A fossil wasp from about 99 million years ago had an unusual apparatus at the tip of its abdomen: three overlapping flaps, including a spiny, bristled lower flap. Researchers think the structure may have temporarily grasped a host while the female laid an egg. The comparison to a Venus flytrap is vivid, but this was an insect structure—not a plant trap—and its function is inferred from fossils rather than observed behavior.
What was found in the amber?
In a 2025 study, Qiong Wu, Lars Vilhelmsen, and colleagues described 16 adult female wasps preserved in Kachin amber from Myanmar. The specimens came from Noije Bum hill in the Hukawng Valley of northern Myanmar. The study reports the amber’s age as 98.79 ± 0.62 million years, commonly rounded to about 99 million years. The specimens are held in Capital Normal University’s insect fossil collection in Beijing. The study in BMC Biology named the species †Sirenobethylus charybdis and proposed a new genus and family, †Sirenobethylus and †Sirenobethylidae, within the wasp superfamily Chrysidoidea.
How did the wasp’s “Venus flytrap” rear end work?
The key feature was at the end of the abdomen, where three flaps overlapped. The broad lower flap carried spines and long bristles. In different fossils, that flap is preserved in different positions relative to the other two, offering clues to how the parts could move.
The team examined the fossils with optical microscopy and photography, and used micro-CT scanning on a paratype. Comparing the preserved anatomy supported the interpretation that the flaps formed a grasping apparatus. The authors wrote that “the rounded abdominal apparatus, combined with the setae along the edges, is reminiscent of a Venus flytrap.” The bristles may have served as sensory trigger hairs, but that is also an interpretation, not something directly preserved as behavior.
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What did the wasp use it for?
The researchers’ leading hypothesis is that a female used the apparatus to restrain a host temporarily while laying an egg. They infer that the wasp was probably a koinobiont parasitoid: its offspring would develop using a host that was not killed immediately. The amber preserves no wasp in the act of catching or holding prey, so the proposed function remains an inference from anatomy.
The host species is unknown. The paper discusses possible mobile insects, including hoppers or small flying insects, but does not identify a prey animal. The fossils do not establish that the wasp caught any particular species.
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What is known—and what remains inferred?
| Question | What the study establishes |
|---|---|
| What was the structure? | Three abdominal flaps, with spines and long bristles on the broad lower flap; fossils preserve it in differing positions. |
| How old and where were the fossils? | Kachin amber from Noije Bum hill in Myanmar’s Hukawng Valley; 98.79 ± 0.62 million years, as reported by Wu et al. in 2025. |
| What was its function? | Temporary host restraint during egg-laying is the researchers’ best-supported interpretation, not directly observed behavior. |
| What was the host? | Unknown; no host species is identified. |
| How many wasps were described? | 16 adult female specimens; this is the study’s specimen count, not an estimate of the ancient population. |
Why does this fossil matter to wasp evolution?
Using a morphological analysis of 57 characters across fossil and living groups, the authors placed †Sirenobethylus as a distinct lineage near the base of Chrysidoidea. Their interpretation adds evidence that parasitoid strategies in this group were more varied in the mid-Cretaceous than among its currently known members. It does not demonstrate that wasps and modern Venus flytraps share a specific evolutionary mechanism.
The authors concluded that “the new fossils suggest that Chrysidoidea displayed a wider range of parasitoid strategies in the mid-Cretaceous than they do today.” That evolutionary conclusion is based on comparisons of preserved anatomy and inferred relationships, not a record of the wasp’s actions.
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Why call it a “Venus flytrap wasp”?
The nickname captures the resemblance of the rounded, bristled abdominal apparatus to the edges of a Venus flytrap. It should not be taken literally: this was a wasp with an unusual anatomical structure, not an insect carrying a plant trap. In an Associated Press interview, co-author Lars Vilhelmsen described the structure as “a small bear trap attached to the end of it.” Both comparisons help convey its shape; neither proves exactly how it functioned.
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