You may have seen wasps fighting and wonder just why they do it.
Wasps will often fight each other. Male wasps will often fight for the right to mate with female wasps which often results in death for the loser. Female parasitoid wasps, who insert their eggs into live hosts, often fight over the best specimens to enable their young to prosper. Paper wasps will also fight for the right to become queen.
Solitary Parasitoid wasps fight over bugs to insert their eggs into.
Many solitary wasps are parasitoid, which means that they insert eggs into other bugs and spiders. The eggs hatch inside the bugs and then somewhat gruesomely develop and eat the inside of the bugs until eventually eating their way out. Often all this happens while the host bug is still alive. See this article about the Tarantula hawk.
Choosing the right bug to insert eggs into is important as if it is too small there won’t be enough food for the growing larvae to fully develop. As a result, these solitary wasps will often fight each other for the best host bugs.
A study found that the bigger the bug the harder these wasps fought each other for it. It also found that older wasps fought harder than younger wasps, presumably because they knew it was their last chance to successfully produce offspring. (Source)
Paper wasps fight to decide who will be queen
While most social wasp species have queens born with distinctly different characteristics than the other wasps in the colony, this is not true of the paper wasp (Polistes fuscatus). Any paper wasp can become the queen. As a result, they will fight each other for dominance.
To avoid wasps continually rehashing the same battles with the same wasps, evidence has been found to suggest that these wasps have a way of recognizing, or remembering the others. This may even be through facial recognition. A study at the University of Michigan vied wasps against each other but found that when wasps that had previously fought were placed together at a later date they declined a rematch. (source)
Do wasps fight to the death?
Fighting to the death is not usually in any animal’s interests but it seems male parasitoid wasps don’t have such qualms. In may solitary wasp species there are far fewer males than females. In fact, in many wasp species, male wasps are born for the sole purpose of mating before dying.
The wasps you see buzzing around your picnic are almost exclusively going to be female. The female worker wasps are tasked with feeding and protecting developing larvae. Male wasps are tasked with mating.
The males fight each other for the right to mate with the females. Often the losers will end up being decapitated. They have one opportunity to mate in a short period of time and will fight to the death for the right.
Most wasps will not survive the winter. In social wasp species, only queen wasps survive the winter by hibernating. All other wasps will die in the winter. Their short lives mean they don’t really have much to lose by not fighting for the right to mate.