The Case for Entomophagy among Dinosaurs

A particularly large beetle was rolling a dung ball away from one of many fecal piles dotting the over-grazed plain when it was suddenly pounced upon and gobbled down by a young or-nithomimid. After consuming a few additional unlucky adults, the dinosaur started to dig around the perimeter of the drying excrement, searching for juicy dung beetle larvae, but they were buried too deeply and he left to try his luck elsewhere.

Further away at the perimeter of the dense forest, an immature pachycephalosaur was nibbling on cycad leaves when a sudden movement caught his eye. A large cockroach that had been resting in the dried leaves at the base of the thick stem had been exposed when the plant was disturbed. The youngster bent down and snapped up the delicacy, which represented a concentrated package of protein and fat needed by the growing animal. Deciding to probe around for more, the small juvenile pushed his head further into the fallen leaves at the base of the plant. As some earwigs crawled away from their now-divulged hiding place, they too were gobbled down. The dinosaur then proceeded to scrape away the overlying plant debris, uncovering the top layer of soil and thereby revealing some ground beetles that were added to the meal. When satisfied that no more insects were available at that spot, he then turned his attention back to the cycad leaves, since these and other plants would constitute the main part of this omnivore's diet.

Another diminutive dinosaur was inspecting a babbling brook for prey by systematically turning over partially submerged rocks and targeting mayfly and stonefly larvae. The disturbance caused eddies that suspended caddis and Dobson fly larvae, which had been resting underneath the stones. A hurried attempt was made to snatch them up before the current carried them downstream. Finally some of the blackfly larvae that crowded around the edge of the rocks just beneath the rushing water were pulled from their holdfasts and swallowed. Aquatic insects were plentiful and it was not difficult obtaining a good meal from the clear waters.

In all probability, almost every dinosaur, even those considered vegetarians, were in actuality omnivores at some point in their lives, certainly when they were in the rapid growth stages and possibly also during periods of egg production. You may question how we arrived at that conclusion, but even today characterizing an animal as an herbivore, omnivore, or carnivore is an almost impossible task, so we assume the same held true for dinosaurs. Few vertebrates are truly one or the other. For example, mammals begin their lives dependent on a food source rich in protein, mother's milk. Fruit- and nectar-eating birds feed bugs to their young, and because many insectivorous birds take fruits and seeds as well, most birds would be considered omnivores.133 So both mammals and birds start life eating animal proteins, and although some go on to become herbivores as adults, overall they could be classified as omnivores. Since some paleontologists consider birds living dinosaurs, the principle of behavioral fixity dictates that omnivory was common among dinosaurs as well.302 Also, scientists are discovering that a large number of animals traditionally considered herbivores or carnivores will cross over when given the opportunity, especially during periods of plenty or scarcity of one type of food.

Some animals consume the most unexpected things. For instance, there are flesh-eating deer, hippos, chimpanzees, and hamsters, and fruit-eating wolves, bears, badgers, and mongooses. The list becomes even more extensive when you look at who in the animal world ingests insects at some time or other. In fact a much easier way of looking at it would be to identify only those that don't! After all, eating arthropods makes a lot of sense. They are the most abundant animals around and represent a readily available source of protein. The same range in omnivory seen in present-day animals would probably also apply to dinosaurs. Probably most herbivorous dinosaurs, and certainly all of the carnivores, actively searched for and consumed insects during their growing years. Insects could be regarded as the ideal convenience food of the Cretaceous.

Vertebrates aren't the only ones whose eating preferences don't fit nicely into a definite category. In almost all insect families, there is some crossover from herbivory to carnivory or vice versa. Sometimes one type of feeding behavior is characteristic of the larvae and another of the adults. For example, mosquito larvae ingest plant debris and microorganisms, while adult females are mostly bloodsuckers. Almost all bloodsucking flies also imbibe sugar from plants or nectar-producing insects for long-term survival. Grasshoppers and their kin often stop to partake of dead or dying insects, and cockroaches are well known for including both animal and plant matter in their meals. Even primitive springtails add nematodes to their diet of pollen and spores. Many plant bugs will lunch on other invertebrates encountered on leaves. And larvae of many aquatic insects, like caddis flies, subsist on both plant and animal matter they scrounge from the bottoms of ponds and streams.

