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Glow-worm Lampyris noctiluca
By Roger Tabor, Chairman of The British
Naturalists’ Association
The British Naturalists’ Association has
a particularly close connection with this beetle, for it was
this Association that carried out the UK’s first National
Survey of Glow-worms during the 1970s. This was carried out
by the late Anthony Wootton, as editor in ‘Country-side’ magazine,
the journal of the BNA. He encouraged members to send him
records of sightings of Glow-worms, both then current and
old records.
These were published in Country-side magazine,
initial findings in 1971 (21, 456-463 and 572-574), and then
in complete form in the Spring issue in 1974 (22, No. 6, 266-271).
BNA
Glow-worm Survey from 1974
One finding was of the large number of
Glow-worm populations found on railway cuttings and embankments.
The distribution map published in Country-side showed a far
greater number of reports from Southern England. The current
national Glow-worm survey that began in 1990 is organised
by Robin Scagell, and it developed from the BNA findings as
its core, which it acknowledges. Other surveys have continued
to gather sightings, notably the Essex Glow-worm Survey published
in 2001, resulting from a systematic survey by Tim Gardiner,
Michelle Pye and Robin Field.
Alfred Leutscher, a celebrated former
Chairman of The British Naturalists’ Association, writing
in 1974 (in his book ‘Epping Forest - its History and Wildlife’),
recalled the camping days of his youth in Epping Forest when
Glow-worms were so plentiful some were gathered and put in
jam-jars hanging in the tents to provide a light which was
sufficient to read by. That evokes a by-gone era of the 1930s
and before of wild nature and abundance, but Glow-worms now
have become generally recognised as ‘rare’.
Glow-worms are not worms but beetles,
and the reason for the mis-name is that it is the female that
strongly glows from the last 3 segments of her body, but unlike
the male she has no wing cases so at a quick glance could
be confused with a larvae. However, the adult legs should
dispel that assumption.
They stay fairly localised during the
mating season, to a traditionally used site, so naturalists
can return year after year to monitor the site. As the females
only ‘switch on’ their light at certain times, they are far
less conspicuous during most of the day, more hidden from
predators. She ‘switches on’ to attract the flying males,
but if at any point of her signals she is disturbed, she can
switch off and disappear again.
The cold light is produced as bioluminescence
when an enzyme, luciferase, enables the oxidation of luciferin
which gives oxyluciferin and the light.
They can be found by walking within 2
hours after dusk in expected areas from June until mid-August
(and even early September) but mid-July is the most likely
time. If you are one of the observers in the original BNA
National Glow-worm Survey it would be very helpful if you
could check, or arrange to have checked, the site where you
recorded them and informing the BNA (science@bna-naturalists.org)
if they can still be found.
The female Glow-worm normally blinks off
its light briefly for a few seconds, and then back on, but
sometimes the light is sustained. The adult females don’t
feed, so die after a few weeks, normally following laying
eggs. After about a month those eggs become larvae that voraciously
feed on small snails. The larvae inject a liquid that contains
digestive enzymes that turns the inside of a snail into a
soup that the larvae suck up.
Limestone or chalky soils are best for
snails, as they provide calcium for their shell formation,
consequently such areas are better for their predators, the
Glow-worm larvae. I well remember walking along a path at
Barnack Hills and Holes, an area of mounds, remnants of historic
limestone quarrying, and meeting one on the path! I was being
filmed for my Anglia TV series ‘Going Wild’, and I had hoped
to find a Glow-worm larvae, but thought I was being optimistic.
Instead the Glow-worm found me, and without breaking its step
obligingly crawled on up my proffered finger and into ‘Glow-worm
TV-stardom’! This one was quite large, and they can be up
to around 25mm long when big. That is the same size that an
adult female can be (15-25mm), with the males being a bit
smaller (15-18mm).
Glow-worms appreciate open grassland of
the type found at Barnack Hills and Holes, usually not overgrown
by other plants, and with grass stems that the females can
climb up and while clinging on, rotate the end of their bodies
so that the light of the last 3 segments can be seen by flying
males.
I monitored one site in a small Essex
lane over a number of years which had, at its height, 14 glowing
females. They were on both sides of the unilluminated road.
It has been down to half a dozen in some years. The length
of useable lane by the Glow-worms was reduced by the arrival
of a bright light source around the corner, which brought
the number down by 3. The most significant single damaging
event was that a huge lorry drove the full length of the verge
on the flat verge. As all of the population was within the
first foot of the tarmac edge, it was not surprising that
none were seen the following year. The steeper sloped other
verge was protected from such damage by its shape.
However, nationally the dramatic increase
in lighting from streetlights to shopping areas and housing
has implications for Glow-worms. For example, in the county-wide
Essex Glow-worm survey of 2001, 78% of glowing females were
recorded from unlit sites. The gentle lights of the Glow-worm’s
love-life cannot compete with our present day massive light
pollution.
© Roger Tabor 2006
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