FAUNA AND FLORA O F MANGROVE SWAMPS
161
Similar work is now being undertaken by D. S. Kettle and his
students in East Africa.
The jetsam which marks high water mark, if wet and rotting, is the
breeding place of several species of dolichopodid, ephydrid and other
families of small flies.
1. Synchronously JEashing jireJlies
One other and most spectacular insect phenomenon deserves
mention. This is the synchronous flashing of fireflies. Buck in 1938
reviewed what was known, up to that time, about this phenomenon,
and Buck and Buck (1966, 1968) reported that it is widespread in the
eastern sector of the Indo-west-Pacific, from Thailand south to New
Guinea and New Britain.
I was introduced to this most fascinating display by Dr Ivan
Polunin, University of Singapore, who with J.-M. Bassot, Institut
Ochanographique, Paris, has been studying the behaviour of the fireflies
for some years and continues with the investigation at Benut in south
Johore and some 70 km north-west of Singapore (Bassot and Polunin,
1968). The coastal road runs within the landward fringe of the mangal,
here utilized as nypa plantations. Tidal ditches border the road. These
ditches are lined by young trees of Avicennia oficinalis, and of
Sonneratia caseolaris with an undergrowth of Acanthus ilicifolius and
coarse grasses.
As dusk gave way to darkness one became aware that certain of tha
trees were inhabited by fireflies. Exactly at what time flashing began
was not noticed but it was clear that by the time it was fully dark
many were flashing in synchrony. Buck and Buck (1966, 1968) also
mention the difficulty of establishing when the synchrony becomes
absolute. This synchronous flashing continued without interruption and
almost without variance until dawn ended the display. At least i t was
continuous from dusk till midnight and clearly seen at intervals during
a night of fitful sleep, and the insects could still be seen to flash
synchronously when it was light enough to see the insect as well as
the flash. The display is a t its most brilliant early in the evening and
as the night progresses the proportion of fireflies in synchrony usually
declines, due, a t least in part, to the elimination of copulating pairs.
Not all trees were chosen: only certain trees of Sonneratia caseolaris.
There was some spill-over on to adjacent trees of Avicennia oficinalis
and Acanthus ilicifolius but rarely on to the nypa palms. A similar
restriction to a tree of A . marina was noted at the Bako National Park
in Sarawak and to trees of S. caseolaris on the banks of the river a t
Suratthani on the east coast of peninsular Thailand. Buck records that
161
Similar work is now being undertaken by D. S. Kettle and his
students in East Africa.
The jetsam which marks high water mark, if wet and rotting, is the
breeding place of several species of dolichopodid, ephydrid and other
families of small flies.
1. Synchronously JEashing jireJlies
One other and most spectacular insect phenomenon deserves
mention. This is the synchronous flashing of fireflies. Buck in 1938
reviewed what was known, up to that time, about this phenomenon,
and Buck and Buck (1966, 1968) reported that it is widespread in the
eastern sector of the Indo-west-Pacific, from Thailand south to New
Guinea and New Britain.
I was introduced to this most fascinating display by Dr Ivan
Polunin, University of Singapore, who with J.-M. Bassot, Institut
Ochanographique, Paris, has been studying the behaviour of the fireflies
for some years and continues with the investigation at Benut in south
Johore and some 70 km north-west of Singapore (Bassot and Polunin,
1968). The coastal road runs within the landward fringe of the mangal,
here utilized as nypa plantations. Tidal ditches border the road. These
ditches are lined by young trees of Avicennia oficinalis, and of
Sonneratia caseolaris with an undergrowth of Acanthus ilicifolius and
coarse grasses.
As dusk gave way to darkness one became aware that certain of tha
trees were inhabited by fireflies. Exactly at what time flashing began
was not noticed but it was clear that by the time it was fully dark
many were flashing in synchrony. Buck and Buck (1966, 1968) also
mention the difficulty of establishing when the synchrony becomes
absolute. This synchronous flashing continued without interruption and
almost without variance until dawn ended the display. At least i t was
continuous from dusk till midnight and clearly seen at intervals during
a night of fitful sleep, and the insects could still be seen to flash
synchronously when it was light enough to see the insect as well as
the flash. The display is a t its most brilliant early in the evening and
as the night progresses the proportion of fireflies in synchrony usually
declines, due, a t least in part, to the elimination of copulating pairs.
Not all trees were chosen: only certain trees of Sonneratia caseolaris.
There was some spill-over on to adjacent trees of Avicennia oficinalis
and Acanthus ilicifolius but rarely on to the nypa palms. A similar
restriction to a tree of A . marina was noted at the Bako National Park
in Sarawak and to trees of S. caseolaris on the banks of the river a t
Suratthani on the east coast of peninsular Thailand. Buck records that