Sphecomyrma fossil ants (Jered, USA)

Hello antweb team,

I am a huge fan of the ants and the antweb team. I have learned so much about ants from you guys, and have also taken away important life lessons from many of your eloquent responses.

My question is.. can you please tell me some things about Spechomyrma and other ant ancestors? What makes Sphecomyrma an ant and not a wasp? Also, what extant lineages of wasps are most closely related to ants? Lastly, do either ants or their wasp ancestors have free will?

Thanks so much!

Dear Jered,

Thank you for contacting AntBlog and sending in a question about ant fossils. We have asked a colleague, Dr. John LaPolla, who is currently working on some fossil ants to address your question and here is what he had to say:

"Great question about what makes Sphecomyrma an ant or not an ant. This is something ant experts have variously debated. There are a few morphological features of ants that are generally considered to define them and separate them from other hymenopterans (bees, wasps, and ants). There are two characters in particular that are important: an elongated scape (the first segment of the antenna) with an elbowed antennae and the metapleural gland (a gland found on the body of ants). While Sphecomyrma does have an elbowed antennae, it's scape is short. That being said, Sphecomyrma clearly possesses a metapleural gland (the exact function of this structure is unclear, but recent work strongly suggest it is involved in antimicrobrial functions and the secretion of various communication pheromones). The metapleural gland is particularly diagnostic for ants because no other hymenopterans possess anything remotely similar to it. Therefore, Sphecomyrma is considered an ant. It is not uncommon at all for ancient lineages of modern groups to possess some, but not all of the features we use to define them today (in this case the presence of short scape). Just so you know, there are now several known sphecomyrmines belonging to different genera (from two rather morphologically distinct tribes) that are even older (but not by much being around 95-100 million years old) than Sphecomyrma that have been discovered in French and Burmese ambers.

The next closest relatives to the ants is probably the Armaniidae which are an extinct group of large ant-like hymenopterans. We don't know much about them. Their exact placement has been hotly debated some have called them ants, some have not, and several researchers have variously flipped back and forth in their opinion. The reason is because armaniids, while being large, are only known from impressions in ancient rock (about 110 million years old) and they are very poorly preserved. Nothing resembling workers have ever been found for them (suggesting they were not eusocial), they have a wasp-like, very short scape, and they apparantly do not possess a metapleural gland.

Among living groups of wasps it remains unclear who is most closely related to the ants. Some have suggested vespids, others have suggested scoliids, and still other some of the more obscure wasp families, but I would say the jury is still out on this question. As for free will, I don't think ants have this - the concept of free will is very much a human construct. Ant colonies are more or less units that respond to their environment through chemical communication among nestmates."

Thanks again,
John LaPolla (guest expert), Corrie Moreau & the AntAsk Team

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