Moths Mimic Spiders

Brenthia hexaselena, a species of metalmark moth,
flares its hind wings (HW) and spreads its forewings (FW) to mimic a jumping spider.

In lab trials, spiders caught 6 percent of the metalmark moths presented to them, as opposed to 62 percent of other moth species. What's more, the spiders sometimes made territorial gestures at the metalmarks -- and occasionally backed away.

For most moths, the sight of a jumping spider makes them panic as they try to escape its lethal pounce. But not so for metalmark moths in the genus Brenthia. These moths stand their ground with hind wings flared and forewings held above the body at a slight angle.

These moths are relying on mimicry to save their lives.

In that pose, the moth looks like a jumping spider, said Jadranka Rota, a graduate biology student at the University of Connecticut.

"That will actually save [the moth's] life," she said.

"The spider needs to act pretty quickly. Deciding whether the moth is potential prey or another jumping spider could take enough time to offer an advantage, in comparison to other moths."

Such mimicry usually allows the metalmark moth enough time for escape.

These experiments indicate that jumping spider mimicry is more widespread than previously appreciated, and jumping spiders are probably an important selective pressure shaping the evolution of diurnal insects that perch on vegetation.

The moth (upper image) mimics jumping spiders (lower image) with wing markings, wing positioning, posture, and movement (drawing by Virginia Wagner).

These moths survive encounters with jumping spiders more often than controls.

Moreover, jumping spiders respond to them with territorial displays that are normally directed towards other jumping spiders, indicating that Brenthia moths are being mistakenly recognized as jumping spiders, and not as potential prey.

Original paper, images.

Cited quotes.

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