September issue - Magazine - Page 33
LOCAL INTEREST
Nature Notes
Sheena studies some strange parasites while Jackie bids farewell to the Swallows
Now that the leaves are falling from the trees it's easier to see
and appreciate those strange growths that often appear on
branches and twigs – the so-called galls.
Galls are growths on plant tissue caused by a number of
different parasites. They can develop because of insect or fungal
activity or by the plant becoming infected by viruses or
bacteria. The overgrowth of cells that results from these
invasions doesn't harm the overall health of the tree but, unlike
other forms of parasitic relationships, it doesn't bring the
vegetation any form of advantage or benefit either.
Even if science had identified every one of the different
insects and infections that can cause a gall to form - which it
hasn't - it would be difficult to find the space to name them all.
In fact, the British Plant Gall Society lists 1,436 what they call
identified 'causers' of plant galls. One thousand and three of
those are insects, including various sorts of flies, midges,
weevils, wasps, aphids, sawflies and moths, and 331 are types
of fungi. Numbers to make your head spin!
There are a handful of notable galls that we do know about,
and they are quite common if you keep your eyes peeled. One is
the Oak Apple Gall that tends to appear
on the sessile (Cornish or Irish) oak. It is
caused by a gall wasp called Biorhiza
pallida that lays its eggs inside a dormant
leaf bud. When the larvae hatch in spring
they trigger the formation of galls. After
they take to the wing most of the galls will drop off, but some
remain and become very woody. You'll see these in autumn.
Then there are Oak Marble Galls that come
from another gall wasp, Andricus kollari,
introduced from the Mediterranean in the 1800s
because its galls have a high tannin content,
which made them useful for tanning leather and
dyeing cloth. Oak marbles are found on
pedunculate (or English) oaks where the wasp
larvae are protected from the elements by the
tannins and the galls' woody outer shell.
The Knopper Gall has not long been seen in the UK as the
wasp, Andricus quercuscalicis, only arrived here
in the 1950s. It lays its eggs on the freshly
pollinated flowers of the English oak, causing the
acorns to deform and drop in the autumn. Search
the ground round an oak to find these.
Leaving oak galls to one side, the Bedeguar Gall,
nicknamed Robin's pin-cushion, is
commonly found on dog rose,
sweet-briar and field roses, especially
when we've had a hot, dry summer
like this year. There are five rose gall
wasps in the UK but the bedeguar
gall is caused by Diplolepis rosae.
Each gall contains many wasp larvae, each in their own
chamber, which they will leave in spring. The galls should be
full sized by now and will be very obvious.
Even smaller, Lime Nail Galls
are caused by a mite that feeds from
the new leaves of lime trees in spring,
causing growths like pouches to form.
Later in the year, when the pouches
are partly formed, the mite lays her
eggs inside. The larvae live in the galls until late summer, but
the galls themselves remain on the leaves until they drop in
autumn. Search for these on the ground around lime trees.
The Tongues of Fire Galls are
caused by two species of rust from the
Gymnosporangium genus and you can
find them on hawthorns and junipers.
The 'tongues' are known as telia and
they produce spores which are released
on the wind to find new hosts. Ordinarily,
the gall looks brown and wrinkly but
when it rains the telia swell and turn orange, giving them their
apt name.
BYTHAM BIRDS
It was apparently Aristotle who said, 'One Swallow does not a
summer make.' Clever man, Aristotle. So, my question is, do no
Swallows mean it's winter?
We have just returned from a birding trip to the Scilly Isles.
When we arrived there were simply clouds of Swallows
everywhere. Over the ponds, swooping low over the fields
catching insects and, most surprisingly, feeding at zero altitude
over the beach tidelines where due to recent storms there were
piles of seaweed.
Locally Swallows have done well this year and there have
been many in our sky all summer, but the numbers on Scilly
were simply staggering. Then, after five days of enjoying their
company, suddenly they were not there, just an odd one or two.
When we returned home there was not a single Swallow or
House Martin to be seen. Of course, the explanation is simple.
These insect-eating birds do not stay with us over winter, they
cannot possibly find enough food. Therefore, in common with
many other bird species, they migrate to warmer climes where
insect food is plentiful. The Swallows on Scilly were simply
using the islands as a service station, stopping off on their
southerly flight to feed up before setting off for the long
foodless passage over the ocean.
So that is it now. We shall not see another Swallow until
next April. (Is that summer? Aristotle did not think so.) The
Swifts went even earlier and will not return until May. Our
Swift nest boxes fledged at least two young. One day they were
not peeping out and had simply dropped out of the nest box,
learning to fly in less than a second. They will not land again
until they are ready to breed in two or three years' time. Then
instinct will bring them back to our house, in the same way the
Swallows and House Martins will return to their natal site.
We can do a lot to be ready to welcome their return, making
sure the garden has plenty of nectar-producing plants to feed
insects, and therefore birds. British native plants are best. Do
not use chemicals of any sort (why anyone would wish to kill
insects is quite astonishing to me). Leave existing Swallow and
Martin nests alone - they do no harm, and would you like to
rebuild your house every time you returned from holiday?
Lastly, if you have no nesting birds (of any species)
consider putting up nest boxes. Pre-formed Swallow and martin
cup nests can be purchased and next year Pete and I will have
more Swift boxes available if you have a suitable location.
Page 33
Knopper gall by Njarvis5; Robin’s pin cushion Sarah Lisette Hague; Tongues of Fire gall Jason Ondreicka; Lime Nail gall Christian Weiß; Oak Marble gall Anders93; Oak Apple gall Thomas Males; Swallows Iurii Pozdnikov| all Dreamstime.com
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