Neotrogla, a type of insect found in caves in Brazil, has a bizarre mating ritual. The act of reproduction lasts for days, and during the ritual, the female grows a penis-like structure called the gynosome. 

This is the first insect ever witnessed to exhibit complete sexual reversal during copulation. The act of mating can last between 40 and 70 hours. After the female grows a penis-like organ, she inserts it into an opening in the male, resembling a tiny vagina. 

Rodrigo Ferreira from the Federal University of Lavras in Brazil sent specimens of the creatures to Charles Lienhard, a Swiss insect specialist. During examination in Geneva, it became clear the insects were members of a new genus, and Lienhard noted the unusual appendages on some of the females.

Four species of insects make up the genus Neotrogla. The genus was first discovered in 1996, and adult specimens grow to be slightly longer than one-tenth of an inch in length.

The Neotrogla were examined by Yoshizawa and other team members, as they watched mating habits of the tiny insects. 

After females grow gynosomes and insert them in to a male, the organ swells and hooks pop from the appendage, anchoring itself to the inside of the recipient. The spiny features fit into pouches in the opening, keeping the male in place during the act. 

When researchers attempted to pull one female off her partner, the male insect ripped in half, with his organ still attached to the female. Sperm and nutrients are transferred from the male to his partner during the reversed copulation.  

Sexual role-reversal is practiced by several animals species, including some human beings. However, this is the first time the female of a species has ever been known to grow a penis-like appendage for copulation. 

Coercive sex is usually a male-on-female act in most species, but this is a rare example in nature of these roles being reversed. Researchers believe investigations of the unusual sexual habits of Neotrogla will assist in studies of sexual selection and diversity. 

"It will be important to unveil why, among many sex-role-reversed animals, only Neotrogla evolved the elaborated female penis," Yoshitaka Kamimura of Keio University in Japan said

Nutrition is hard to come by in the dark caves that house Neotrogla, and the male supplies these to the female, along with sperm, during copulation. Researchers believe this could encourage females to mate more often. 

Study of Neotrogla and their novel mating habits was detailed in the journal Current Biology

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