William and the Mantidfly’s Familiar Arms

By half past midnight, William had reduced the desk to a pool of lamplight and two close-up insect photographs.

On the left, a praying mantis. On the right, something that appeared to have ordered the same front legs and economised on the rest.

He traced the mantis’s folded foreleg with his pencil tip, hovering just above the photograph: the thick segment, the spines, the lower segment closing against it. A trap carried ready beneath the head. Then he moved the pencil to the other photograph and followed the answering fold.

Same weapon. Different family trees.

The second insect was a mantidfly, a member of Mantispidae in the order Neuroptera—a relative of lacewings, not a small praying mantis. Its delicate, net-veined wings made the borrowed-looking armament seem almost unreasonable. But nothing had been borrowed. These grasping forelegs had evolved separately in the two lineages.

William set the pencil between the pictures. Resemblance was a useful clue. It was also perfectly capable of sending you to the wrong address.

Convergent evolution: similar pressures arriving at similar equipment. Here, the problem was catching prey and keeping hold of it. The answer folded neatly.

Below the mantidfly photograph, his notes took a stranger turn. In many mantidflies, the first larval stage is an active seeker, finding a spider and riding it or entering its egg sac. Once established with that supply of eggs, the larva feeds and changes into a much less mobile form. Hypermetamorphosis: a life whose early search party and later resident hardly seem designed for the same job.

He looked back at the adult. Those conspicuous arms had offered him an instant explanation of the whole insect. They explained one task, not its ancestry, and certainly not its whole life.

William wrote beneath the photographs: “Matching tools are not a family portrait.”

Then he traced both folds once more. The resemblance had not become less striking now that he understood it. It had become twice as strange.