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Museum of Arts & Sciences 



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Florida Museum of 

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Gainesville, Florida 

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Orlando Science Center 

 Orlando, Florida 

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 a new hands-on experience 



Mary Brogan Museum of 

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 Tallahassee, Florida 

 featuring "DINOSAURS: 

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 through May 14 



Museum of Science & Industry 

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Tampa, Florida 

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tions. Acropyga epedana, for instance, in- 

 habits the dry mountains of southeast- 

 ern Arizona [sec photograph on page 22]. 



The behavior of modern species of 

 Acropyga shows a great deal about 

 what life was probably like for A. glae- 

 saria. All Acropyga species are small, yel- 

 lowish ants, with workers no bigger 

 than two to four millimeters long. The 

 ants live almost entirely underground. 

 The workers retreat quickly when ex- 

 posed to light, as the burrowing work- 

 ers on prehistoric Hispaniola may have 

 done. Instead of foraging above- 

 ground, a common practice among 

 many ants, Acropyga workers remain in 

 underground chambers, where they 

 "herd" and "milk" the insect equiva- 

 lent of cattle. The "cattle" for the 

 Acropyga are small, white mealybugs 

 that feed on the underground roots of 

 various plants. As the mealybugs feed, 

 they secrete a sugar-rich fluid called 

 honeydew, which seems to meet all the 

 nutritional requirements of the ants. It 

 seems as if each species of Acropyga has 

 a single — or, in some cases, a few — 

 species of mealybug associated with it. 



I have studied Acropyga ants from Ari- 

 zona to Guyana to South Africa. To 

 find them, you turn stones over one by 

 one and patiently break apart rotting 

 logs, looking for tiny, slow-moving 

 golden flecks. During my field studies 

 in Guyana, I was fortunate enough to 

 discover three new Acropyga species, 

 along with two new species of mealy- 

 bugs associated with Acropyga. Finding 

 and identifying the mealybugs that live 

 with Acropyga is the first step in under- 

 standing the organisms' complex sym- 

 biotic relationship. 



Some of the most familiar species of 

 mealybug live aboveground; they are 

 well known because some are garden 

 pests. By contrast, the various species 

 tended by Acropyga depend entirely on 

 the ants for protection and survival, just 

 as the ants rely on them for food. That 

 special kind of symbiosis is known as 

 trophobiosis — ants care for another or- 

 ganism, called the trophobiont, in ex- 

 change for food. Many other ant spe- 

 cies, in genera other than Acropyga, 

 gather honeydew from insects such as 

 mealybugs and aphids. In fact, in North 

 America it is common to see ants tend- 



Worker ant (A. acutiventris), belonging to the same genus as the fossilized 

 ant in the photomicrograph on page 16, carries a white mealybug to 

 another part of her nest. At the bottom of the image, a "herd" of 

 mealybugs congregates near a plant root. Biologists think ants and their 

 mealybug "cattle" may have co-evolved. 



20 



NATURAL HISTORY May 2006 



