BIONOMICAL INVESTIGATION OP THE NORFOLK BROADS. 669 
during its existence which is supposed to last about eleven months, 
though I have reason to believe it often lasts considerably longer. 
During the nymph stage the insect feeds voraciously, in the case of 
the large thick-bodied species upon insect larvae, worms, tadpoles, 
small fishes and large Crustacea, such as Asellua and Gammarus 
and in the case of the smaller thin-bodied forms upon Entomostraca 
— I believe chiefly the Cladocera — and minute insect larvae. 
When full grown, the nymph climbs out of the water and clings 
to some support, the skin on the back of the thorax splits and the 
perfect insect emerges. The perfect insect feeds upon winged 
insects and almost certainly only lives two or three months. 
We have thus in the Dragon-fly an insect which spends the 
greater part of its life under water, and which is carnivorous in 
both its nymphal and imaginal stages. From our point of view, 
therefore, the nymph is virtually a different insect from the imago, 
living in a different element and feeding therefore upon different 
food. The swimming and walking powers of the nymph are very 
limited, and I think it is safe to conclude that its presence in any 
sub-district is satisfactory evidence of the occurrence there of the 
imago also. The reverse case, of course, will not necessarily hold, 
but, with regard to the weak-flying Dragon-flies included under 
the Zygopteridie, I think we may conclude that in the locality 
where the imago is, the nymph also lives. Of course, in either 
case it is not safe to rely upon the occurrence of one or two 
individuals as indicating local distribution ; but such records will, 
I hope, either become established in successive seasons or be shown 
to have been accidental. 
With regard to the larger Dragon-flies — the Anisopterids — I 
have, I regret to say, insufficient facts to say anything as to their 
local distribution ; the perfect insects are very swift upon the wing 
and are therefore very difficult to capture, and the nymphs are not 
always easy to find. A few facts as to the time of appearance 
and duration of life of the imagoes are worthy of our notice. 
The earliest species on the wing were Brcu’hytron praten^e and 
Libellula quadriinaciilata. These both occurred towards the end 
of May. The former was abundant at Sutton throughout June, 
although, like all the insects then about, it received a slight check 
from the frost on June 12th. After the first week in July it 
seemed to disappear. The second species persisted through July 
and was to be found in the beginning of August. 
