spring- Kansas. The rock, fine-grained and tails), but the identity will remain nearly white, w^as deposited by a shal- doubtful until more is known about low fresh-water lake inhabited by them. The oldest unquestionable in- aquatic insects, crustaceans, and small sects have been found in rocks of early king crabs. A collector who carefully Upper Carboniferous age, about 250 breaks the limestone, after it has been million years ago. Only three of these dug up and dried, may get as many as fossils are known—one each from 50 good insects a day. Most of the fos- Czechoslovakia, Germany, and Penn- sils arc strikingly well preserved. Some sylvania—and each consists of a single show even the coloration and minute wing. Whatever else may be inferred hairs on the wings. About 10,000 speci- from the specimens, it is certain that mens so far have been collected there. insects with fully developed wings ex- A similar but more extensive lime- isted then. stone formation was discovered in 1940 Insects are much more abundantly in northeastern Oklahoma. It origi- represented in the later Upper Carbon- nated in a shallow, saline lake, barren iferous rocks than in the earlier ones, of life except for algae and bivalve so that we have at least a working crustaceans (Conchostraca). Most of knowledge of the insect fauna of the the insects preserved there were pre- time. Six orders of insects have been sumably carried to the lake by floods. recognized, all but one of them extinct. The lithographic limestone of Ba- The most interesting was the Palaeo- varia, famous for such fossil vertebrates dictyoptera, which were of medium as the flying reptiles and the earliest size and resembled mayflies. Since birds, is not nearly so important for its some of the Palaeodictyoptera were insects. Several thousand specimicns more generalized than any of the other have been found there, but fev/er than winged insects known, the group as a one-tenth of them are well preserved. whole is usually considered to be the The richest of all deposits is the Bal- ancestral stock from which all other tic amber from Germany. The mate- winged insects have been evolved. As rial is itself the fossil resin from an far as we know, all species of the order extinct pine tree {Pinites succinijera). had a pair of membranous lobes on the The Amber Pine Forest existed for first thoracic segment. The lobes ap- several million years during the early pear to be homologous with the func- Tertiary period, and extended from tional wings of the other two thoracic about the site of Bornholm and Rügen segments and are regarded as indicat- in the south to that of the White Sea ing the steps by which functional wings i6 Yearbook of Agriculture 1952 arose. Unfortunately nothing is known Geological Ages of Existing Orders of about the immature stages of the Pa- Insects laeodictyoptera. The order reached its Na7ne of order Earliest geological record maximum development in the Carbon- CoUcmbola Devonian [?]. iferous period but persisted through Entotrophi Middle Tertiary, Thysanura Jurassic. the Permian period. Odonata Lower Permian. The most spectacular insects of the Ephemeroptera . . . Lower Permian. Carboniferous and Permian were the Plecoptera Upper Permian. Protodonata. They resembled dragon- Orthoptera Triassic. Orthoptera Upper Garbonif- fíies. Their chewing mouth parts were (Blattidae). erous. powerful, and their legs, like those of Isoptera Lower Tertiary. true dragonflies, were covered with Dermaptera Jurassic. strong spines. They were undoubtedly Embioptera Lower Tertiary. Corrodentia Lower Permian. prcdaceous, catching their victims in Mallophaga [No fossils known.] flight and devouring them w^hile rest- Hemiptera Lower Permian. ing on tree ferns or other ancient Anoplura Quarternary. plants. All of the Protodonata were Thysanoptcra .... Upper Permian. Mccoptera Lower Permian. large and some were veritable giants, Neuroptcra Lower Permian. having a wing expanse of 30 inches and Trichoptera Jurassic. a body length of 15 inches. Specimens Diptera Jurassic. of such large species have been found Siphonaptera Lower Tertiary. Lepidoptera Lower Tertiary. in rocks in France, Kansas, and Okla- Coleóptera Upper Permian. homa. Since birds and other flying Strepsiptera Lower Tertiary. vertebrates did not exist at that time, Hymenoptcra .... Jurassic. these huge insects presumably ruled the air. Their nymphs have not been sects. Although the several extinct found, but they were probably aquatic orders which arose in the Carbonifer- and like those of true dragonflies or ous still existed, several living orders damselflies. besides the roaches were represented. The only living order or group of Along with the giant dragonflies WTTC families of insects known to have ex- minute barklice, only one-eighth of an isted in Carboniferous time is the Blat- inch across the wings. Altogether, the tidae, or cockroaches. Their remains lower Permian insect fauna was very make up a high percentage of insects of diverse—more so, in fact, than any that period, but that is probably due other insect fauna known. There was partly to the favorable conditions pre- about equal representation of the ex- vailing in the Carboniferous swamps tinct orders of the Carboniferous and that produced the deposits. Some for- relatively specialized existing orders. mations of that period, such as the Also adding to this diversity were sev- coal beds of Pennsylvania, have yielded eral other extinct orders, known only no insects except roaches. The average fromx Permian strata. One of them, the size of the Carboniferous roaches was