|Photo by Jen R|
The culprit of this gruesome attack is the Emerald Cockroach Wasp (Amuplex compressa), a 2-3 centimetre long insect of a startling blue-green colour with vibrant red upper legs. Remarkable in its colouring and delicate in build, the beautiful, fragile female wasps can single-handedly and viciously attack their sturdy cockroach victim. Targeting specifically the American cockroach (Periplaneta Americana), the wasp undertakes a complex sequence of behaviours involving a brutal wrestling match followed by two consecutive stings to the midsection and head of the prey. The latter of these stings penetrates directly into the nervous system, the venom injected seeping into that organ to throw the cockroach into a daze. What follows is a brief feed by the wasp upon the victim’s haemolymph (the insect’s blood) by tearing off the antennae to access the nutritious fluids. Upon eating her fill, the female conducts a puppet master-like act of nudging the now zombified cockroach into a burrow where it is buried alive with a single egg glued to its belly. When the larva emerges, it proceeds to nibble into the fresh prey, even crawling inside the roach to continue obtaining nourishment. Gradually, as its internal organs are consumed, the cockroach dies and its hollowed out body become a shell in which the larval wasp spins a cocoon to undergo pupation. At a point of 6 weeks after initial burial, the new wasp breaks out of the carcass and emerges from its burrow.
This complex and potentially dangerous sequence of behaviours conducted by the female wasp involves a certain amount of skill and apparent calculation. From overcoming the cockroach to injecting venom directly into the nervous system to ensure maximum effect, and finally burying the host with their larva, each step is essential in ensuring optimal development of the offspring. How did such a small creature acquire the skills to perform this violent yet evidently effective attack? A team of researchers conducted a study to determine whether such efficiency is a product of learning, and as such improving with experience, or whether the knowledge was wired into wasps before birth. The researchers observed the successive attack and burial of cockroaches by 10 individuals in 4 instances each, observing the efficiency and precision of the wasps' behaviours.
The consistency of this highly complex and specific set of behaviour was found to change little with experience. That is, gaining experience did not improve the performance of the female wasps. The time taken to attack and bury did not become more refined, though at times the ordering of the sequences was altered. The viciousness and efficiency of the behaviours is not learned but innate; these wasps were born with all the knowledge they needed.
This demonstration of skill is just one example of the incredible abilities of insects. Despite lacking in parental care after birth, and hence not afforded the chance to learn from their parents, the newly born wasps are gifted with the ability to continue in the behaviours required for survival and reproduction. Emerald Cockroach Wasps has become a specialist in the most effective method of subduing their target; an evolutionary triumph for the wasp, though not in the least bit positive from the perspective of the cockroach.
Keasar, T., Sheffer, N., Glusman, G., & Libersat, F. (2006). Host handling behaviour: An innate component of foraging behaviour in parasitoid wasp Ampulex compressa. Ethology 112: 699-706
This post was written by Holly Cooper