THE EMPEROR DRAGONFLY, ANAX S.
IMPERATOR
BEAUFOY
T h i s , t h e largest of the British dragonflies, is widespread t h r o u g h o u t s o u t h e r n E n g l a n d a n d is to be f o u n d in small n u m b e r s in S u f f o l k . T h e writer first b e c a m e a c q u a i n t e d with it m a n y y e a r s a g o at a p o n d beside Valley R o a d , Ipswich, w h e r e a f e m a l e w a s o b s e r v e d ovipositing on the floating water weeds. T h e r e w e r e also several t o be seen over the p o n d s of the Little B l a k e n h a m chalk pits, w h e r e , it is pleasing to relate, a male w a s s e e n in 1977. T h e r e s p l e n d e n t m a l e has a blue a n d black a b d o m e n , m a k i n g it easy t o o b s e r v e as it hawks rapidly t o a n d fro a b o v e p o n d s a n d lakes in J u n e , July a n d A u g u s t . T h e green a n d b r o w n c o l o u r i n g of t h e f e m a l e m a k e s her less conspicuous. H a v i n g p a i r e d in flight in the u n i q u e m a n n e r of this o r d e r of insects, t h e O d o n a t a , the f e m a l e E m p e r o r alights on a w a t e r p l a n t , clings to it with h e r legs, a n d curves her a b d o m e n r o u n d until t h e o v i p o s i t o r is just below t h e surface of the water. M a k i n g cuts in a leaf o r stem with her ovipositor, she then inserts h e r eggs in t h e slits so f o r m e d . A f t e r t w o o r t h r e e w e e k s the eggs hatch into minute larvae with six long legs. T h e y f e e d on any living m a t t e r in the w a t e r t h a t they a r e large e n o u g h to tackle. T h e m e t h o d of feeding is p e c u l i a r to t h e larvae of dragonflies. T h e prey is slowly stalked until t h e larva is within striking ränge, w h e n it shoots out its "mask", grips t h e prey with the t o o t h e d claws at the e n d of it, a n d d r a w s t h e prey into its m o u t h . T h e so-called ' m a s k ' is a h i n g e d a p p a r a t u s , an a d a p t a t i o n of the lower jaw, which n o r m a l l y lies f o l d e d b e n e a t h the lower part of the head a n d t h o r a x , b u t which can be e x t e n d e d instantly at will. D ß r i n g the larval stage which, in t h e E m p e r o r , occupies nearly two years, t h e larva m a y shed its skin up to twelve times. A f t e r each m o u l t t h e n e w skin is c a p a b l e of a c c o m m o d a t i n g a f u r t h e r i n c r e a s e in t h e size of t h e insect. T h e cast skin is left floating in t h e w a t e r a n d is a facsimile of t h e larva, p e r f e c t a n d c o m p l e t e in e v e r y d e t a i l , e v e n to t h e claws on the f e e t , t h e covering of t h e e y e s a n d the tiny a n t e n n a e . T h e wing cases b e c o m e larger a f t e r e a c h m o u l t , finally e x t e n d i n g as far as the middle of the f o u r t h s e g m e n t of t h e a b d o m e n . W h e n t h e dragonfly is ready to e m e r g e at t h e e n d of M a y o r t h e b e g i n n i n g of J u n e , t h e larva crawls right o u t of the w a t e r on t o s o m e s u p p o r t so that the wings will be able to h a n g
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Natural History,
Vol. 17, Part 4
downwards without obstruction. Within a few minutes the skin splits behind the head and from this opening emerge the head and thorax of the dragonfly; this is followed by the withdrawal of the legs. The next twenty minutes or so constitute a period of 'rest' when the dragonfly hangs head downwards with only the end of its abdomen still held within the larval case. Then with a heave it hoists itself upright, grips the old case with its legs and immediately withdraws the end of its abdomen from the case. Again it hangs, this time head uppermost, while the small, limp and crumpled wings quickly expand to their fĂźll size. For an hour or two they will be held just apart from each o t h e r over the insect's back until they are dry and strong enough for flight. T h e r e is a pond near Reading which is much favoured by the E m p e r o r dragonfly. Many females may be seen ovipositing here in the summer months, and a mass emergence occurs at the end of May or beginning of June. Over a period of a few weeks over 4000 dragonflies may emerge, and as many as 1000 on one night at the beginning of the emergence period. The pond is about 80 yards long and 20 yards wide, shallow and pebbly at one end, and 4 - 5 feet deep and muddy at the other. It is at this deep end, fringed by trees and bushes, that the majority of the dragonflies emerge. The larvae may be seen at dusk crawling from the water up the stems of bushes and sides of trees. The emergence takes place between dusk and midnight. The perfect insects then fly away at dawn and do not return to the pond until they are mature, 10 to 14 days later. It is a wonderful sight to see by torchlight the dragonflies emerging in large numbers and then Aying away in the morning. It is easy to estimate the numbers as the empty larval cases are very conspicuous and can easily be collected and counted the following day. S. Beaufoy, M.B.E., B. Sc. (Eng.), C.Eng., F.I.E.E., F.R.P.S. 98 Tuddenham Road, Ipswich.