Blackflies

A mountain stream coursed around and over boulders and tree roots through a glen in the forest. Clinging to the surface of the rocks were clusters of small, upright blackfly larvae equipped with a pair of strainers used to sieve out passing food items rom the current. Unlike the robust aduts that aggressively searched for blood, these immatures quietly waited for miniscule food items to pass by and be netted. When the blackfly larvae were satiated and eager to make the transformation into the air, they formed pupae attached to the rocks in the stream. A few days later, an adutt blackfly emerged rom each pupa. They didn 't mind experiencing a few splashes of water before they became airborne. Masses of these tiny ferocious insects emerged at the same time and formed a swarm that flew off in search of their first blood meal.

A group of hadrosaurs browsed among the reeds bordering a pond. One of the more inquisitive members detected floating white flowers on a mat of water lilies and ventured into the water to dine on the treat. Thick, sticky mud oozed between large toes as the big female shifted ponderous weight from leg to leg. Upon reaching the tasty plants she bent forward to the water's surface and began stripping off the flowers and lush, succulent leaves of this delicacy until only the tasty bulbs half buried in the mud were left. After some wary glances around the edges of the pond, the duckbill submerged a massive head and began prodding the bottom with broad sensitive lips. Mayfly and water-beetle larvae frantically scurried away from the disturbance while caddis flies pulled into their cases and remained motionless. At this moment, a famished horde of blackflies landed on the back of the dinosaur and started to penetrate the thin layer of skin with their sharp mandibles. The unfortunate beast reacted to the vicious stabs by jerking her head out of the water and attempting to brush the pests away. Any vertebrate could tolerate some suffering from these insects, but not that generated when so many attacked at once. By now the voracious insects were excising miniscule portions of flesh and lapping up the exposed blood. Snorting wildly, the frantic hadrosaur lay down in the water, but the pain persisted and the blackflies remained attached. Rising and shaking vigorously, the harried animal splashed out of the pond and fled toward the forest, stumbling over some boulders and bruising both knees as she attempted to dislodge the tormentors. Risking a broken leg in this hasty flight, she finally found refuge among some tall ferns. The blackflies, if undisturbed, would have continued feeding, and if their numbers were thick, could have drained her body of blood.

Did millions upon millions of blackflies soar over Cretaceous fens and fern grottos, clogging the nasal passages of feeding dinosaurs? Would their appearance cause dinosaurs to stampede, tripping over rocks, breaking legs, or plunging off cliffs in a frantic rush to escape the torturers? Were toxic substances in insect saliva causing allergic reactions and blood poisoning? Could masses of these noxious flies cover a dinosaur's skin and remove so much blood that it would expire from exsanguination? All of the above are known to occur today when blackflies attack grazing bovines on the plains of western Canada.204 205 These insects are capable of swarming over the prairie for miles searching for cattle. The most dramatic result of these forays is exsanguina-tion—when hundreds at a time settle on a victim and drain the blood over the course of a few days. Even if some survive the initial attack, many eventually succumb from broken bones, starvation, and infections. Such a scene is not limited to Canada; a few decades ago, blackflies undertook massive migrations along the Danube in eastern Europe that resulted in the death of thousands of cattle, sheep, goats, and pigs.205 This may well have happened to dinosaurs.

Blackflies were certainly present in the Cretaceous since records of them extend back to the Jurassic. Fossil remains occur in Europe, Australia, Asia, and North America.205-208 It would be helpful to establish what Cretaceous species dined on since there is no evidence that this group is attracted to cold-blooded animals today. A single study reports females clustering around the eyes of a turtle, but not feeding.209 In fact, blackflies are the only large group of hematophagous insects that have not been observed feeding on reptiles.

However, they do attack birds and mammals. While there were Cretaceous birds and mammals, it seems unlikely that these bloodsuckers would have ignored the dinosaurs because they were an obvious unlimited source of protein. Furthermore, if dinosaurs and birds are as closely related as some believe, then dinosaurs might well have been among their original hosts.

It has been suggested that their sanguinary pursuits started with pterosaurs, a group that may have been warm blooded because they needed heat for their flight muscles.205 Did pterosaurs, some of which were sparrow sized, pre-adapt blackflies to eventually partake the life's fluid of birds and mammals? Then again, whether dinosaurs were warm- or cold-blooded or some condition in between may not have mattered to blackflies. If some lineages specialized just on dinosaurs, they probably disappeared along with their hosts, leaving behind those that favored feeding on birds and mammals.

One of the blackflies preying on hadrosaurs or their kin could have been carrying a malarial protozoan (Leucocytozoon) in the salivary glands, which was then introduced into the bloodstream of the victim. In the following weeks, these microorganisms would multiply in the tissues and blood cells of the host, establishing a chronic infection that could weaken the animal's immune system, lower its reproductive potential, and even cause death. Today, a similar disease (leucocytozoonosis) is often fatal to ducks, geese, chickens, and especially turkeys.204

Cretaceous blackflies also may have been transporting filarial nematodes. These wiggling parasites would enter the blood vessels and be transported into the internal organs. After accumulat ing in certain tissues, the nematodes would mate, deposit their eggs, and the young microfilaria would then wait to be picked up and transported to a new host animal by yet another blackfly. This cycle is much like one that currently infects ducks.173

A particularly grim blackfly-transmitted nematode similar to the one that causes river blindness in humans feasibly may have been infective to dinosaurs. Some 17 million people in tropical Africa and South America are afflicted with this blinding disease, which is caused when larval nematodes spread into the eyes of the victim, resulting in visual impairment and eventually total loss of sight.204 A dinosaur with compromised vision not only had difficulty finding food, but also was easy prey for predators.

While studying the nematodes causing river blindness in West Africa, our team of scientists found that an effective way to trap black fly vectors was to wait along the side of a stream and catch them as they settled on our skin. We were highly motivated to act quickly, since if they bit us, within seconds the microscopic nematodes the flies were carrying would enter our blood-stream—and no one wanted to risk losing their sight. Apparently we were not fast enough, and one of the group eventually developed telltale nodules that indicated the presence of mating adult worms, whose progeny is responsible for vision loss. Treatment at that time consisted of two drugs, one for the juvenile nema-todes migrating through the tissues and another for the adults in the skin lumps. Since both of these remedies had side effects, our colleague had the cysts surgically removed in Europe. Recently an ivermectin-based drug has provided a much more effective and safer type of treatment, and hopefully will aid in the extermination of this tragic disease.

With the exception of Antarctica, blackflies are presently distributed throughout the globe. Their larvae require running water for survival, so they are limited to locations with streams and rivers. However, the adults are capable of flying hundreds of miles (assisted by the wind) from their breeding sites in search of blood, and thus their range would have been fairly extensive in the Cretaceous.

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