Survival Value two shrimp

When the Mantis shrimp molts, it always increases the rate of threat displays from its burrow. The stomatopod will be making far more false threat displays than it would make normal displays if it had functional weapons. This serves to increase the chance of survival among molting stomatopods despite lacking defensive capabilities (6, 10).

Picture from http://www.corbisimages.com.


Depending on the size of the stomatopod, a threat display can deter attackers even if there is no chance of the molting stomatopod injuring the aggressor. Stomatopods tend to use ritualized non-violent fights to lower the casualties within the species (1). This allows a violence-free display to lead to success.

Therefore, it is favorable for stomatopod populations to include threat displays as it is a less costly form of conflict, and it gives the possibility of victory for a physically weaker individual, such as a molter (1,6). An individual will have a greatly increased life expectancy as a result.

It is important to realize that such threats benefit both the weakest and strongest individuals because a physically weaker individual will win conflicts that it normally would not. On the other hand, a stronger animal will grab easy victories with a simple intimidating threat. However, these false threat displays do not benefit those that are not especially strong or weak; they have a chance of losing to a weaker member, but little chance of beating the stronger (5).

In Stomatopoda, the mechanics of the molting period cause each animal to go through frequent cycles of weaker and stronger. Therefore, these false threats increase the fitness of individuals because each will spend time as the weaker combatant during certain periods of time. It is even possible for a molting stomatopod to have a better chance of survival than a non-molting one due to the fact that molters display even more aggressively than normal in their weakened condition.

Below is a table from Rick Steger and Roy Caldwell's paper on false threat displays in molting stomatopods; notice that the proportion of wins to losses goes up for new molts that displayed rather than hid or fled.

display rates

Image from Science, volume 221, page 558.