In any cannibalistic species, the mechanisms through which fecundity levels, offsprings benefit, and female performance increase as a result of male consumption must be explored. As mentioned, sexual cannibalism is exhibited in two main forms, precopulatory and postcopulatory. The mechanisms through which sexual cannibalism operates differ based on the type of sexual cannibalism exhibited by each species.

Pre-Copulatory Cannibalism

In populations in which precopulatory cannibalism occurs, the mechanisms that drive female decision to either mate with or devour a courting male and their ability to do so must be explored. As mentioned in the adaptive value section of this website, precopulatory cannibalism may result from female aggression. The genes given to any generation of female, even those that do not directly affect sexual activity, have the potential to play into the level of their aggression and subsequent responses to undesired male courtship. Undesirable genes may also dictate how females choose to kill potential mates. Insemination of genetically inferior males is not desireable. Male fitness plays a direct role in their survival during courtship not only because females often judge male fitness, but because more fit males are more likely to escape being eaten.

Post-Copulatory Cannibalism

In species where females are polyandrous and also control copulation duration, males have necessarily created mechanisms to ensure their mating attempts are not in vain. Many male species of spider let females begin to eat them during copulation to increase duration of copulation and ensure full sperm transfer.

Eunuch Phenomenon

From a male perspective, sacrifice or sexual mutilation results from necessity to ensure personal sperm success. The orb-web spider N. malabarensis is an excellent example of this. Orb-web spiders have been one of the most common types of invertebrates to perform sexually cannibalistic behavior. They exhibit extreme sexual dimorphism with the males being considerably smaller than the females. In N. malabarensis, males exhibit what is referred to as the eunuch phenomenon; males induce total genital emasculation in order to ensure that their sperm and only their sperm can inseminate the female. The palp, which transfers male sperm, is either partially or wholly ripped off and stuck into females to block further mating. These mating plugs directly prolong duration of potential sperm transfer and increase the amount of transferred sperm. While it seems maladaptive for a male to self-castrate himself, this behavior increases the reproductive success and the severed palps measured total sperm count has been shown to be higher than their unsevered counterparts, resulting in enhanced paternity.


Offspring Health

Many factors affect the health of the offspring sexually cannibalistic species.  The most important of these are temperature and nutrition availability. Some species of female spider such as Lycosa Tarantula females who often partake in precopulatory cannibalism were found to lay their egg sacs sooner in the year. Warmer temperature promotes more rapid egg development and subsequently healthier offspring. Additionally, females with higher quality diets produced eggs more rapidly. In species where the male is larger than commonly found prey, the calories obtained through either pre or postcopulatory cannibalism aids in egg growth. It is hypothesized that the earlier in the year spiderlings hatch, the more time they have to grow before having to mate themselves.

Is Cannibalism Nutritional?

True male nutritional value is largely contested, and there are huge differences in the nutritional value provided from different species of male spiders and praying mantids. In species where males are smaller than other common prey, cannibalism is not energetically favorable. It is proven however, that consumption of small males increases offspring survival.Even in populations of sexually cannibalistic spider surrounded by abundant high-quality prey, consuming a single male improves reproductive output, and so factors outside caloric intake must play a role. Eating a single male increased the number of offspring per egg sac by 30%, and these offspring had higher body conditions. If male nutritional value outweighs their paternal investment, it would have to be through subtle, or indirect ways.   Some hypotheses for these mechanisms which insure reproductive success are digestibility of male partners, the supply of nitrogen, a highly valuable nutrient for females, or supply of other nutrients that some females may be deficient in. It is also hypothesized that nutritional imbalance and poor health in certain species of spider results in an inability to catch prey that isn’t males of their own species. A final hypothesis for the mechanistic effects of male-provided nutrition in species of cannibalistic spider is that nutritional imbalance rectified by eating males may improve female ability to digest other prey.