Despite not being terribly smart as individuals, wasp (黃蜂) colonies build and maintain a complex nest that lasts many generations. Just how these social wasps coordinate this task has always been a mystery. But now a mathematical model suggests that one key factor drives their behavior: the amount of water in the nest.

　　Social wasps cannot learn from one another --- unlike bees, which use a complex dance to tell nest mates where sources of nectar (花蜜) are . Nor do they use pheromones (信息素) the way ants do to lead other ants to food.

　　Robert Jeanne of the University of Wisconsin-Madison proposed that wasps set up a demand-driven chain of information. At the end of the chain, builder wasps monitor the nest and when necessary, request pulp from pulp forager wasps. They in turn demand water from water foragers in order to make the pulp.

　　But biologist Istvan Karsai of East Tennessee State University in Johnson City, Tennessee, and his team found that social wasps in Panama don’t actually work that way. They removed either builders or pulp foragers from a colony of a species, called Metapolybia aztecoides. Although that should break up the so-called information chain, it did not significantly alter the amount of water being brought into the nest. They also found that the wasps could change roles, something that Jeanne didn’t expert. For instance, when the researchers sprayed a surplus of water onto the nest, water foragers quickly became builders, and nest building increased.

　　Based on their observations, Karsai’s team developed a mathematical model that shows that wasps achieve their complex behavior simply by monitoring the level of water in the nest — what he calls the “common stomach” of the colony. He believes wasps infer what the level is when they exchange fluids on meeting each other, a behavior called trophallaxis that is common in many social insects.

　　To test the model, Karsai simulated changes in the model colony, for example by removing pulp foragers or builders. “What’s interesting is that in every case the model responds like the actual colony in Panama, “says Karsai.

　　27. According to the passage wasps _____ .

　　A. are very smart as individuals

　　B. are able to build and maintain complex nests

　　C. drink more water than scientists have expected

　　D. can learn from each other just like the bees

　　28. What can we infer from the first two paragraphs?

　　A. Bees are smarter than wasps.

　　B.Wasps have nothing in common with bees.

　　C. Unlike bees, wasps live in colonies.

　　D. Wasps use pheromones to lead other wasps to food.

　　29. Robert Jeanne believes that _____.

　　A. the wasps colonies are the ideal social colonies

　　B. wasps have very strict hierarchical classes

　　C. wasps’ behaviors depend on their demands

　　D. builder wasps have a higher status than pulp forager wasps

　　30. Istvan Karsai and his team have found that _____.

　　A. water distribution in the wasps colonies is based on the kind of job the wasps are doing

　　B. when the information chain is broken up in the wasps colonies, the amount of water decreases

　　C. when a surplus of water is sprayed onto the wasps nest, the water foragers refuse to work

　　D. wasps change roles according to the situations in the nests

　　31. The word “trophallaxis” is closest in meaning to _____.

　　A. the level of water in the nest

　　B. the common stomach of the colony

　　C. the exchange of fluids on meeting each other

　　D. common social insects

　　32. The following statements are related to the mathematical model developed by Karsai’s team EXCEPT that _____.

　　A. wasps achieve their complex behavior simply by monitoring the level of water in the nest

　　B. what Karsai calls the “common stomach” of the colony

　　C. wasps infer what the level is when they exchange fluids on meeting each other

　　D. common in many social inserts