NATURALIST AT LARGE 



Bushels of Bots 



Africa's largest fly is getting a reprieve from extinction. 



By David A. Barraclough 



In the past 125 

 years all five of the 

 world's rhinoceros spe 

 cies — the Indian, Javan, and 

 Sumatran rhinos in Asia, and the 

 black and white rhinos in Africa — 

 nearly went extinct. And some of the 

 African rhinos were quite literally tak- 

 ing a large fly with them on their slide 

 toward extinction. Most people, even 

 in scientific circles, had no idea the fly 

 existed. They still don't. Certainly no 

 one considered conservation programs 

 for the fly while the rhinoceros popu- 

 lations were plummeting. Such a lack 

 of concern about threats posed to in- 

 sects and other invertebrates is not un- 

 common, but it is irresponsible. At 

 least 95 percent of all animal species in- 

 habiting the Earth are invertebrates, 

 and so they constitute the bulk of an- 

 imal diversity on the planet. Luckily 

 for the endangered rhinoceros fly, con- 

 servationists were inadvertently drawn 

 to its cause. 



The plight of the big, charismatic rhi- 

 noceroses caught the world's attention 

 in the 1990s; their populations had fall- 

 en drastically because of poaching, the 

 illegal trade in their horns, and the 

 destruction of their natural habitats. To- 

 day in Asia, only about 2,500 Indian, 

 3( II i Sumatran, and sixty Javan rhinos re- 

 main. Both African species, though, 

 have benefited greatly from sustained 

 and well-publicized conservation ef- 

 forts. The white rhinoceros, the world's 

 second-largest land mammal, has two 

 subspecies, one of which lives in south- 

 ern Africa and now numbers more than 



000. After declining to 

 as few as twenty indi- 

 viduals at the end of the 

 nineteenth century, 

 the southern white 

 rhino has become 

 one of Africa's biggest conservation suc- 

 cess stories. (The other white rhino, a 

 central African subspecies, numbered 

 more than 2,000 in the 1960s, but on- 

 ly five or ten individuals are left, mak- 

 ing it critically endangered.) Populations 

 of the black rhinoceros fell by a stagger- 

 ing 96 percent between 1970 and 1992; 

 the species is still endangered, but the 

 population has risen to 3,500. 



Rebounding from near extinction 

 along with the black and white rhinos 

 is a large fly, commonly known as the 

 rhinoceros bot fly (Gyrostigma rhinoc- 

 erontis), which parasitizes them. The 

 fly has the distinction — because of its 

 robust appearance and body weight — 

 of being the largest fly species known 

 in Africa. 



Like other bot flies, the immature 

 form of the insect is a spiny 

 maggot, or bot, that bur- 

 rows into its host and feeds 

 off the host's tissues — in this 

 case the gut of the black or the 

 white rhino. After three stages, 

 or instars, of growth, the mag- 

 got worms its way out through its 

 host's anus and metamorphoses into a 

 short-lived fly that can start the cycle 



Black rhinoceros (right) often hosts the larva 

 of the fly Gyrostigma rhinocerontis. The adult 

 bot fly, shown actual size on this page, is the 

 largest fly in Africa. 



over again by laying eggs on the hide 

 of its host. Because G. rhinocerontis de- 

 pends entirely on its hosts for survival, 

 its numbers would have mirrored the 

 rise and fall of rhinoceros populations 

 in all parts of Africa. In some periods 

 of the twentieth century, it must have 

 been close to extinction. 



About 24,000 known species of 

 flies, in slightly more than a hun- 

 dred different families, live in the 

 Afrotropics, a region that includes sub- 

 Saharan Africa, Madagascar, and asso- 

 ciated islands in the Atlantic and Indi- 

 an oceans. Beyond those species, a sub- 

 stantial number still await scientific 

 description and classification. Estimates 

 differ, but I would venture that at least 

 30,000 more African fly species remain 

 unknown to science. 



Even within that astonishing con- 

 text, few entomologists would dispute 

 the exceptional nature — both visually 

 and biologically — of G. rhinocerontis, in 

 the family Oestridae. The largest adult 

 specimens grow as long as 1.6 inches, 

 with wingspans as wide as 2.8 inches, 

 making it one of Africa's most striking 

 fly species. 



The rhinoceros bot fly was original- 

 ly discovered in the stomach of an 

 African rhinoceros more than 160 

 years ago. The adult form of the 

 species strongly resembles a 

 large, blackish wasp, with an djjfl 

 orange and reddish head 

 and long, slender legs 

 that are notably paler 



18 



naiukai history June 2006 



