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Fighting back? August 23, 2006

Posted by thebeam in The Byways.

Prompted by a story coming out of Alabama, where some extremely large nests of Yellow Jackets have recently been found. From The MontgomeryAdvertiser,

Entomologist Dr. Charles Ray at the Alabama Cooperative Extension System in Auburn said he’s aware of about 16 of what he described as “super-sized” nests in south Alabama.
Ray said he’s seen 10 of them and cautioned people about going near them because of the yellow jacket’s painful sting.
The largest nest Ray has inspected this year filled the interior of a weathered 1955 Chevrolet parked in a rural Elmore County barn. That nest was about the size of a tire in the rear floor seven weeks ago, but quickly spread to fill the entire vehicle, the property owner, Harry Coker, said. Four satellite nests around it have gotten into the eaves of the barn, about 300 yards from his home.

I wonder if this is but a foretaste of what is to come.

My college education dealt largely with digging into the background of what controls populations, and when I saw this article I was immediately struck with several theories, almost all of them not good. Global Warming is a possibility, one not high on my list; but I did start thinking about why insects, and wasps in particular, nest.

A brief search brought me to some papers by someone whose work I was familiar with, an Associate Professor in the Animal Behavior program at the University of Washington, Sean O’Donnel PhD. From two of his papers we can see a possible reason develop.

The nest as fortress: defensive behavior of Polybia emaciata, a mud-nesting eusocial wasp.

Predation on swarm-founding wasp nests by bats (Jeanne, 1970a), birds (Skutch, 1971; Windsor, 1976), and primates (Vecht, 1967) has been documented. Vertebrate predation can be a major source of epiponine colony mortality. We hypothesize that the unusual defensive response of P. emaciata is a behavioral adaptation to its use of mud in nest construction, which may make the nest more resistant than paper to entry by vertebrate predators. It appears that the wasps initially rely on the nest itself, rather than on exit and attack behavior, to thwart vertebrate predators. We suggest that this represents a special type of architectural defense (Hermann and Blum, 1981), where the defensive behavior of a species has been modified to exploit the properties of its nest material. However, P. emaciata nests are not impregnable. Skutch (1959) observed a red throated caracara (Daptrius americanus) removing combs from a P. emaciata nest and feeding on the brood in Costa Rica. Our subject nests often responded with attack behavior after extended disturbances, suggesting that attack can be effective for this species. When attack did come it was sudden and massive, suggesting that it was coordinated by an alarm pheromone, as has been demonstrated for P. occidentalis (Jeanne, 1981). Although army ants are among swarm-founding wasps’ most frequent predators in wet tropical habitats, preliminary tests on the reaction to Eciton army ants did not suggest that P. emaciata ’s mud nest is effective in resisting these predators (Chadab, 1979; S.O’D. personal observation).
The use of mud as a nesting material may have evolved in response to predation pressure, particularly by vertebrate enemies. Similar advantages against hornet (Vespa) predation may have favored the evolution of mud construction in hover wasps of the genus Liostenogaster (Hansell 1984; Turillazzi 1991). However, mud construction appears to provide other benefits. Our observations suggest that P. emaciata mud nests damage, than similarly sized paper nests. Schremmer (1984) analyzed the water repellent properties of P. emaciata nest material. Even if increases in general durability were the original selective advantage driving the evolution of mud construction, the workers’ defensive behavior has apparently been secondarily modified.

Clearly, from this article, the choice of construction material, as well as possibly the size of the nest, are both influenced by predation.

Another paper by Professor O’Donnel, Correlated evolution of colony defence and socialstructure: A comparative analysis in eusocial wasp (Hymenoptera: Vespidae), talks about increasing size, as well as advantages to having multiple queens in a single nest.

Animal societies depend on effective defence of group resources. Defensive mechanisms can be costly and may constrain the evolution of social structure. We analysed how exocrine mechanisms of colony defence were affected by the evolution of social complexity and of nest architecture in paper wasps (Vespidae). Eusocial paper wasp species exhibit two discrete grades of eusociality, with new colonies founded either by queens or by coordinated swarms of queens and workers. Swarm-founding shows multiple evolutionary origins from independent-founding ancestors within the Vespidae. Nest architecture also varies among paper wasps. Nests with covering envelopes evolved from naked combs several times. We hypothesized that: (1) evolutionary transitions from independent- to swarm-founding would obviate the need for chemical defence against ants and (2) transitions from naked combs to enveloped nests would have a similar effect on chemical defence. In support of the first hypothesis, we found that all independent-founding species possess ant-repellent glands (Van der Vecht’s gland), while many swarm-founders do not. Furthermore, phylogenetic analysis suggested that evolutionary loss of this gland was statistically more likely to follow transitions to swarm-founding. Evolution of nest envelopes was less strongly associated with losses of the ant repellent gland. These patterns suggest that maintenance of defensive exocrine glands is costly. The patterns also suggest that group behavioural defence against ants is a key adaptive feature associated with the evolution of swarm-founding. The hypothesis that the evolution of nest envelopes obviated chemical defence against ants was not as well supported.

Living in social groups imposes a number of costs on members (Alexander, 1974). For example, many animal societies accumulate resources (brood and food stores) that attractconspecific and heterospecific natural enemies. These resources must be defended, and defence incurs some cost to the society. Recent theory suggests that defensive adaptations correspond to evolutionary transitions among different social systems (Starr, 1985; Costa and Pierce, 1997; Crespi and Choe, 1997; Wolff and Peterson, 1998; Hunt, 1999). Comparative analyses can provide empirical tests for correlated evolution of defence and social systems. We performed a test for correlated evolution of social structure and defence in paper wasps (Vespidae) that exhibit different grades of eusociality. Our aim was to quantify the relationships of evolutionary transitions in mode of colony foundation and in nest architecture with the evolution of exocrine defensive mechanisms.

While not exactly on point, the general theme of the article is that the wasps exhibit adaptive social behavior in response to the level of predation that they encounter. A given species, in an environment where predation is low, will opt for smaller colonies with a single queen. However, if the pressure rises, it becomes more advantageous to the species, if the size of the colonies increases, and a dozen or more queens be used to breed in the colony.

What this all may mean, <emphasis on “may“> is that wasp populations in that region have discovered a new enemy or predator. If that predator is another population of insects, or just some unseasonable weather, expect this behavior to fade away next year, and the nest sizes reduced to more normal. However, mankind tends to make changes that are slow to develop, and even slower to abate. If we are the cause, we might expect this behavior to become more common, and the reports of massive attacks of wasps to rise accordingly.

Who knows what other treats nature has in store for us?

Life and Hearts is in session. Are you ready to “Hunt the bitch?”



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