Passive Feeding

As herbivorous dinosaurs munched away on ferns, cy-cads, and conifers, they passively consumed hundreds, even thousands, of insects in their food (color plates 5B, 12C). Could the passive ingestion of insects by megaherbivores be regarded as an important food additive? Initially, we assume that a sauropod weighing 80 tons and eating thousands of pounds of plants per day was hardly affected by say, a few pounds or so of accidentally consumed bugs. But consider that aside from the obvious proteins, fats, and fiber, insects contain a number of vitamins and minerals that might be regarded as beneficial.134 Proteins, vitamins, minerals, or even chitin in incidentally swallowed insects may possibly have been required for the maintenance of vital intestinal symbionts of some dinosaurs. Lack of insects in their diets might have meant impeded digestion, poor health, or a greater susceptibility to disease. Perhaps there were components in insects required by dinosaurs for hormonal production.

On the other hand, we know that many insects sequester toxins from plants today, and in the Cretaceous, they may have killed or sickened dinosaurs that unknowingly ate them. The effect of passive ingestion of insects on dinosaurs is purely speculative at this point, but remember that any action, no mater how seemingly insignificant, is not without some consequences. Even if the passive consumption of insects by dinosaurs had no discernable effects on the eaters, it certainly had one on the eaten, possibly even reducing populations of some phytophagous insects.

Although we have, in the United States, stringently controlled guidelines for food purity, humans unknowingly ingest numerous insects in prepared products. A spaghetti dinner, for example, could contain over seven hundred bits and pieces of arthropod parts and still be considered acceptable under USDA standards. This is still quite a bit less than mankind consumes in other parts of the world and considerably less than the intake by herbivores past and present.

Active Searching

There can be little doubt that insects represented an important component of the food chain in the Cretaceous. As primary consumers, insects certainly served as an energy source for many small animals, which in turn were consumed by larger animals, and so on. Insects provided an easily available source of much-needed protein for precocial dinosaur hatchlings that received no parental feeding.

We believe that most, if not all, dinosaur young fed on insects. How long this dependency on them remained cannot be determined. Many large present-day mammals, including humans, consume insects as an occasional or even regular part of their diet. Some of these animals can hardly be considered diminutive, with bears topping out around 800 pounds and pigs at 500-plus pounds. It follows that dinosaurs of similar proportions also incorporated insects into their diet regardless of whether they were carnivores or herbivores. The importance of insects and other invertebrates in any food web cannot be over emphasized. They are frequently forgotten or dismissed because of their size, but they represent more than half of the biota and without them, much of the food chain would collapse.

Active searching for insects by dinosaurs presumably occurred in multiple habitats. After storms, some probably snapped up stranded leaf beetles and moth larvae that had been defoliating various plants. We can easily imagine scale insects on twigs being lapped up with long, mobile tongues, and dinosaur young might have even relished the sweet exudates produced by these tiny insects, just as children delight in sugary sweets.

During the entire year, adolescents were on constant lookout for large arthropods. Defoliating insects on ferns, conifers, and angiosperms served as a snack, but hefty wingless walking sticks, jumbo cockroaches, and giant preying mantids provided better meals. Certainly the most abundant of these were cockroaches (color plate 6D) that occurred under rocks, in debris, around piles of dung, on and under dead animals, and scrambling over tree trunks. Their associations with dead animals and dung also made them important vectors of dinosaur parasites such as protozoans and stomach worms.135 Various types of larger orthopterans were also available for consumption and undoubtedly provided excellent meals. These included crickets, katydids, monkey grasshoppers, elcanids, wetas, and mountain crickets or haglids. The latter feed high in the trees at night and might present a challenge to all but arboreal predators. One of the few remaining representatives of this family subsists on sta-minate cones of conifers.136 The males sing to locate mates, but in the Cretaceous their love songs may have attracted hungry dinosaurs.

Crickets and grasshoppers (color plates 4A, 4B, 8A) made choice dietary morsels throughout the Cretaceous, either plucked from their feeding places on the foliage of conifers or collected from the surface of ponds when the wind blew them off course. Some of the Cretaceous grasshopper-like elcanids50 probably built up high populations at certain seasons, stripping the leaves from plants (color plate 8A). The chances are good that they formed swarms, just as locusts do today. When populations peaked, their massive hordes were sought out by a variety of dinosaurs, as well as by other vertebrate and invertebrate predators. Searching in the soil for mole crickets and around the bases of tree ferns, cycads, palms, and bamboos for wetas and king crickets presented a more challenging job for insectivorous dinosaurs, but many birds and lizards currently are successful at it. And dinosaurs that were accustomed to opening plant stems could have dined on large, juicy beetle and moth larvae.

