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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 does not look like anything before on blankets, according to researchers online on April 21 in the Journal of Orthoptera Research.

In October 2017, herpetologist Frank Glaw toured the nocturnal rainforest of Amazonian Peru at the Panguana research station, searching for amphibians and reptiles. Its lantern passed over a brown mantis that mimics the leaves (Stenophylla lobivertex) in the vegetation tangle and saw “larval-like” structures sticking out of its back. Those structures were quickly sucked inside the insect after light struck it, says Glaw, of the Bavarian State Zoological Collection 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, the female blankets expel an inflated tip structure 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 that are found in the same section of the abdomen as the bifurcated S. lobivertex.

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Researchers rarely find this species of mantis and it can spread throughout the rainforest, so locating receptive pairs can be particularly difficult. The researchers think that a large gland of protruding pheromones with a lot of surface area could be an alternative solution, which more efficiently disperses pheromones to be detected by the antennae of pretending pheromones.

"It's a kind of 'chemical' dating application in the jungle," Glaw says, 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 they make a 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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