What Bugged the Dinosaurs?

Fig.1. Cimex lectularius, the terrible bed bug.

"Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
The frumious Bandersnatch! "
Jabberwocky, by Lewis Carroll (1832-1898)

Insects entombed in amber were noted since antiquity; however a first naturalistic research and binomial description occurred only in 1779 by Marcus Elieser Bloch (1723-1799), just one year after Linne´s death. Bolch studied copal, a fossil tree resin younger then classic amber, ranging only some million years in age.
Most of early palaeoentmological work dealing with fossils in amber or fine-grained sediments was not carried out by professional entomologists, but by geologists, botanist and insect collectors, considering the incredible diversity of insects (925.000 named species until now) an exceptional self-confidence, resulting however often in a chaotic taxonomy, incorrect descriptions or depictions. But it would be unfair to minimize the efforts of these pioneers, they acted in best intent.
With the beginning of the 20th century this general approach became replaced by specific research of professional entomologists.

Insects are the most successful multicellular animal group on earth today, and there is no reason to assume that in the geological past the situation was different.
Amber so provides us with an unique window in this past, and show the diversity and various behaviour that insects evolved over time.

Diverse recent organisms make a living by nourishing on blood, most notable the vampire bats and leeches, even some human cultures, especially the Masai of Kenia, have discovered fresh blood as valuable food, but non of these groups is so successful in the habit to suck blood as the insects.
Not all insects that bites need blood to feed, some species use blood only in certain periods of their development, for example as protein source for egg production. Some insects are generalists and will attack fishes, amphibians, reptiles, birds and mammals, other are more specialized and prefer single groups or species.
Insects, despite the common claim, don't bite, but saw or cut out our skin. Mosquitoes then punctuate direct a blood vessel, and suck the blood (capillary feeders). Other insects group, like blackflies, biting midges, sand flies, and horseflies lacerate the blood vessels, and lick the blood that accumulates in the wound (pool-feeders).

The insect record is a very old one; fossils are known since the Carboniferous, however in part very fragmentary, most modern groups are known only with the beginning of the Triassic or Cretaceous, and groups that today feed on blood are known mostly since the Cretaceous.
Bloodsucking insects from include different insects groups, however mainly dominated by the "flies" (Diptera) as snipe flies (Rhagionidae), athericid flies (Athericidae), blackflies (Simuliidae), biting midges (Ceratopogonids), Sand flies (Phlebotominae) and horse flies (Tabanidae).
Fleas (Siphonaptera) and lice (Phthiraptera) are the second largest group of obligatory blood feeders, and finally also some bugs (Heteroptera) have evolved a taste for blood.
Even if there is no direct evidence that the ancestors of these insects feed on dinosaurs, like a palae-flea fossilised on a dinosaur, the contemporaneity of these groups and dinosaurs makes it highly probable that the insects did benefit from the availability of such large blood packs.
The skin of the dinosaurs comprised various dimensions and patterns of scales or even scutes, some showed scales perfectly fitting each to another, on others the scales or tubercle were embedded in the thin skin, and finally some dinosaurs were also covered by bristles, filaments, proto-feathers and feathers. These various categories however do not exclude each and another, some species possessed body parts covered by classic reptilian epidermis and some parts were covered by feathers.
In every case the skin did not provided an impenetrable wall against all sorts of bloodsucking organisms.

Mosquitoes (Culicidae) are the most familiar group of the blood sucking insect, however they are quite rare in the fossil record and only single specimens confirm their presence during the Cretaceous. Most of the recent forms are opportunists, they will attack whatever host is available, even if preferring mammals and birds, but from 5 genera it is known that they feed also on lizards.

Biting midges (Ceratopogonidae) resemble a tiny version of mosquitoes, in most cases their attack is not noted, only after their dinner a fastidious itchiness remembers their presence. This group is commonly found in Cretaceous amber, and it is probable that they in the past also targeted dinosaurs. Ceratopogonids today are pool feeders, they will attack all sorts of vertebrates and concentrate their effort on regions of a body were blood vessels are easily approachable, like the area surrounding the eye or joints, were scales are smaller or the skin thinner.