Some ornithomimids and even troodons possibly collected aquatic insect larvae by turning over rocks in the streams or browsing the detritus-littered bottoms of ponds. Selected tidbits like mayfly, stonefly, and dragonfly nymphs, especially when crawling out of their aquatic homes to enter the terrestrial world, made excellent meals. Just as humans collect and eat caddis fly larvae,137 the dinosaurs could have done the same millions of years ago (color plate 7C).

Ponds supplied snacks such as giant water bugs and large water beetles, although even the smaller backswimmers and water boatmen would qualify if enough were collected. Depending on the speed and agility of the individual hunters, dragonflies and damselflies plucked from the tips of reeds or possibly knocked to the ground from the air made a good mouthful. At certain times of the year, large swarms of midges and lake flies (chaoborids)

amassed over lakes and ponds, mating and laying eggs, and within a few days their bodies piled up inches deep along the shores. Even if the dinosaurs had to venture onto the mud flats to scoop them up, the huge numbers of these tiny insects surely made it worth the effort. Along the borders of the marsh grew rushes with leafy galls containing populations of psyllids. These particular rushes might have been selected as food items by adolescent saurichischians after they had relished the tubers and corms of sedges infested with moth and weevil larvae.

While trudging from one feeding site to another, there was always the chance of encountering a large spider or scorpion. These arachnids would have been a delicacy, just as they are in some human societies.137 138 Whether the scorpion's sting discouraged some of the dinosaurs is difficult to say, but extant birds and mammals appear to have no problem eating them.

At certain seasons, many insects aggregate for mating or dispersal and are easily captured. So June beetles periodically swarming around dying gingko trees, stink bugs amassing on conifer foliage, and even pygmy grasshoppers (color plate 7B) congregating within some of the larger tree buttresses were presumably welcomed, perhaps even anticipated, and then devoured en mass by dinosaurs.

The periodic emergences of cicadas certainly attracted the attention of some dinosaurs as the brownish nymphs slowly crawled up tree trunks or flutter-dried their wings after shedding their drab outer coat. The presence of these fairly large insects without a doubt became known to all after they began their deafening screeches. At this time, it is likely that agile dinosaurs plucked them, still shrieking, from the branches. The calories that these insects had accumulated after years of feeding on plant roots provided predators with a good energy source.

Insects that breed relative quickly on plant foliage can build up populations large enough to be utilized as food. Planthoppers comprise one of these groups (color plates 2A, 2B). Normally small, often beautifully colored and curiously shaped, these insects feed on plant juices and together with spittlebugs and leafhoppers presumably added some variety to the diet of small insectivorous dinosaurs.

The sudden appearance of thousands of shimmering specks in the sky has signaled the emergence of millions of winged termites throughout time. Humans in various cultures herald the arrival of these insects, and they certainly attracted the attention of dinosaurs. Termites provide a good meal easily gathered in a short amount of time. My experience with eating termites came when I was working in Burkina Faso on a project funded by the World Health Organization some years ago. A heavy downpour had thundered on the tin roof of our compound for about ten minutes before passing. When I went outdoors to feel the refreshing cool air that followed the storm, I was astonished to find thousands of large, winged termites rising up from what appeared to be every square foot of soil as far as I could see. The cook was already out carrying a pail of water in one hand and enthusiastically grabbing at the fluttering termites with the other. Upon securing one, a quick movement of the wrist plunged the helpless captive into the water. After collecting several hundred, the cook prepared them by stripping the wings from their bodies and throwing the still active creatures into a pan of boiling water. Then everybody in the camp sat around and dipped into the communal pot, pulling the floating limp bodies from the oily water and popping them into their mouths. After contemplating a greasy one in my hand for a while and wondering if their intestinal symbionts formed heat-resistant stages, I decided that I really preferred them fried, but the others obviously relished them.

Fossil evidence confirms that termites existed throughout the Cretaceous (color plate 7A). Those opportunistic feeding binges they afforded dinosaurs when emerging only lasted a few hours and were periodic events, occurring just several times during the year. How did dinosaurs take advantage of these social insects at other times? Many types of troodons probably used their large curved claws to break through the hardened walls of termite mounds. Their narrow snouts made them well suited to enter the damaged mounds and snap up the tender workers. With some additional effort, they might have been able to reach the royal chamber and find the choicest item of all, a large queen so filled with protein-rich eggs that she was unable to move. Of course, the soldier termites were not going to stand by idly while their home was invaded, and they would have rushed to sink their huge mandibles into the lips of the marauders. Those predators that didn't have the strength to break into a termitarium could have simply waited by the openings for the workers to begin their daily tasks and then gobbled them up.

