Rather than changing their body shape and color, some animal species carry around objects to make themselves blend into the background. Insects caught in amber prove that this is not a recent development, with specimens going back 130 million years.
The benefits of camouflage are so large that it is widespread throughout the animal kingdom. However, only a few animals are able to adjust their color when moving between different environments. So temporary shielding can be very handy, as MacBeth found out to his cost. Many creatures have taken to carrying bits of leaf litter or other debris around with them.
Like most behavioral traits, however, this can seldom be observed in the fossil record, so little is known about when it originated. However, the trapping of insects in amber is useful for more than the plot of science fiction films, since it preserves anything they are carrying along with the insect itself. A team led by Dr Bo Wang of the Nanjing Institute of Geology undertook the enormous operation of examining 300,000 insect specimens that met their demise in tree sap.
Prior to Wang's work, only a single insect, a 105-million-year-old green lacewing from Spain, had been found dating back more than 50 million years. With publication in Science Advances, Wang has changed that dramatically, reporting 35 new specimens that showed clear evidence of camouflaging behavior, many dating back to the mid-Cretaceous. Twelve of the specimens, all found in Burma, are discussed in the paper.
Myrmeleontoid larvae from Mid-Cretaceous Burmese and French ambers
The behavior was clearly widespread in the Age of Dinosaurs, with insects found carrying things in what is now France and Lebanon as well. The insects were also more creative than just grabbing a nearby leaf. Wang and his co-authors list “insect exoskeletons, sand grains, soil dust, leaf trichomes of gleicheniacean ferns, wood fibers, and other vegetal debris,” among the items carried. Moreover, the diversity of ways in which insects held onto their disguises led the authors to conclude that the behavior appeared multiple times and evolved convergently.
“Both the Burmese and Spanish fossils exhibit unique debris-carrying modifications, including shapes and arrangements that have not been reported in other chrysopoid taxa,” the paper reports.
In one case, an insect is thought to have been carrying the remains of its own prey after consuming the innards, possibly not only protecting against predators, but making itself less conspicuous to further prey.
Mid-Cretaceous Burmese Myrmeleontoid larvae in amber and an artist's impression of how they might have appeared in life. Wang et al Science Advances.
Besides demonstrating the ancient roots of this behavior, the authors point out that their work offers insight into the ecology of the Cretaceous. For example, several insects were carrying bits of ferns known to be early colonizers after fires. “This supports a relationship between fire events and the high production of plant resins and highlights the importance of wildfires in Mid-Cretaceous [pre-flowering plant] ecosystems as well,” the authors write.