ENTOMOLOGY \ RESOURCES FOR THE PUBLIC \ Fossil flies in amber

Fossil Flies in Amber
by Dr. Brian V. Brown, Assistant Curator of Entomology
From Terra magazine, May/June 1998, vol. 35(3): 8-9.

Photograph of fossil amber.For an entomologist, amber is a window into the past. Inside the hardened, fossilized tree resin, insects are frequently preserved in stunning detail, and sometimes in all the various stages of their life cycles. These ancient specimens can not only reveal the life histories of long-dead species but give us clues to when our modern fauna first appeared and when distinctive features of today's insect lineages first evolved.

The Entomology Section of the Natural History Museum recently obtained a collection of 122 pieces of amber, from the Yantarni mine in Kaliningrad, at the south end of Russia's Baltic Sea coast. This amber is approximately 35 to 40 million years old and thus was formed around the end of the Eocene epoch and the beginning of the Oligocene. Although the insects it contains lived long after the Age of Dinosaurs, which ended 65 million years ago, the Baltic amber period was still a time when life forms looked very different than they do today.

The amber itself was produced as a secretion of trees, but the actual tree species are still being debated. Scientists have traditionally believed the source of Baltic amber to be a pine because the amber contains many pinelike fossils, including wood, needles, and cones. But analysis of its spectral qualities has revealed that this amber closely resembles resins produced by more primitive conifers related to the monkey puzzle tree and others of the genus Araucaria. Like the ginkgos and the palmlike cycads, which lived in Europe during the Baltic amber period but now have a much more reduced distribution, Araucaria trees today are native only to the Southern Hemisphere.

Photograph of phorid fly from the Eocene.Illustration of phorid fly from the Eocene.


A pair of phorid flies from the Eocene (approximately 40 million years ago) preserved in Baltic amber; the drawing, by Jesse Cantley, is based on the photo he took.

Apparently these small insects- the male is about 2 millimeters long- were flying as a mating pair and, when they landed on the sticky resin, tried to scramble away from each other. The female, at left, has a distinctive cockroachlike appearance, with small eyes, reduced wings, and a rounded "limuloid" body. These flies are being described as a new genus and species by Dr. Brown.

Our new amber collection is interesting to me because each piece contains one or more phorids, the tiny flies that I study. Members of this family, which is found worldwide, have a wide range of life styles, from scavenging, predation, and parasitism to plant eating. Their abundant populations and small size- the largest phorids are just under a quarter of an inch long- guaranteed that many would be caught in the sticky resin flowing from amber-producing trees.

The Baltic amber period was one of the most interesting times in phorid evolution. Unlike older Cretaceous amber, where most of the phorids present are barely recognizable as such, the Baltic amber contains modern groups along with their relatively primitive ancestors. There are some surprises as well, including the earliest known specimens of a truly bizarre group of phorids (the subfamily Aenigmatiinae) in which the females look something like cockroaches; one couple was in the act of mating when captured by the amber resin (see illustrations below). The early relatives of other modern phorids with cockroachlike (or "limuloid") females are present in the Baltic amber. But the fossilized females have well-developed wings, while their closest living relatives are wingless. Today's limuloid phorids live in the nests of ants or termites, potential hosts whose fossils are common in Baltic amber.

Electron micrograph of a modern limuloid female phorid fly.

A modern limuloid female phorid fly (genus Epicnemis) from Thailand. Note the smooth, rounded body form, reduced eyes, and complete lack of wings (males of this genus have normal-sized eyes and well-developed wings). Scanning electron micrograph by Brian V. Brown.

Other better known phorids are preserved in the new collection. There are several specimens of Anevrina, a genus whose species feed on carrion in the burrows of mammals. There are a number of Triphleba phorids, whose larvae are known to feed on buried plant and animal material. Finally, there is a species of Godavaria, a genus now found only in the Himalayan region of southeast Asia, thousands of miles from the Baltic Sea.

In the new collection, there is at least one genus of phorids new to science as well as many undescribed species. These novelties are not surprising, because most species of insects are not expected to survive unchanged for more than a few million years. Describing these new forms from specimens in amber is always a challenge, as the crucial structures that need to be examined often seem to be just out of sight, or hidden by a pair of inconveniently bent legs. Patience on the entomologist's part, as well as an abundance of specimens upon which to base descriptions, is the key to increasing our knowledge of these fossils from the dim past.