:276  ^[uintal  Rej^orf  for  U)04  of  fhe  Zoologist. 
group  of  Aphidae  as  a whole,  for  various  misconceptions  are 
yet  prevalent  with  regard  to  them,  and  not  a few  people  still 
hold  the  opinion  that  “ blight  ” is  the  product  of  a certain 
condition  of  the  atmosphere,  and  attacks  all  plants  indiscrimi- 
nately, whereas,  of  course,  every  aphis  comes  from  an  egg  or 
is  produced  alive  by  another  aphis,  and  though  a few  attack  a 
rather  wide  range  of  food  plants,  most  confine  their  ravages 
either  to  a single  plant  or  to  species  which  are  closely  allied. 
That  they  sometimes  appear  with  great  suddenness  and  in 
immense  numbers  is  true,  and  is  accounted  for  by  the  peculi- 
arities of  their  life-history. 
Aphid*,  commonlj"  known  as  green  dolphins,  plant 
lice,  blight  or  smother  fly,  belong  to  the  Order  Hemiptera, 
which  also  includes  the  scale  insects,  the  frog  hoppers,  and 
various  other  groups.  The  two  most  salient  features  of  insects 
of  this  Order  are,  first,  that  they  feed  by  sucking  and  not  by 
biting,  and  secondlj',  that  there  is  no  great  change  of  form  or 
“ transformation  ” as  the  young  insect  grows  to  maturity. 
They  never  exist  as  grubs  or  maggots,  but  the  newly  hatched 
young  is  from  the  first  not  greatly  unlike  its  parent. 
Perhaps  the  most  curious  point  about  the  Aphid*  is  that 
the  male  insect  is  rarely  met  with,  and  in  the  case  of  many 
species  has  never  yet  been  discovered  at  all.  In  those  cases 
where  the  males  are  known  they  ajjpear,  as  a rule,  only  for  a 
short  time  during  the  autumn.  Probably  the  most  usual  life- 
cycle  is  this.  In  autumn  males  and  females  appear,  and  the 
latter  lay  eggs  which  do  not  hatch  till  the  following  spring, 
when  they  give  rise  to  wingless  females  which  straightway 
begin  to  produce  living  young.  These  are  all  females  which 
in  their  turn  verj"  soon  become  adult  and  have  broods  of  their 
own,  and  if  the  circumstances  are  favourable  in  a wonderfully 
short  time  the  plant  on  which  they  are  feeding  will  be 
smothered  by  myriads  of  wingless  female  aphids  without  a 
male  among  them.  Obviously  there  is  a limit  to  this  j)roceed- 
ing,  for  with  the  failure  of  the  plant  starvation  would  ensue 
to  these  inert  wingless  creatures  which  have  no  atle(juate 
means  of  migration.  Unfortunately  for  the  agriculturist  this 
contingency  is  only  too  efficiently  provided  against.  As  soon 
as  the  plant  is  in  danger  of  being  inconveniently  crowded 
many  of  the  young  aphids  begin  to  grow  wings,  and  these 
winged  females  serve  to  spread  the  attack,  having  the  instinct 
to  seek  out  the  proper  food  plant;  and  it  is  noteworthy  that 
scarcity  or  poverty  of  food  seems  to  stimulate  the  young  insects 
to  form  wings,  for  these  winged  forms  do  not  occur  with  any 
regularity,  but  are  sure  to  be  found  when  the  aphids  begin  to 
be  overcrowded  or  the  plant  fails  to  afford  them  sufficient  sap. 
Thus  throughout  the  summer  there  are  several  successive 
