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Dragon mantis females have a Y-shaped sex gland that moves like a tentacle and looks like a maggot

A close-up of the pheromone gland in a Stenophylla lobivertex female.
A close-up of the pheromone gland in a Stenophylla lobivertex female. (Image credit: Christian J. Schwarz)

Female dragon mantises aren't subtle about letting males know that they're ready for sex. When it's mating time, females of this rare praying mantis species inflate a glistening, greenish gland that juts up and outward from the lower part of their abdomen. 

The structure has two branches, so it resembles a very small, moist balloon in the shape of the letter "Y," and it emits pheromones that males find irresistible. Sexually receptive females puff up the gland at night "and only when undisturbed," scientists recently reported in a new study. 

Other types of mantids emit pheromones from small bulges in their abdomens, but in those mantises the bumps protrude only slightly, if at all. The dragon mantis (Stenophylla lobivertex) is the only known mantis in which females have evolved a blow-up sex gland of this size, according to the study.

Related: Lunch on the wing: Mantises snack on birds (photos) 

Dragon mantises are found in Ecuador and Peru, and are known from only a handful of specimens. Adults measure about 1.6 inches (40 millimeters) long, and the brownish-green color and texture of their bodies resemble that of dried-up leaves.

The Y-shaped glands, however, look shiny and damp. When fully inflated, the gland measures 0.2 inches (6 mm) long, is about 0.04 (1 mm) thick at both ends and each lobe "can also be moved in a tentacle-like manner," the researchers wrote. In fact, that movement led the study author who discovered the unusual gland to suspect that the mantis had been infected by a parasite.

"When I saw the maggot-like structures peeking out from the back of the praying mantis and then withdrew, I immediately thought of parasites that eat the animal from the inside, because that is not really uncommon in insects," Frank Glaw, a reptile and amphibian expert at the Bavarian State Collection of Zoology in Munich, Germany, said in a statement.

Female dragon mantises are the only known mantis species to possess an inflatable pheromone gland of this size. (Image credit: Christian J. Schwarz)

When the scientists investigated the structures more closely, they found that the glands were filled with hemolymph, a bloodlike fluid in invertebrates. Threadlike tubes called trachea, which carry air to insects' tissues, were visible through the gland's thin membrane. 

The researchers observed mating behavior in four female dragon mantises: one in the Peruvian Amazon, and three captive females obtained from a breeder in Germany. During the observation periods, which were conducted over several months for each group, females inflated their glands and emitted scent-calls at night for about 2 to 5 hours. They only did so under cover of darkness and when they were left undisturbed. If the mantises were interrupted or distracted while waggling their shiny love sticks, "the pheromone gland was retracted instantly," the study authors wrote. 

Because the insects are so rarely glimpsed in the wild, they are thought to be scarce in their native habitats. Waving an inflatable come-hither sex gland could therefore help dragon mantises find each other more easily, which could be critical for the species' survival, lead study author Christian J. Schwarz, an entomologist at the The Ruhr-University Bochum in Germany, said in the statement.

"We suspect that Stenophylla lobivertex can release the pheromones with the protrusible organ more efficiently and in a more targeted manner than other praying mantises," Schwarz said. "This can be very important, especially for rare species with a low population density, so that males can reliably find their females."

The findings were published online April 21 in the Journal of Orthoptera Research.

Originally published on Live Science.

Mindy Weisberger
Mindy Weisberger is a senior writer for Live Science covering general science topics, especially those relating to brains, bodies, and behaviors in humans and other animals — living and extinct. Mindy studied filmmaking at Columbia University; her videos about dinosaurs, biodiversity, human origins, evolution, and astrophysics appear in the American Museum of Natural History, on YouTube, and in museums and science centers worldwide. Follow Mindy on Twitter.