Fossilised mosquito meal

Blood from the last meal consumed by a mosquito 46 million years ago has been identified inside a fossilised mosquito found in Montana.

Writing in PNAS, Dale Greenwalt and his colleagues at Washington DC's Carnegie Institution, initially used X-rays to examine the remains of a female mosquito preserved in a layer of fossilised mud that would have rested on the floor of a pond in what is now north-western Montana.

Consistent with the mosquito's engorged appearance, the X-rays showed a strong signal corresponding to iron, which would be in keeping with the insect having binged on a blood meal not long before it presumably drowned in the pond.

Next, the team cleaned away the surface of the fossil to remove overlying material, and then used a technique called "time of flight secondary ion mass spectrometry" - ToF-SIMS - to probe the chemical composition of the insect itself.

In this system, charged particles are fired at a surface where they knock out molecules that can be sucked up and identified by the analyser.

Stable molecules called porphyrin rings, of which haemoglobin is one, were detected, giving a signature closely matching pig blood tested as a control.

This suggests that blood has been preserved within then fossil, and that some of the chemicals sucked up 46 million years ago by the now-fossilised female mosquito are still preserved within its remains today.

Ironically, this paper, which comes 20 years after the Hollywood blockbuster Jurassic Park in which dinosaur DNA was recovered from mosquitoes preserved in amber, is actually the first such description of a blood-engorged fossilised mosquito!