Chap. 30 



ARTHROPODS INSECTS, SPIDERS, AND ALLIES 



591 



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Fig. 30.2. Termites. Buildings of the magnetic termites (Hamitermes meridio- 

 nalis) or white ants near Darwin, Australia. They are slabs of peaty soil whose long 

 axes lie almost exactly north and south. Within them millions of termites populate 

 the passageways and the chambers are filled with grass collected in the wet season 

 (November to April) and stored to last through the dry season (May to October). 

 On a smaller scale termites in the milder climates of the United States build 

 similar passageways in wood. (Photograph by W. Brindle. Courtesy, Australian 

 National Information Bureau.) 



spring. Warm damp evenings murmur with mosquitoes and a meadow lighted 

 by fireflies tells more about their numbers than can be written. In autumn, 

 ladybird beetles turn gregarious and pack together in protected spots for the 

 winter. In northern California, ladybirds {Hippodamia convergens) go to the 

 mountains in winter and hide under the pine needles in sunny slopes. Two per- 

 sons working together can collect 50 to 100 pounds of them in a day and 

 since each beetle weighs about 20 milligrams, a day's catch is estimated to be 

 at least one to two and a half millions. 



The reproductive capacity of insects depends upon the number of eggs laid 

 and the length of time it takes for an egg to develop into an adult. "Seventeen 

 year locusts" are 17 years old before they produce eggs, but most insects 

 mature within a year or less. A grand climax is attained by aphids with 30 

 generations in a single season, nearly every one wholly made up of productive 

 females and each generation a stepping stone to a larger generation. Aphids 

 must be a pleasure to mathematicians. Herrick calculated the weight of cab- 

 bage aphids that produce 12 parthenogenetic generations between late March 