Protelytroptera, included beetle-like in- somew^hat greater than that of living sects, having well-developed elytra, but species, but none of the fossil forms ex- they were closely related to the roaches ceeds in size certain living species of and had no affinities with the Coleóp- the Tropics. The difference between tera. The living orders that appeared the ancient roaches, existing some 250 in early Permian time include such million years ago, and those of today is types as the Odonata (dragonflies), exceedingly slight, involving chiefly Ephemeroptera (mayflies), Corroden- position of wing veins. tia (barklice), Hemiptera (bugs), By the beginning of the Permian pe- Neuroptera (lacewings), and Mecop- riod, about 50 million years after the tera (scorpionflies). The lacewings and appearance of the first insects, a scorpionflies are especially noteworthy marked change had taken place in in- because the living species have com- Fossil Insects píete metamorphosis. Coleóptera and Plecoptcra arc first found in late Per- mian strata, but they probably existed earlier in the period. With the beginning of the Mesozoic era, the insect fauna changed even more markedly. In fact, the contrast between the archaic fauna of the Per- mian and the relatively modern one of the Triassic is as great as that between the faunas of the Triassic and the Re- cent periods. None of the extinct orders remained after the beginning of the Mesozoic. but a few living families oc- cur in Triassic strata. Among the nota- Golden-eye lacewing. ble insects of that period w^ere certain Australian species related to the Or- thoptcra, which had a large stridula- tory apparatus on the wing. This con- stitutes the earliest record of sound production in the insects. Because at the time these insects lived there were no birds or other vertebrates that pro- duce the ordinary animal sounds of for- ests or woodlands, it is quite possible that these stridulating insects and their relatives were the noisiest creatures then in existence. The Jurassic insect fauna was much Plathemis lydia, a dragonfly. like that of the Triassic except that more existing families occur. In fact dragonflies, and true bugs. The insects the appearance of this fauna is so mod- in the Baltic amber, which is now re- ern that if we had a collection of garded as of early Tertiary age, are Jurassic species pinned in the usual especially important in enabling accu- way, it would not look very different rate comparisons with living genera from our present-day collections, ex- and species. Studies of families of cept that there would probably be no amber insects have shown that the flower insects, such as the bees and amount of evolution that has taken syrphid flies. This is a great contrast place since the early Tertiary has var- to the condition of the vertebrate fauna ied for different families. The Baltic of the time, which included the dino- amber ant fauna, for example, includes saurs, flying reptiles, and toothed birds. 43 genera, of which 24, or 55 percent, By the beginning of the next period, still exist, whereas all but one of the the Cretaceous, the flowering plants genera of bees in the amber are extinct. had become established and in all In this connection, it is noteworthy that probability the types of insects asso- William Morton Wheeler, who made ciated with these plants promptly fol- an extensive study of the amber ants, lowed. Unfortunately our knowledge found eight species of them which he of the Cretaceous insects is insignifi- could not distinguish from living spe- cant because of the lack of adequate cies. Furthermore, he also found that specimens. the social habits of the amber ants were Early Tertiary strata have yielded a about as highly organized as those of higher percentage of living genera than the living forms, with caste differen- the Jurassic, especially of flies, beetles, tiation, polymorphic v/orkcrs, and even i8 Yearbook of Agriculture 1952 Table of Geologic Periods Approximc fe time (in millions of years) Era Period Duration of Since begin- period ning ojperiod Cenozoic (age of mammals and fQuatcrnary. I I man) \Tertiary . . . 69 70 {Cretaceous. 50 120 Jurassic. . . . 35 155 Triassic. . . . 35 I go Permian 25 215 Carboniferous^ j PP ^ • 35 250 50 300 Paleozoic (age of invertebrates and Devonian primitive vertebrates) 50 350 Silurian 40 390 Ordovician 90 480 ^Cambrian 70 550 the association with plant-lice. Since vestigations. Although this is still a this was fully 50 million years ago, be- highly controversial subject, we have fore the time when most existing fam- enough evidence at hand, derived ilies of mammals were evolved, it is from these three sources, to indicate apparent that the social organization the main steps in insect evolution. of ants is a much older one than ours. There is, however, no fossil evidence Although Tertiary insects do not bearing on the question of insect ori- contribute so much to our understand- gin; the oldest insects known show no ing of insect evolution as the older fos- transition to other arthropods. On the silsj they have given information about other hand, morphological and embry- changes in geographical distribution of ological studies carried out mainly the genera and families since the early since 1935 ^^LYO pointed to the prob- Tertiary. Many genera and families able origin of the insects from some which have been found in the Baltic terrestrial arthropod, related to the ex- amber are now entirely absent from isting Symphyla. The time of that ori- Europe, and some arc known to occur gin is pure conjecture, but judging only