Treasures in Gemstones: Previously Unknown Wasps Found in Prehistoric Amber
By Leslie Mertz, Ph.D.
Most of the mined amber in the world winds up as gemstones in earrings and necklaces, but sometimes it has a greater purpose: It makes its way to entomologists who find beautifully preserved prehistoric insects inside. A case in point is the new report of never-before-seen wasps found in Baltic amber dating back at least 40 million years. “I was pretty excited when I found them,” says Roger Burks, assistant specialist in the Department of Entomology at the University of California, Riverside, who co-authored a report about his discovery, published in December 2019 in the journal Insect Systematics and Diversity.
Burks came across the wasps while helping Germany’s Stuttgart State Museum of Natural History go through amber samples, which are chunks of fossilized tree sap, dating back to the Eocene epoch (about 34–55 million years ago). The museum had already narrowed down about 600 of the samples to a group of small wasps in the superfamily Chalcidoidea, but they needed a specialist to do more detailed identifications. Burks is one of only a handful of people in the world with that expertise, and fortunately he had time in his schedule to make the trip to Germany.
Even though the insects were just 2–3 millimeters (mm) long and encased in rock-hard sap, his knowledge of extinct and extant (still-existing) wasps allowed him to quickly sort the samples into their proper families and subfamilies. Then he came across something different. He spotted one that had the distinctive features of wasps in the subfamily Chrysolampinae, which was unusual because no members of that subfamily had ever been identified from the fossil record. With a closer examination, he ultimately found four specimens that had Chrysolampinae’s telltale features, including the shape of the forewing veins, antennal segments, and clypeus (a face sclerite or “face plate” just above the mouth).
Chrysolampine wasps are an especially interesting group of insects, because they have an unusual life history, Burks says. The Chrysolampine wasps are parasitoids, a way of life common to many wasps and other insects. In a typical parasitoid, including most members of the Chalcidoidea superfamily, the female lays her eggs on or in a caterpillar or other host organism, and, when the eggs hatch, the larvae start eating the host, eventually killing it. The Chrysolampines do things differently. Instead of laying the eggs in or on the host, the female lays them on a plant “vaguely near the host,” Burks explains. When the eggs hatch, the tiny newborn larvae (called first instars) have to set out to find a host themselves, a formidable task considering that the first instars are only about 0.2 mm long, and they have a very soft body that could easily dry out or be snapped up by any number of predators.
Despite the high mortality rate that likely accompanies that lifestyle, Burks notes that no member of the subfamily has ever evolved away from it. “It’s counterintuitive; they’re still successful. This suggests that there’s a very interesting local optimum happening here in the evolution of this lineage, and it’s pretty interesting to me that we now know this has been happening for 40 million years,” he says.
Since first identifying the four specimens, Burks has been able to pinpoint their genus as Brachyelatus, which has extant members in Australia and Europe, and he determined them to be a new species. “I named the species after my mother Martha Shadle, so it is Brachyelatus marthae,” he says. He felt it a fitting tribute for the woman who, throughout his teen years, drove him 20 miles every weekend from their rural Arkansas home to the nearest library. This allowed him to continue educating himself once he left formal schooling in 7th grade to help with the family firewood business. He describes his mother as “not an incredible fan of insects,” so he kept the details about the wasp’s bizarre parasitizing behavior to himself when he told her about her namesake. Overall, he says she’s happy about the honor, and he’s looking forward to sending her a copy of the article.
In the meantime, Burks continues to investigate fossils in the Baltic amber samples. “There are a few different Chalcidoids that we have, and we’re not quite sure what family some of them are, or if there should be new families or subfamilies,” he says. “It’s a real question right now about what’s the best approach for these fossils, because we don’t want to make a bunch of split-off families that don’t have any context, but at the same time we don’t want to place them in an existing family and be wrong about it.” He is also inspecting amber from northern France dating from the early Eocene (48–55 million years ago), and from Burma dating from the Cretaceous period about 99 million years ago.
Thinking about the discovery of Brachyelatus marthae and all of his work with amber-encased prehistoric insects, Burks says it has opened his eyes to the wonders of nature and evolution. “It helps stretch my imagination and makes me aware of the amazing diversity of biological organisms that I might never have thought possible,” he says, adding “And you get the idea that quite a few interesting fossils may be sitting in a jewelry box in someone’s home.”
Insect Systematics and Diversity
Leslie Mertz, Ph.D., teaches summer field-biology courses, writes about science, and runs an educational insect-identification website, www.knowyourinsects.org. She resides in northern Michigan.