Sexual Cannibalism in Praying Mantises

Insect world continues to fascinate us with the diversity in all aspects. Insects have amazing adaptability, strength in comparison to body size, ability for metamorphosis, and so on.

Praying mantis are one cool and photogenic group due to their eyes, face posture and forearms. I love watching them and can spend a lot of time just looking at their movement or feeding style.

While walking casually between two university buildings, I noticed some insect in the grass. From a distance I thought it was a grasshopper or Katydid. But I decided to take a closer look. It was a Praying Mantis. 

But it looked a little different. I then realized it was not single insect but was a mating pair. But then the male looked weird. It took some time for me to realize that the head of the male was missing.

I immediately remembered reading about sexual cannibalism in mantises. But I was thinking it happens after the mating is complete. The females many times catches and eats the males. There are different theories about this. In most predatory species this is observed. It is a very high percentage in captivity but is known to occur in the wild in about a fourth of times. 

I never thought that I would get to see such an event in wild myself. Most interesting thing was the mating was still in progress even though the male was headless. And half an hour that I observed the male was still in the same position and the female was not attempting to attach further. 

Update:  It is a Carolina Mantis (Stagmomantis carolina) in Mantids Family (Mantidae) thanks to Kris Anderson (Author of: “Praying Mantises of the United States and Canada” ISBN# 978-1717825735 Second Edition) for confirmation of the identification.

I also got some really informative notes from Kris:

"It appears to give the female a boost of energy needed in order to properly produce eggs. The males are aware of this, and there have been tales from the mantis-keeping community of males cutting off their own heads and offering it to the female before mating. It's also the reason why mating takes so long. Insemination of the female only takes about 15 or 20 minutes, but males are scared to get off, so they often stay attached for several hours, even days.

Bear in mind that cannibalism during mating is a species-specific behavior. Many (most) Mantodea species do not engage in this practice at all. For those that do, the behavior generally occurs <25% of the time and almost always involves a nutritionally starved female. The duration of copulation itself is also a species-specific endeavor, as is courtship. There are multitudes of variations and combinations with courtships, copulation, and cannibalism with the absence or presence of each behavior among the myriad species for various evolutionary benefits. Regarding the species photographed, Stagmomantis carolina:

Females readily mate 1-3 days after their final molt. Males demonstrate interest in mating 1-5 days after their final molt. Mature males will visually track receptive females for a few seconds to several minutes before rapidly pouncing upon them, which may evoke aggression from the female. Rarely will males stalk the female for an hour or more. Males typically mount the female from behind and may remain clinging to her for several hours before copulating. Occasionally, males will temporarily invert their position while initially mounting atop the female to seemingly examine the female’s genitalia. They will then right themselves and continue clinging onto her body or initiate copulation. Mating generally lasts for 6-8 hours but occasionally spans 1-2 days. Multiple males may mount a female simultaneously but only one can engage in copulation. Cannibalism during mating occasionally occurs with most well fed females showing no aggression throughout the process. Surviving males will typically slough off the female after copulation and feign death for several minutes or simply fly away. Males may also remain mounted to the female after copulation has been discontinued, which further endangers them to cannibalism regardless of the female’s appetite. Both sexes may mate multiple times with the same partner or with different conspecifics. Rarely, males will mount other males and may attempt to copulate. Males have also been noted to mount immature females and demonstrate no impairment in mating behavior with their antennae removed, suggesting that visual cues alone, not necessarily pheromones, are highly influential toward locating females. Males that survive copulation die naturally approximately 1-3 days later. Unmated males will usually perish approximately 1 month after final molt regardless."

and Tyler Christensen:

"Very cool observation! This behavior is probably to help increase the fecundity of the female, but the male is usually not self sacrificial (unlike some Lactrodectus species). It appears to be related to the number of potential mates a male can have. If a male can have multiple mates, it’s better to try and survive a mating attempt than to submit to sexual cannibalism. However, this can change depending on how many mate encounters a male has. The fewer mates encountered, the more risks a male will make when mating."

References:

• iNatrualist record
• iNaturalist blog