in fei Ii:
=¡2 B R I T I S H BLOOD-SUCKING FLIES
pupation the larva spins a silken cocoon to shelter the pupa, which, beingunprovided
(as a rule) with special organs of fixation, requires protection from
the current. The form of the cocoon varies greatly according to the species ;
in the British species it is usually slipper-shaped and always pointed and closed
behind, broad and open in front, with the open end facing down-stream.
From the front end of the pupa project the respiratory organs (which again
vary greatly in form according to the species) with the aid of which the pupa
extracts air from the water.* When the adult fly is fully formed, air is collected
within the pupal skin ; eventually this skin splits, the fly escapes and floats
to the surface in its bubble of air without being wetted ; the wings are instantly
unfolded and the insect flies to a nearby resting-place.
The egg-laying habits are still not well known, and certainly vary a great
deal. Probably in most species the eggs are deposited in jelly-like masses at
the edge of the water on any objects which are partly immersed ; in some
cases the females enter the water to lay, walking in along some support to a
depth of several inches, and in others it is believed that they scatter their eggs
on the surface while in flight, dipping the tail into the water each time an egg
is deposited. The eggs laid by one female number several hundreds, as many
as 350 having been counted.
Unlike midges and most mosquitoes, many Simuliidae have a considerable
range of flight. In Britain they have often been found in numbers at distances
up to two miles from their nearest breeding-place, even in calm weather.
Abroad much greater ranges than this have been noted, the greatest being in
the Anglo-Egyptian Sudan, where 5. griseicolle has been found numerous in
places as much as 200 miles distant from its home in the river Nile. Such
flights as these are doubtless largely aided by wind, but it is known to be a
habit of Si7nuliu7n to migrate from the breeding grounds in search of food,
and for the females to return later to lay their eggs.
The mouth-parts of Simuliidae, though comprising the same elements as
those of mosquitoes, are very much shorter, and their mode of action as well as
their detailed structure is quite different. The strong mandibles are formed
like a pair of scissors, the left mandible having a knob on its under surface near
the middle of the blade which fits into a socket in the right mandible, thus
forming a fulcrum, while the " handles " of the scissors are attached to the
muscles which move them. In the act of biting an initial snip in the skin of
the victim is made by the mandibles ; the maxillae, which are provided with
strong recurved teeth, are then pushed into the puncture and enlarge the
opening until it is sufficiently large and deep for the other mouthparts to be
inserted and to form a food-canal through which blood may be sucked.
The blood-sucking habit is probably common to all Simuliidae ; it has
been found that a blood-meal is essential for the reproduction of some species,
and perhaps this is true of all. Rubzov (1936) thus summarises his studies on
this point :
• There has been some dispute as to vfhether the respirator y filaments extract dissolved air f rom the
w a t e r or collect passing bubbles. Probably both processes take place, perhaps to a differing degree in
d i f f e r e n t species. Smart has found that S. ornalum can be bred in a film of water in which no bubbles
a r e present.
N E M A T O C E R A — S I M U L I I D A E
" A special search showed that for the complete development of the eggs
i f D r f n d Ru'bt^- r r f - E d w . , laupes Meig' and ^Jf.!
j r e s a ' d w a t t b e f "« f ^ ^ / k . n g and an additional nutrition with
juices and water before and after fertilisation is necessary. The fertilisation
tne lack oi food material stops their development "
Bequaert (1938) also remarks that " as yet there is no reli.bl • ,
The remar^oT Rn'h ^ attacking man as well as other mammals
biting fn t r i s :;e w L ^ f " i - ^^^
equally well the conditions in ^^ ^^ ^ ^ ^
h C ^ C t i i t r ' --iderable activity at a temperature of
¿4 -¿2 L.., with an optimum of about iQ°-?n° r tk 1, -j- r ,
All other conditions being identfca the a Hvi it- SEiSHSSSs metrical pressure has ^ p a r . L ty ^ , Ze™!"
c r d i „ „ „ y ¡„creases .he ac.vi.y J L SoodsX, H r f h r r '
.he suUry . „ r . , . c , „ „ d ^ „ „ r 3Tr e c e d t , a : f ; ° r r s . ;™^ "
. » w L ? ; : : ; : ¿' „ e ^ f r Z i i f
ba.,ks of the Danube ,„ the depa , °f Golubatz, „„ the
breeds in the r.ver Danube bemt alTo,, J" ! ? « ! " ; » . This ily
Gate, where c„„di„„„s are par iSi a ^ s ¡.ab! 1° 7'°"
years, when the level of the river fall ¡. "s a t e , ''"f »P^ent. In dry
river bed, and consequently ,„ ¡„cr ase „„r »f the
happens (as in ,9.3 L d aia „ TT '' "-¡^
breeding area oveV.he surrfu d ^ c o l . "T
partly through their own flight buf C e h thr ^ " ?? . . e c t of thetr b.tes." . / c e r ^ —