Harrow and Hillingdon Geological Society

Fossil Insects of the Bembridge Marls

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Fossil Insects of the Bembridge Marls on the Isle of Wight

Dr Andrew Ross

Natural History Museum

This talk described the work undertaken by Dr Ross and a team of 35 people to study a 19th century collection of fossilised insects from mainly the Eocene / Oligocene. The majority of these specimens were unstudied and therefore not classified. The INTAS project provided £100,000 for the research, which is in collaboration with three Russian institutes and other European scientists from France, Poland, Germany, Spain etc.

In the 1870s Joseph Smith discovered insects in the marl beds around Bembridge on the north coast of the Isle of Wight. These marls, which are from the tertiary period are limey muds found on the coast in a region extending from Gurnard Edge to Forland and including Burntwood West, Bembridge, Westcliff Bay and Burntwood East. At the base of the marls is the Bembridge limestone which is about a metre thick and 33 million years old.

The NHM collection is comprised of 500 specimens collected by Smith in 1877 and 1883. In 1898 Brodie purchased a further 2,000 and Hooley added 1,500 in 1924. Many of these specimens are incomplete and interpretation has been difficult and time consuming. There are 165 different species including a praying mantis. Today in UK there are 25 orders of insect.

We were then shown slides of the following:
Plecoptera - Stoneflies order associated with fast flowing streams
Dermaptera - Earwig - soil
Mantodea - Praying Mantis
Ephemeroptera - Mayflies - fresh water lakes
Mecoptera - Scorpion flies
Neuroptera - Lacewings - feed on aphids
Blattodea Cockroaches
Psocoptera - Bark lice - eat algae
Thysanoptera -Thrips - these are about 1mm in size and therefore very small but not the smallest insect
Lepidoptera - Butterflies and moths - these are rare in water deposits as the scales trap air and hence they tend to float and are either eaten or destroyed.
Orthoptera - Locusts, grasshoppers, crickets, mole crickets (very rare) mainly underground
Isoptera -Termites - these are very primitive and today are restricted to Australia
Odonata - Damselflies, dragonflies - most of these specimens are incomplete

The specimens are also indicative of the climate of the time which was tropical.

Hemiptera - Bugs, water boatmen, plant hoppers, cicadas, aphids
Coleoptera - Beetles, ground beetles (not often well preserved), ladybirds are rare in the fossil record, weevils are the most common of the beetles, rove beetles and dung beetles
Hymenoptera - Ants - most abundant in the bed social wasps, digger wasps which are closely related to bees. Ichneumon wasps, fig wasps which are highly specialised only the ♀ have wings, the presence of fig trees also indicate a tropical climate.
Diptera – Flies, craneflies, Marchflies, mosquitoes, fungus gnats, soldier flies, horse flies, the aquatic larvae as fossils tolerate calcareous water and survive dessication.

Conclusions: Everything has either been washed in or flown over and drowned in the water. It is a depositional environment, hypersaline and as a salt lake insects could not tolerate the chemistry. The terrestrial ecology was reed marsh, springs, meadows and forest and therefore suitable sites for living and breeding. Crickets, grasshoppers = dry areas – meadows, weaver ants – forests. Its age was generally early Oligocene.

These specimens were very different to those found in Baltic amber. The climate was equable subtropical and a much smaller temperature range between the seasons. A very interesting picture is emerging from this research.

This was essentially an illustrated talk with a wonderful collection of slides in which each fossil was displayed alongside its modern day counterpart. A vast amount of work has been done and the speaker said a lot remained to do. It also gave an insight into how fossils can help unravel climatic conditions of the period. It was a fascinating lecture living up to our usual very high standard.

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