Blackflies (Simuliidae) are tiny insects like the biting midges; however they are capable to travel for long periods and can come in gigantic swarms. It seems that large quantities of these insects are capable to weakening and even kill large mammals by the suffered loss of blood.
Fossil remains occur during the Jurassic and Cretaceous in Europe, Australia, Asia, and North America, modern forms are not known to feed on reptiles, but they feed on birds.

Sand flies (Phlebotominae) are probably one of the earliest groups of flies in which some species evolved the ability to suck blood; they switched from nibbling on plants to obtain liquids to use animal wounds during the Jurassic and evolved in the Cretaceous the habit to actively gain blood. Most of them today are general feeders, feeding on all sorts of vertebrates, some species however prefer lizards and snakes, and have no problem to reach the soft skin under the overlapping scales.

Horse-flies and deer-flies of the family Tabanidae were widespread throughout the Cretaceous and today are strong, persistent flies, and appropriately feared as blood pool-feeders on both warm- and cold-blooded animals.
Their "bite" is nasty and often where the insect feed a painful wheal develops. Today at least four species of horseflies are known to prey on crocodiles and anacondas in the Amazon, also turtles and birds can not escape their attacks.

Fleas (Siphonaptera) and lice (Phthiraptera) today thrive under the protection of hairs and feathers on both mammals and birds, and it seems reasonable to assume that they or similar organisms could also accept feathered dinosaurs as habitat. In case of reptilian skinned dinosaurs, it is interesting to note that modern fleas try to avoid reptiles as hosts, probably by the lack of shelter offered by the scales.

Fleas and flea-like insects, like Strashila, have in fact been described from Mesozoic sediments. A robust beak indicated that Strashila may have sucked blood, and claws on the well developed hind legs might have been used to grip feathers or bristles.

Fig.2. Another bizarre, apparently ectoparasitic mecopteroid, Strashila incredibilis, reconstructed from the part and counterpart specimen from the Late Jurassic of eastern Siberia. The huge hind legs were probably used for grasping onto its host. The lobes on the abdomen are an enigma; body length 6 mm (GRIMALDI & ENGEL 2005).

Another Mesozoic flea-like insect (it is tentatively attributed to Mecoptera, group related to true fleas), is the large-bodied Saurophthirus longipes, the prolonged proboscis, extended claws, and long legs have been considered modifications for parasitic behaviour on pterosaur wings or to grasp the border of large dinosaur scales.

Lice are highly specific parasites of mammals and birds, and are placed in two categories, the biting (Mallophaga) and sucking (Anoplura) types. The latter all feed on mammalian blood, while the biting forms, thought to be more "primitive" and older then the sucking forms, feed on feathers, hair, skin and blood.
Fossil lice are rare, from the Cretaceous of Transbaikalia the species Saurodectes is known, a contemporary of dinosaurs and pterosaurs, and possibly feeding on them.

Fig.3. A large Mesozoic louse? Saurodectes vrsanskyi, photo and reconstruction, from the Early Cretaceous of Baissa, Siberia (ca. 140 Ma); body length 17 mm (GRIMALDI & ENGEL 2005).

Blood sucking insects represent today a particular danger for men and animals.
Despite the possibility to become exsanguinated by billions and billions of tiny flies, the true danger coming from insects is that they are acting as highly movable vectors of pathogens. Research on blood sucking insects conserved in amber showed that many of them carry microbes, resembling modern pathogens that cause Leishmania and Malaria, and also small invertebrates and parasites like nematodes.
It is not clear how much these insects contributed to the ecology of dinosaurs, but surely, as today, they played an important role.

Bibliography:

BREHM, A.E. (1892): Insekten, Tausendfüßer und Spinnen. Brehms Tierleben Bd.9. Ernst Ludwig Taschenberg.
GRIMALDI, D. A. & ENGEL, M. S. (2005): Evolution of the Insects. Cambridge University Press: 755
POINAR, G. & POINAR, R. (2007): What Bugged the Dinosaurs? Insects, Disease, and Death in the Cretaceous. Princeton University Press: 296
RASNITSYN, A.P. & QUICKE, D.L.J. (eds.) (2002): History of insects. Kluwer Academic Press: 517