on such distant land masses as from the fossil record we can only con- Australia and South America. The clude it was at least as far back as the same is true of Tertiary insects of other Lower Carboniferous (Mississippian). parts of the world. The Florissant Morphological studies of existing in- shales (middle Tertiary) in Colorado sects prove that the first true insects have yielded several species of lace- were wingless (Apterygota), like the wings of the family Osmylidae, a group Thysanura (silverfish) and Entotrophi, now absent from North America. Hun- combining the generalized characteris- dreds of instances of this sort can be tics of both of these groups. cited. The significance of such changes The development of wânged insects in distribution is not clear and will not (Pterygota) was the first great evolu- be until more evidence has been ac- tionary step within the insect line. The cumulated and correlated with the fos- origin of wings is by no means clear; sil record of other groups of animals they probably were dc^velopcd from and plants. lateral flaps, like those on the first tho- A detailed study of the geological racic segment of the Palaeodictyoptera. history of the insects, which I have only These primitive flying insects, termed sketched, yields evidence of certain the Palaeoptera and exemplified by the progressive changes in structure and Odonata, Ephcmeroptera, and several developme-nt which confirm conclu- extinct orders, were unable to flex their sions on insect evolution reached by wings over the abdomen at rest. morphological and embryological in- The second main evolutionary Fossil Insects 19 change was the development of an the main steps in insect evolution articulation that made it possible for took place before the end of the Car- the wings to be held over the abdomen boniferous period, about 250 million when the insect was not in flight. All years ago. Nothing nearly so important living Pterygota except the Odonata has happened to the insects since then. and Ephemer optera belong in this Another contribution that fossil in- category, which is termed the Neop- sects have made to our understanding tera. The acquisition of this wing-flex- of the evolution of the group pertains ing mechanism was an important to the progressive increase in the rel- change, for it enabled the insects, in ative numbers of species having com- adult as well as the immature stages, plete metamorphosis in the geological to hide in debris or under stones or logs. periods since the lower Permian. Start- The first neopterous types had a simple ing from the beginning of the Permian, or direct type of postembryonic de- during which only about 10 percent of velopment and are usually termed the the known species had complete meta- hemimetabolous Ncoptcra. morphosis, there has been an increase The third main evolutionary step up to 88 percent at the present time. was the attainment of the more com- The most rapid change ( i o to 40 per- plex type of metamorphosis, with larval cent) seems to have taken place in the and pupal stages, resulting in the holo- interval of the Permian period. Al-- mctabolous Neoptera. though there is a possibility that such a The fossil record of the insects, marked shift in the insect population though incomplete, has given us a gen- did actually take place in that time, the eral idea of the time of occurrence of more probable explanation is that the three events. The existence of two complete metamorphosis arose further orders of insects (Mecoptera and Neu- back in the geologic time than the roptera) with complete metamorphosis lower Permian, and that the change in lower Permian rocks can only mean w^as more gradual. that this step was attained at least by Those are two examples of the way late Upper Carboniferous time. Simi- in which the study of fossils has con- larly, the presence of species with wing- tributed to our understanding of insect flexing abilities in the early Upper Car- evolution. There is every indication boniferous shows that the hemime- that the insects have been as numerous tabolous Neoptera arose in the Lower on earth as they are now for at least Carboniferous. Unfortunately, since no the time since the Jurassic period, insects have been found in strata older about 150 million years; and also that than those of the Upper Carboniferous the insect fauna of our time is but a period, we have no actual record of the small part of the total parade of insect existence of Palaeoptera before these life that has lived on the earth during Neoptera ; nor, for that matter, is there the past 250 million years. It is not sur- any Paleozoic record of the Aptery- prising, therefore, that our understand- gota. Because all evidence derived from ing of insect evolution depends to a other sources indicates the primitive large extent on a knowledge of this nature of these two categories, how- extinct population. ever, we can infer that the Palaeoptera preceded the Neoptera, and therefore FRANK M. CARPENTER is professor that they existed in the early part of of entomology, Alexander Agassiz pro- the Lower Carboniferous. Similarly, fessor of zoology, and curator of fossil wc can infer that the Apterygota, insects in the Museum of Comparative which must have preceded them, arose Zoology at Harvard University. He still earlier in the Lower Carbonifer- joined the staff of Harvard in igss ous or, more likely, in the Devonian. and has done research on fossil insects, The conclusion to be drawn from the insect evolution^ and the taxonomy of record, at any rate, is that all three of Mecoptera and Neuroptera.