Cretaceous Amber Reveals Insect Relationships Scientists in Spain analyzed six key samples of amber, containing extinct insects, to try to learn more about the ants that lived in the Cretaceous period. “Amber inclusions are representative of possible interactions between different organisms shaping the environment,” explained Dr Jose de la Fuente of the Institute for Game and Wildlife Research, Spain, lead author of the article in Frontiers in Ecology and Evolution. The six pieces he and colleague, Agustín Estrada-Peña, studied span several key periods of time. Four pieces from Myamar's Hukawng Valley are from the Cretaceous Period, (99 million years ago). One piece of Baltic amber from Poland is from the Eocene Period, (40–55 million years ago). Another piece from the Dominican Republic is from the Oligocene Period (23–34 million years ago). Each contains ants alongside other organisms. This phenomenon is very rare, and referred to as "syninclusion" by palaeontologists. Ants were the focus precisely because they are, and probably always have been, so ecologically central by aerating soil, dispersing seeds, predating or being predated upon, and locked into relationships with hundreds of other species. The trouble with amber taphonomy (the study of how organisms end up preserved) is that proximity doesn’t guarantee interaction. A spider and an ant might share a piece of resin because one was hunting the other, or because both landed in the same patch of tree sap within minutes of each other through sheer bad luck. De la Fuente and Estrada-Peña tried to distinguish these scenarios by measuring the distances between organisms and cross referencing with published evidence of known ecological relationships. The earliest ants are known as Stem ants. Although they didn’t leave modern descendants, Hell ants are suspected to have evolved from them. These two, along with Crown ants, which all ants alive today evolved from, were found in the amber samples. Three of their six cases involved ants near mites, and these are perhaps the most compelling. Hitching a ride on a larger animal (phoresy) is well documented in living mites. Some modern mites that are associated with ants are mutualists (cleaning their hosts in exchange for transport), while others are parasites. In Case 1 (Baltic amber), a Crown ant was found with two mites of the family Glycyphagidae at 1.9 and 3.7 millimetres distance, alongside a wasp, an oak flower and some moss. The Glycyphagidae found in Case 1 appear consistent with the phoretic interpretation, possibly riding the ant to reach new food sources. Whether the relationship was beneficial or damaging to the ant is another matter; without micro-CT imaging to look for attachment structures on the mites, the paper stops short of a firm conclusion. In Case 4 (Burmese amber), a Stem ant lay about 4.4 mm from a mite showing a sclerotised body, consistent with a mobile, phoretic life stage. “The proposed ant-mite interactions in Case 4 may reflect two possible scenarios.” de la Fuente says. “First, a commensal specialized temporal relationship where mites attach to ants for free ride dispersal to new habitats. Second, a parasitism when mites feed on the ant host during transport.” Case 6 contains a Stem ant with its body curved backward, mandibles pressed against what looks like a worm or perhaps a neuropteran larva. The ant appears to be of the genus Gerontoformica (or close to it), which is part of the early eusocial lineages that preceded a diversification of ants in the later Cretaceous. Its body posture, with mandibles apparently in contact with substrate, suggests active foraging or scavenging behavior. A nearby spider, about 4 mm in compact body length, likely belonged to the Gnaphosidae family. This family of ground dwelling hunting spiders whose members today sometimes mimic ants to avoid being eaten by other predators, or to infiltrate ant colonies. It is unclear whether this long dead spider was doing something similar; using proximity to the ant as camouflage rather than fleeing from it. The Hell ant in Case 3 adds another layer entirely. Hell ants (Haidomyrmecinae) are among the strangest extinct insects we know of: their forward-projecting scythe-like mandibles bear no resemblance to any living ant, and they were probably specialized predators. This one was preserved alongside a land snail, a millipede, and two poorly preserved insects. A Hell ant eating a snail seems possible. Ants today prey on mollusks in some circumstances. But the distances between the organisms in Case 3 are larger, and de la Fuente’s team treats these as likely coincidences rather than evidence of interaction. That caution is probably right. “The closest ant syninclusions are more likely to reflect behavior and interactions between these organisms,” de la Fuente says, but the researchers are explicit that distance alone cannot determine what was happening. Amber distorts as it fossilizes, compressing three dimensional relationships into something harder to read. What looks like intimate proximity might reflect different moments in time, and what looks like coincidental clustering might have been deliberate. “The identification and morphological characterization of fossil ants in amber with other inclusions of insects provides a snapshot of life on Earth millions of years ago,” de la Fuente says. “To improve the analysis of interactions between different organisms in fossil amber inclusions, future research should use advanced imaging techniques,” said de la Fuente. “Nevertheless, these results provide evidence of insect behavior and ecological habits.” Micro-CT scanning can render the spatial relationships between organisms in three dimensions, potentially revealing whether mites have the sclerotised attachment structures they’d need to cling to a moving ant. Z-stack imaging can build up layered composite pictures of partially obscured inclusions. These techniques are already transforming what’s possible with amber paleontology. A 2024 study on termites used CT scanning to confirm that ancient termite colonies preserved in amber reflected genuine social group behavior, rather than accidental clustering.