The richest cache of food energy in the tropical forest hangs high in the trees – a pinata suspended out of the reach. These caches are filled with hundreds of white packets of sweets. These are the fruits of the labors of an insect colony – grown from resources gathered from every corner of the realm.
Those insects are paper wasps. They are like flying army ants – inspecting every crevasse high and low. They attack any bug, spider or worm they find – constantly bringing back provisions to their nest. The wasps forage through the flowers, harvesting pollen; they inspect the sap that oozes from tree bark for sweetness. Tireless hunters, they scavenge the carcasses of fallen animals, beached fish, dead frogs. They search out and collect everything they can find made of protein or containing sugar, live or dead.
Their suspended larders were not hung there just for the taking. The wasp’s nests are protected by the insects that built them. The surfaces of these nurseries are in motion all day long – covered in venomous stings, crawling with wasps that shock anything that touches them. Those stings have wings. The wasps are on constant alert – ready to rise as a swarm and deliver their painful defense in mid air.
The aggressive wasps have forced the sedentary creatures of the forest into hiding. They have taught all the other animals around them to jump at any surprise brush with any kind of insect. Passing monkeys or iguanas flinch just at the thought of an unbidden stinger alighting from above. Those denizens of the deep woods react to a buzzing over their head without thinking – an automatic, conditioned alarm response. They spin around searching wide-eyed until they have identify an innocent black and yellow beetle, or passing fly – then their panic subsides.
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The wasps are largely successful in defending their paper work. Their warning coloration and hostile disposition deter inquisitive coaties or toucans across a wide radius around the nest. But the wasps have been hanging those hives in plain sight for many millions of years now. There has been time for some predators to develop successful strategies for raids on the forest’s hanging pantries.
One such group of brigands is the army ants. They can muster a column of soldiers numbering in the millions. Their attack takes the form of a trail of crawling troops that stretches from the ground sixty feet or more up the trunk of a forest giant. The trail culminates at a paper nest suspended far out in the branches over the forest floor.
Different species of army ants each specialize in predation on different species of social insects – living inside tree trunks, or in holes in the ground, or in suspended nests made of thin pulp. The ants live in an olfactory world. Their scouts search through the scents they encounter. Some scents are repellent – warning them away from swaths of fungal rot or sticky, entrapping resin. The paper wasps have the capacity to coat the petiole from which their nest hangs with such scents – which repel army ants. This device renders the nest hanging below its mount invisible to the ants – most of the time.
A successful ant attack at a paper wasp nest will continue day and night. The attackers persist, mindless of the losses they suffer to the larger wasp defenders. They mount a war of attrition. Eventually, a point arrives at which the wasps appear to make a calculation.
The population of wasps at the nest is divided into two groups: the independently functioning winged adults, and the dependent, immature larvae. The adults work to foster the growth of their the colony, but their progress over the season depends on them and them alone – and not on the helpless nursery. The adults seem to know that their survival requires that they preserve themselves first. They can recover from nesting failure to build and populate a new nest in a new location. The immatures cannot do that.
In the face of an attack on their nest, the adults finally divide themselves from their young. They cut their losses, suspend their defensive effort and abscond. The invading ants then pillage the combs inside the paper walls – plundering all the larvae, pupae, and eggs. The nest will be left abandoned. It eventually becomes blotched with mold, soaked with rain, and dissolves into shards that fall away below.
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Few creatures in the forest realize how readily the wasps will give up on their formidable defenses. The creature that knows this the best glides in on broad wings to attack them. It is the Red-throated Caracara – a large hawk, as black as a vulture but for the red patch across the eyes and throat.
The caracaras are New World birds, named after the sound of their call. They are slow movers, with legs as long as a heron. They do not chase agile prey, as do the falcons – their close relatives. They focus on stationary targets. Many of them live as scavengers. The Black Caracara is a predator of bird nests.
The Red-throated Caracara is a predator of paper wasps. It is not frightened off by swarms of angry stingers. Its red legs and talons are too thick to sting through. It does not flee from the stings it suffers – it is unmoved by wasp venom. The bird uses its impervious eagle-like beak to crush stinging wasps. Defenders that attack its head are removed by the talons on the bird’s long legs.
The caracara attack begins with dive bombing. The initial impact of speeding raptor talons tosses the wasps on the outside of the hive away in all directions. With a clear line of attack, the hawk will rip the nest from its branch. If not, the dive bombing repeats – punching holes in the thin parchment skin.
Within minutes the wasps seem to sense an overwhelming assault. After the sacrifice of a few defenders, they evacuate, leaving the nest unguarded. The caracaras land upon it, and use their raptor beaks to tear into the paper wrap. They reach in through gaping rips, extract the combs, and clean them out.
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The paper wasps have persevered in the tropical environment, despite the co-evolution of their predators. To survive the attacks they face, they have entered into a multi-partite symbiosis with other insects and birds. All the members of this diverse group share a common nesting space. That is another story (to be posted later on this site) in which the Red-throated Caracara plays just a small part.
Kumar, A. et al 2009 Elevational patterns of diversity and abundance of eusocial paper wasps in Costa Rica. Biotropica 41, 338-346
McCann, S. et al 2013 Strike fast, strike hard: The Red-throated caracara exploits absconding behavior of social wasps during nest predation. PLoS One: 8:e84114