We can assume that dinosaurs also ate ants, which were present at least by the mid-Cretaceous (color plates 6A, 6B, 6C). While their queens are not much larger than workers, they contain a concentrated sac of proteins, and it is plausible they were eaten as they emerged from the old nest or while searching for new nesting sites. Some of the ants back then might have made nests inside living or fallen partially decayed trees. Those dro-maeosaurs that preferred ant eggs, larvae, or pupae only had to destroy the nests to reach the brood. If some Cretaceous ants lived in climates with a relatively long dry period, additional delicacies known as replete workers lurked inside the nest to tantalize the predators. The swollen bodies of these workers served as receptacles of sugary material collected by the foragers. Today, Australian aborigines,139 as well as a host of birds and mammals, spend hours digging up these honey-pot ants from their subterranean homes.

While we as yet have no evidence that Cretaceous ants used this method of storage, aphids and scales were there to produce honeydew. Aside from a few flowers, most sugars likely came from excretions of scale insects and aphids, insect groups that were abundant throughout the Cretaceous. Many of these small sugar factories turn plant juices into delectable metabolic compounds that are a preferred food of many extant ants. And they are so important to the ant colony that when new queens leave their homes in search of fresh adobes, they will often take along one of the sugar-secreting scale insects to insure a supply for their progeny. So did dinosaurs have a taste for sweets, like birds and lizards do today,56 and if so, would they have enjoyed a little sugar along with their protein meal of insects?

The raiding of ant nests wasn't without inherent problems since Cretaceous worker ants were equipped with large powerful stingers that probably released painful toxins, and they never hesitated to use them against anything threatening their homes, including dinosaurs. So marauders would have had to pause in their quest from time to time to wipe them away. Perhaps those irritations acted as a deterrent and prompted some to quickly decide that putting up with such insults wasn't worth the benefits of a few juicy ant larvae. But if a few stings did not matter that much, insectivorous dinosaurs with a preference for ants probably just stood on a mound and consumed the defenders that rushed from the nest and swarmed onto their feet and legs. In cases where the ants lived in trees, the workers were undoubtedly snatched directly from the leaves, branches, and bark.

What about bees? When we think of bees, we think of social bees that store the honey we find so delectable. However, the great majority of bee species are solitary, like Melittosphex, and only store a mixture of pollen and nectar for their larvae, much too little to interest most vertebrates. While records of Cretaceous honey-producing social bees have not yet been confirmed, primitive stingless social bees similar to those found in the tropics today may have appeared in the Late Cretaceous when an-giosperms were more prominent. If these little bees were around, their comings and goings very likely were noticed, and dinosaurs may have even followed workers that were collecting pollen back to their nests or detected the small bees entering and leaving the tiny wax-coated holes on the trunks of dead standing trees or in the ground. While the nests located at the tops of the trees were out of reach, those at the base of the trunk or in the soil were available for raiding. Some canny individuals possibly detected the faint hum that these bees produce and only had to dig to find the honey-filled cells in ground nests.

Upon uncovering the nurseries, dinosaurs would have been rewarded with a variety of edible treats, including large wax cells containing pollen, nectar, and honey, as well as smaller ones with eggs, larvae, and pupae. This mixture of wax, sugary material, and insects was probably quickly gobbled up. While these small bees lacked functional stingers, they still swarmed out of their nests to attack the intruders. Their main means of defense was their mandibles, and although even smaller than a housefly, they crawled over the faces of the looters, entering their ear openings, nostrils, and mouths. Aside from biting into these membranous areas, some of the workers could have smeared a wax-like greenish material over the eyes of the assailants, obscuring their vision and causing them to stop and wipe their eyes. Since their liquid, dark brown honey is often stored together with older supplies that have become fermented and sticky,137 the raiding dinosaurs must have emitted a strong stench when they finished their meal.

Aside from looking for ant, termite, or bee nests in old trunks, dinosaurs certainly ripped open rotting logs to collect the large juicy larvae of lucanid, oedomerid and longhorn beetles, just as we see crows use their beaks to break open logs and dine on such resources today. And while they were examining exposed logs, some of the smaller beetle larvae, like those of the click beetles, tumbling flower beetles (color plate 5D), passalid beetles, and flat-headed borers undoubtedly were used as a food resource.

All dinosaurs would have eaten insects at one point or another during their development, especially when they were growing. We can assume that those dinosaurs that were basically herbivores as adults passively consumed many insects along with their plant food, while the insectivores and even some larger carnivores persistently fed on them throughout their lives.

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