﻿The 
  British 
  Species 
  of 
  Andrena 
  and 
  Nomada. 
  225 
  

  

  larvae 
  fed 
  on 
  food 
  quite 
  as 
  different, 
  as 
  that 
  supplied 
  to 
  

   each 
  generation 
  of 
  the 
  double-brooded 
  species. 
  Andrena 
  

   spinigera 
  is 
  the 
  most 
  interesting 
  of 
  all 
  these 
  forms, 
  since 
  its 
  

   second 
  brood 
  undergoes 
  such 
  marked 
  changes 
  in 
  structure 
  

   as 
  to 
  become 
  very 
  similar 
  to 
  the 
  single-brooded 
  A 
  . 
  trimmer- 
  

   ana 
  (Auct. 
  nee 
  K.), 
  whereas 
  the 
  (^ 
  of 
  its 
  first 
  brood 
  {i.e. 
  

   typical 
  spinigera) 
  is 
  quite 
  distinct 
  structurally. 
  

  

  It 
  is 
  most 
  interesting 
  to 
  notice 
  the 
  difference 
  between 
  

   closely 
  allied 
  species 
  with 
  regard 
  to 
  the 
  production 
  of 
  a 
  

   single 
  or 
  of 
  two 
  broods 
  a 
  year. 
  Thus 
  A. 
  tibialis, 
  one 
  of 
  the 
  

   earliest 
  spring 
  bees, 
  is 
  always 
  single-brooded, 
  while 
  its 
  very 
  

   close 
  congener, 
  bimaculata, 
  is 
  double-brooded. 
  In 
  this 
  case 
  

   the 
  spring 
  brood 
  of 
  the 
  latter 
  is 
  contemporaneous 
  with 
  the 
  

   one 
  brood 
  of 
  the 
  former. 
  Of 
  the 
  very 
  closely 
  allied 
  species 
  

   A. 
  wilkella 
  and 
  ovatula 
  the 
  former 
  is 
  single, 
  the 
  latter 
  double 
  

   brooded; 
  but 
  the 
  first 
  brood 
  of 
  the 
  ovatula 
  is, 
  as 
  a 
  rule, 
  

   decidedly 
  earlier 
  in 
  appearance 
  than 
  the 
  one 
  brood 
  of 
  the 
  

   other. 
  Many 
  of 
  our 
  earliest 
  spring 
  bees, 
  which 
  frequently 
  

   appear 
  in 
  March, 
  if 
  the 
  weather 
  be 
  at 
  all 
  warm, 
  e.g., 
  A. 
  

   praecox, 
  apicata, 
  clarkeUa 
  and 
  albicans, 
  never 
  produce 
  a 
  

   second 
  brood, 
  while 
  others 
  like 
  gwynana, 
  bimaculata, 
  

   spinigera, 
  dorsata 
  and 
  parvula 
  do 
  so 
  regularly 
  in 
  the 
  south, 
  

   and 
  when 
  they 
  are 
  parasitised 
  by 
  Nomada, 
  the 
  parasite 
  

   also 
  is 
  either 
  regularly 
  or 
  occasionally 
  double-brooded. 
  In 
  

   Northern 
  Europe 
  species 
  which 
  with 
  us, 
  even 
  in 
  the 
  extreme 
  

   south 
  of 
  England, 
  are 
  invariably 
  single-brooded 
  produce 
  a 
  

   second 
  brood 
  in 
  summer, 
  the 
  first 
  brood 
  often 
  appearing 
  

   earlier 
  than 
  our 
  one 
  brood 
  of 
  the 
  same 
  species. 
  Most 
  

   notable 
  of 
  these 
  are 
  A. 
  sericea 
  and 
  argentata, 
  which 
  appear 
  

   in 
  April, 
  the 
  former 
  even 
  in 
  March, 
  with 
  a 
  second 
  brood 
  in 
  

   June, 
  while 
  it 
  is 
  also 
  said 
  to 
  have 
  even 
  a 
  third 
  brood 
  ! 
  A 
  

   few 
  of 
  our 
  species, 
  e.g., 
  the 
  small 
  bees 
  A. 
  saundersella 
  {nana 
  

   E. 
  S.) 
  and 
  subopaca, 
  under 
  exceptional 
  conditions 
  produce 
  a 
  

   partial 
  second 
  brood 
  in 
  August. 
  

  

  Some 
  species 
  of 
  Andrena, 
  e.g., 
  carbonaria, 
  which 
  have 
  

   always 
  an 
  abundant 
  second 
  brood 
  in 
  the 
  south, 
  are 
  generally 
  

   single-brooded 
  as 
  one 
  goes 
  further 
  north. 
  Generally 
  the 
  

   specimens 
  of 
  first 
  and 
  second 
  broods 
  are 
  easily 
  distinguished 
  

   in 
  the 
  majority 
  of 
  specimens, 
  as 
  is 
  the 
  case 
  with 
  A. 
  eximia, 
  

   spinigera, 
  gwynana, 
  parvula 
  and 
  others, 
  but 
  nearly 
  alwa}^s, 
  

   in 
  the 
  9 
  sex 
  at 
  least, 
  there 
  will 
  be 
  found 
  examples 
  of 
  either 
  

   brood 
  which 
  cannot 
  be 
  distinguished 
  at 
  all 
  or 
  only 
  with 
  the 
  

   greatest 
  difficulty 
  or 
  uncertainty. 
  AVe 
  have 
  at 
  present 
  no 
  

   accurate 
  information 
  as 
  to 
  the 
  actual 
  life-history 
  of 
  any 
  of 
  

  

  TRANS. 
  ENT. 
  SOC. 
  LOND. 
  1919. 
  — 
  PARTS 
  I, 
  II. 
  (JULY) 
  Q 
  

  

  