Page 110 - BBC Wildlife Volume 36 #10
P. 110
OURWILD WORLD
CRUSTACEANS
Whydoesahermit
crab change its shell?
Lacking a protective exoskeleton, a
A hermit crab uses the vacated shell
of a mollusc as a temporary safe house,
but must find a series of bigger homes
as it grows. Finding a shell exactly the
right size can prove difficult, and can
result in bizarre house-swap chains. If a
crab locates one that’s not the right size,
it will wait nearby until another crab
looking for a new shell arrives. When
More than 100,000 that crab sheds its old home and takes
red wood ants may live the empty shell, our first crab moves in
in each colony, creating to that newly vacated one, casting off its
a large nest with leaf
litter or pine needles. own, which is then adopted by a smaller
crab... and so on. The number of house-
swaps each crab undertakes in its life
INSECTS
varies depending on water temperature,
Which ant creates the largest nests? habitat and species. Polly Pullar
Ant hills made by the yellow meadow the size of camper vans, suggesting colony Hermit crab:
A ant, and the heaped leaf-litter nests populations of six million ants. serial house-
of wood ants, always look impressive but However, the largest colonies may be swapper.
pale into insignificance compared with those of the Argentine ant Linepithema
the subterranean cities of exotic species. humile, an invasive ‘tramp’ species native to
In Central and South America, the South America. In North America, Japan,
interconnected labyrinth of brood chambers, Australia, South Africa and Europe, where
fungus gardens (using those cut leaves as the species has been accidentally introduced,
compost) storage silos and waste storage neighbouring colonies have mingled and
facilities of leafcutter ants can reach the united to form supercolonies. The main
size of a tennis court. Experiments in which supercolony in Europe, spanning 6,000km 2
latex or plaster is poured into these tunnels, in Spain, Portugal, France and Italy, may
then excavated, have revealed structures comprise half a billion ants. Richard Jones
There might seem to BRITISH BIRDS
be too many lesser
black-backed gulls in Why are gulls of
cities, but numbers
conservation concern?
are falling nationwide.
Though urban breeding populations of
Aboth herring gull and lesser black-backed
gull seem to be increasing, numbers at rural
and coastal breeding colonies are in sharp
decline. Yet rather than simply moving from Ant nest: Alex Hyde/naturepl.com; crab: Alex Mustard/2020Vision/NPL; gull: Nick Upton/Alamy; bee: Kim Taylor/naturepl.com
coast to city, data from monitoring programmes
indicate that national populations have declined.
Herring gull numbers are thought to be at their
lowest since counts began in the late 1960s,
hence it appears on the red list of birds of
conservation concern; the lesser black-backed
gull is on the amber list. Once data from the
latest gull survey, due for completion in 2019,
are analysed we will have a better understanding
of how gull populations are changing in
different parts of their ranges. Mike Toms
110 BBC Wildlife October 2018
