be  selected  of  districts  where  so  far  as  is  known  no  surface  water  exists 
in  an  area  of  twenty  miles  by  twenty — 400  square  miles — and  yet 
Gl.  morsitans  is  permanently  located  there.  This  is  perhaps  excep¬ 
tional,  and  it  is  unusual  in  the  part  of  North-Eastern  Rhodesia  where 
we  principally  travelled,  which  is  well  watered  by  streams  that  are 
rarely  so  much  as  ten  miles  apart ;  but  we  may  instance  that  to  the 
South-West  of  N’dola  in  North-Western  Rhodesia. 
It  is  often  stated  as  a  fact  that  this  fly  will  disappear  from 
habitations  erected  in  its  haunts.  This  would  appear  to  be  true  for 
North-Eastern  Rhodesia,  but  it  would  be  difficult  to  say  whether  it 
is  due  to  the  presence  of  man  or  to  the  inevitable  clearing  of  the 
bush,  with  the  consequent  destruction  of  its  natural  haunts,  necessi¬ 
tated  by  the  building  of  many  huts  and  the  making  of  gardens.  On 
many  occasions  we  have  taken  Gl.  morsitans  within  a  few  minutes 
of  leaving  a  village,  even  one  long  established ;  and  they  are 
frequently  located  sufficiently  close  to  follow  natives  daily. 
In  connection  with  ‘  following  ’  flies,  which  we  have  watched  being 
carried  by  natives  for  over  half  an  hour  without  attempting  to  feed, 
it  is  an  interesting  fact,  noted  alike  by  the  Administrator,  Mr.  Wallace, 
and  ourselves,  that  although  they  may  be  so  numerous  as  to  constitute 
a  perfect  plague,  most  of  them  will  quickly  disappear  when  a  camp 
is  made  in  the  midst  of  their  haunts,  and  also  even  if  the  halt  is  but 
a  temporary  rest.  On  the  other  hand  there  are  occasions  recorded 
where  our  first  capture  on  that  day  has  been  of  flies  apparently 
attracted  by  our  arrival  for  lunch ;  these  have,  however,  usually  been 
in  small  numbers,  ten  or  twelve  in  half  an  hour,  and  not  in  the 
swarms  so  often  carried  along,  where  that  number  could  be  captured 
with  one  sweep  of  the  net,  and  where  the  lining  of  one’s  helmet  and 
the  back  of  one’s  neck  would  be  almost  hidden,  if  for  a  minute  the 
energetic  use  of  a  fly  switch  were  discontinued. 
Local  numerical  variations  are  noticeable,  and  have  frequently 
been  noted  by  observant  residents  and  by  natives,  even  though  the 
meteorological  conditions  were  similar.  On  the  few  occasions  when 
we  have  travelled  more  than  once  over  a  piece  of  fly  country,  it  has 
been  rare  to  see  Gl.  morsitans  in  the  same  numbers :  on  some  such 
roads  in  the  Mpika  and  Chinsali  district  they  were  taken  plentifully 
in  April  and  May,  and  were  not  seen  in  September  or  December; 
again  at  other  spots  they  were  taken  in  these  latter  months,  and  were 
