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This religious mantis inflates a strange pheromone gland to attract companions

Religious blankets, with their angular features, huge eyes, and centaur posture, often look a little alien. But researchers have recently found a species of mantis that takes this otherworldly quality to the next level: females of this species have an inflatable pheromone gland that protrudes from the back of the abdomen like a Y-shaped green balloon.

This strange organ is different from anything seen on blankets before, according to researchers online on April 21 in the Journal of Orthoptera Research.

In October 2017, herpetologist Frank Glaw was moving through the nocturnal rainforest of Amazonian Peru at the Panguana research station, searching for amphibians and reptiles. His flashlight passed over a brown, leaf-like mantis (Stenophylla lobivertex) in the vegetation tangle and saw "larval-like" structures protruding from his back. Those structures were quickly sucked inside the insect after light struck it, says Glaw, of the Bavarian State Collection of Zoology in Munich, Germany.

Glaw was reminded of "the parasites that eat the animal from within," as they had previously seen insects so fatally parasitized. With the help of Christian Schwarz, an entomologist at Ruhr-University Bochum in Germany, and observations of some captive female specimens, the team discovered that the mantis was not a parasitic vessel.

The inflatable pheromone gland of Stenophylla lobivertex (shown) can be highly efficient at spreading chemical signals through the rainforest.Christian J. Schwarz (CC-BY 4.0)

When left undisturbed in total darkness, female blankets protrude into a toothed structure inflated with body fluids, roughly the tone and luster of polished jade. It appears to be a highly modified gland to produce pheromones, chemical signals that help female insects attract mates (SN: 13/05/15).

Other blankets have simple, non-inflatable glands found in the same section of the abdomen as the bifurcated apparatus of S. lobivertex.

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This species of mantis is rarely found in researchers and could spread finely through the rainforest, so locating receptive pairs could be particularly difficult. The researchers think that a large, protruding pheromone gland with a lot of surface area could be an alternative solution, which more efficiently disperses pheromones to be detected by the antennae of suitors.

"It's a kind of 'chemical dating' application in the jungle," says Glaw, noting that the observations "emphasize the importance of pheromones in the reproduction (of mantises) in a living way."

Females of some other mantis species are known to exhibit a pink gland and patch when performing their chemical call by mates, says Henrique Rodrigues, an entomologist at the Cleveland Museum of Natural History who did not participate in this research.

“I can see something like the precursor of the protruding gland,” Rodrigues says. He notes that since males have thin, hairy antennae, "the other way to increase the chances of finding a mate would be for females to increase the amount of pheromone released."

Glaw believes that similar glands are likely to exist in the other two species of Stenophylla and possibly in other mantises. "If this organ is really an important tool for improving mate discovery," he says, "it would also be an advantage for many other mantis species and could be more widespread."

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