Mechanism: a proximate explanation of the behavior based on physical and chemical characteristics of the animal.

The mechanistic details of sexual cannabilism are specific to each species that exhibits the behavior. By observing these difference one can find multiple triggers of cannabalism, mechanisms of cannabilism, and responses to cannabilism.

In Paruroctonus Mesaensis, or the dune scorpion, sexual cannibalism is a result of the scorpions natural feeding behavior. Scorpions have small hairs and slits on their legs that identify subsurface vibrations up to 50 cm away, allowing 360 degree detection during the nighttime. The scorpion abruptly turns, grabs the source of the vibration with its pedipalps (front claws) and attempts to club or sting the vibrational source with its metasoma (tail). This fixed action pattern, defined as an instinctive behavioral sequence that runs to completion (Campbell, 1996), in response to subsurface vibrations appears to be the cause of sexual cannibalism in Paruroctonus mesaensis because it is non-discriminatory, which would be problematic for male scorpions attempting to get close and mate with female scorpions.

In response to this predicament and eight step courtship ritual plus a mating dance are used by scorpions to indicate an interest in mating. The courtship ritual consists of multiple attempts (which are often successful) of the female attempting to kill and eat the male. The male raises his tail, struts, and judders to indicate his interests. This behavior begins a progression of desescalating and progressivel y less antagonistic touching until the scorpions initiate mating. This response illustrates one way a species manages sexual cannibalism due to a fixed action pattern (Polis & Farley 1979).

Praying MantisIn the Orb-web Spider (Nephilengys malabarensis) female sexual cannibalism of the male has affected male behavior in an interesting way. Orb-web males mate with females (who are 6x larger than males) by climbing up the females leg onto the abdomen and searching for the copulatory opening of the epigynum (the external genital structure of female spiders). Males then insert their palp (which transfers sperm) into the female and completely sever it from their bodies. This renders the male completely sterile. This may seem maladaptive at first glance, but viewing it in the scope of sexual cannibalism (which occurs around 75% of the time in this species) provides an explanation. One study has shown that breaking off the whole palp increases agility and endurance by shedding weight (Lee 2012). This increases the abi lity of the male to escape sexual cannibalism of the female and copulate again (male orb-web spiders have two functional palps).

Fitness Fig

Another study shows a correlation between the amount of time the palp is left in the female and the amount of sperm deposited (Li et al 2012). This allows for the male to deposit the maximum amount of sperm while escaping cannibalism or while being cannibalized.

If you're interested to see this behavior in action in the Praying Mantis, click here!