Amber tomb of ‘dancing’ wasp and delicate flower also hides a gruesome secret
A tiny flower that blossomed 30 million years ago still lingers today in near-perfect condition, preserved inside an airless amber tomb with only a wee wasp also frozen in place for company.
Finding this insect and bloom suspended close together offers clues about their relationship in the tropical ancient ecosystem that they once inhabited, according to a new study published June 16 in the journal Historical Biology.
The bloom belongs to a previously unknown flower species in an exceptionally rare group, and hidden inside one of its spherical seed pods was a secret stowaway: the developing larva of a minuscule fly, which may have been intended as a future meal for the wasp’s young.
Study author George Poinar Jr., a researcher in the Department of Integrative Biology at Oregon State University’s College of Science in Corvallis, Oregon, described the wasp in 2020.
The insect was also an unknown species, and Poinar dubbed it Hambletonia dominicana; the species name references the Dominican Republic, where the amber was discovered, and the wee parasitic wasp belongs to a group that is known for preying on other insects, Poinar reported in 2020 in the journal Biosis: Biological Systems.
For Poinar, the wasp’s graceful form and the positions of its perfectly preserved legs made it almost appear to be “dancing,” he said in a statement.
Perhaps the wasp wasn’t interested in the flower and simply wandered into the wrong place at the wrong time, ending up encased in sticky resin.
However, another possibility is that the wasp became stuck near the flower because it was visiting the blossom, either to eat its pollen or for a more gruesome reason: to lay an egg on the plant’s inhabited seed pod, so that the wasp hatchling could then burrow inside to devour the fly larva.
When Poinar collected the Dominican amber specimen several years ago, he was “mystified” by its contents, he told Live Science in an email.
“Since I could not understand how these two different specimens could end up together,” Poinar said. “I felt that the only way I could proceed was to identify both organisms and look for biological features that could explain their ‘togetherness.’”
The flower measures just 0.09 inches (2.4 millimeters) long, and the species name Plukenetia minima (from “minimus,” the Latin word for “least”) is a nod to its diminutive size, Poinar wrote in the new study.
It belongs to the flowering plant family Euphorbiaceae, which includes tropical plants such as poinsettias and the rubber tree The oldest Euphorbiaceae fruit fossils date to the latter part of the Cretaceous period (145 million to 66 million years ago), another team of researchers reported in the February issue of the International Journal of Plant Sciences.
However, fossil evidence of this group is rare and only one other fossil flower is known, from sedimentary deposits in western Tennessee, Poinar wrote.
P. minima had a long stalk and no petals, but was instead topped by four seed pods, one of which held a single fly larva with a “smooth body” and a pair of tiny antennae.
Based on its body size and shape, it appears to be a larva of a gall gnat, a type of small fly in the Diptera order that attacks flowering plants of all kinds, according to the study.
The amber-preserved wasp may therefore have been attracted to the infested plant “in order to deposit an egg that, after hatching, would have parasitised the gall gnat larva,” Poinar wrote.
But instead, flowing resin ensured that larva, wasp and flower all met the same sticky fate, and were preserved together for tens of millions of years to come.
The delicate bodies of small insects and the structures of tiny plants and flowers rarely fossilize, and most have been lost to time. In this case, the amber inhabitants are rare examples of fossils that retained substantial structural details from when they were alive, providing a unique glimpse of their tropical “microhabitat” from the distant past, Poinar wrote in the study.
“The degree of preservation is so much more complete in amber than in other fossils,” Poinar said. “The amber fossils are life-like, which makes the characters easy to describe. It is like they just entered the amber.”