You always knew midges were ferocious – but did they kill biggest beasties of all?

DINOSAURS may have been killed off by biting insects rather than a cataclysmic meteor impact, a new theory claims.

Disease spread by ancient mosquitoes, mites, ticks and perhaps even the ancestors of the Scottish midge, was probably what finished off the reptiles, say scientists.

By changing the nature of plant life on Earth, insects could have made it harder for dinosaurs to survive.

Bees and other pollinators helped promote the rapid spread of flowering plants unsuited to the traditional diet of vegetarian dinosaurs. As the plant-eaters declined, so would their predators.

The theory helps explain why dinosaurs took so long to die off, according to husband and wife team George and Roberta Poinar.

According to the most widely accepted explanation, the dinosaurs were wiped out by an asteroid or comet that smashed into the Earth off the coast of Mexico 65 million years ago.

Another theory is that they were driven to extinction by massive volcanic eruptions in India which led to extreme climate change.

The time at which the dinosaurs disappeared, between the Cretaceous and Tertiary periods, is known as the K-T Boundary.

But George Poinar, a professor of zoology at Oregon State University in Corvallis, points out that they did not vanish immediately. Their extinction was drawn out over hundreds of thousands or even millions of years.

An impact scenario should have led to an abrupt extinction, and volcano-induced climate change would probably also have wiped them out relatively quickly.

On the other hand, emerging diseases spread by biting insects, combined with the spread of flowering plants, and competition with insects for plant resources was "perfectly compatible" with a lengthy process of extinction, said Prof Poinar.

Insects date back as far as the Carboniferous period, around 300 million years ago. During the later part of the dinosaurs' reign, insect numbers and species exploded. Mosquitoes evolved in the early Cretaceous. The oldest example known, from Burma, was trapped in amber 100 million years ago. Prof Poinar and his wife have carried out a study of plants and creatures preserved in amber, the fossilised resin that is used for ornaments and jewellery.

They outline their dinosaur-extinction theory in a book published by Princeton University Press, What Bugged The Dinosaurs? Insects, Disease And Death In The Cretaceous.

Prof Poinar said: "During the late Cretaceous period, the associations between insects, microbes and disease transmission were just emerging.

"We found in the gut of one biting insect preserved in amber from that era, the pathogen that causes leishmania – a serious disease today, one that can infect reptiles and humans. In another we discovered organisms that cause malaria, a type that infects birds and lizards today.

"In dinosaur faeces, we found nematodes, trematodes and even protozoa that could have caused dysentery and other abdominal disturbances. The infective stages of these parasites are carried by filth-visiting insects."

He said that during this period, the world was covered with warm-temperate to tropical areas, swarming with blood-sucking insects. The infections they carried would have caused epidemics that slowly wore down dinosaur populations.

"Smaller and separated populations of dinosaurs could have been repeatedly wiped out, just as when bird malaria was introduced to Hawaii, it killed off many of the honeycreepers," Prof Poinar added.