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Oldest insect camouflage behaviour revealed by fossils
Rare insect fossils preserved in amber have revealed the camouflaging technique of carrying debris dates back more than 100 million years.
Some insects have developed a remarkable method of evading predators and fooling prey - cloaking themselves in organic debris such as sand, soil, leaves and other dead insects.
It is a masterful method of camouflage, using the environment to hide their bodies and match their habitats.
This behaviour has been documented in crabs, spiders, snails and insects.
An international team has uncovered the earliest evidence of this technique by studying insects preserved in amber.
The scientists found that insects used debris for camouflage during the Cretaceous Period, between 145 and 66 million years ago.
According to Edmund Jarzembowski, a Scientific Associate at the Museum and one of the researchers involved, the study demonstrates the oldest evidence of widespread camouflaging behaviour with debris.
A reconstruction of how an owlfly larva could have looked in the middle of the Cretaceous Period © Bo Wang
He says, 'These were exciting specimens to work on, because you don't often see specialised terrestrial larvae in the fossil record - it it is more common to see fossilised flying adults.
'Debris-carrying is also a fascinating and complex behaviour. It requires the ability to recognise, collect and carry materials that will suitably camouflage the insect. It is a very sophisticated behaviour, and I was delighted to see so much new material documenting it.'
A wolf in sheep's clothing
Little is known about the early evolution of camouflaging behaviour.
To date, only one specimen from the Mesozoic Era (252 to 66 million years ago) has been found to show such behaviour. Most scientific knowledge about the behaviour has come from studies of much younger fossilised insects.
For this study, published in the journal Science Advances, researchers examined more than 300,000 insects, preserved in amber since the age of the dinosaurs.
Nearly all the specimens were found in Burmese amber, from northern Myanmar. This high quality, clear amber is now easier to access and is proving a treasure trove for Cretaceous fossil finds.
Only 35 insects showed evidence of debris carrying: assassin bugs and the larvae of lacewings and owlflies.
One of the lacewing larvae was preserved carrying the exoskeletons of other insects, including small barklice.
Other specimens were found covered in a variety of debris such as sand grains and plant, wood and bark fibres.
These specimens reveal that the behaviour is a phenomenon that was well-established by the middle of the Cretaceous Period, more than 100 million years ago.
A preserved spider was found preying on a nymph larva that was not camouflaged © Bo Wang
Jarzembowski says, 'Modern-day larvae carry discarded prey to make them look and smell like the creatures they want to eat.
'They become like wolves in sheep's clothing - able to deceive other unsuspecting insects’.
'Our findings show that some prehistoric insects employed exactly the same technique.'
Predator against prey
Although carrying extra weight means the insects sacrifice mobility, the increased success when stalking prey must outweigh these hindrances.
Jarzembowski thinks it is most likely threats from predators such as spiders, lizards, birds and other insects that caused the evolution of complex debris-carrying techniques.
Among the fossils examined in the study was that of a spider, found preying on a nymph larva that was not wearing camouflage.
It is early, direct evidence of a predator-prey relationship.
Jarzembowski says, 'There is still a lot that we don't know about camouflaging behaviour. It may be a case of evolution in action - the insects that got bits of plant and other debris stuck to them survived longer than those that didn't.
'But it is also important to note that being camouflaged helped these insects catch their own prey - a doubly effective strategy.'
Independent evolution
Remarkably, the study also found that different species independently evolved the ability to camouflage themselves.
A reconstruction of how a lacewing larva could have looked in the middle of the Cretaceous Period © Bo Wang
The species developed different physical features that allowed them to effectively gather debris - techniques that surviving species still use.
Some insects used their jaws or legs to scoop up organic fibres. Others had long, bristle-like structures on their abdomens that swept up and fastened debris from the environment around them.
It is common in modern species of camouflaging insects to use their hind legs as shovels, to gather and load material on to their bodies.
Jarzembowski says, 'There is so much more work to be done in this field. New discoveries of insects preserved in amber are being made all the time, and I anticipate there are thousands of new species we have yet to discover.
'Many of them are likely to reveal new and fascinating behaviours, body shapes and survival techniques.'
