28 May 2011

A lonely bird's-nest orchid

On a walk I was leading in Brede High Woods today, we came across one spike of the strange bird's-nest orchid (Neottia nidus-avis), a plant I have never seen in this part of East Sussex before.  It was in an area of shady chestnut coppice in a place where there is large number of twayblade orchids (Neottia ovata).

20110528 BHW Neottia nidus-avis 001

The twayblade has recently been moved to the genus Neottia, so both plants may like similar conditions.  I suspect they prefer places in Brede High Woods where there is a particularly high lime content in the soil, perhaps due to some earlier human activity.

The bird's-nest orchid is myco-heterotrophic, meaning the roots of the orchid draw nourishment from subterranean fungal mycorrhiza and not from decaying wood and other vegetable material as was once thought.  None of the plant contains any chlorophyll.

20110528 BHW Neottia nidus-avis 004

Since the turn of the century this species has vanished from many of its East Sussex locations and is now most often found in beech woods on the Downs, especially in West Sussex.  It also is said to prefer wet springs, so it seems that we were lucky to find it in this exceptionally dry season.

22 May 2011

Balfour's bramble & small black ants

The earliest of the blackberries  to flower, Balfour's bramble (Rubus nemorosus) is now showing well under the transmission lines across the eastern part of the woods and elsewhere.

BHW SV 046

This used to be known as Rubus balfourianus, hence the title above and is one of the innumerable microspecies of bramble.  It has very distinctive large, flat flowers attractive to a wide range of late spring insects.  In his book on British Rubi, W. C. R. Watson (1958) says this species prefers damp, often clayey, places and that the fruit have a mulberry flavour.

Also close to the transmission line on the sandy top of the root plate of a fallen tree, I found a few small black ants (Lasius niger)patrolling rather slowly and seemingly aimlessly about. 

Roughly half of them were carrying something

20110517 BHW Lasius niger carrying live worker

which turned out to be another small black ant worker with tightly curled, legs and antennae tucked in and positionedon its back.  At first I thought this was some sort of predator and prey episode, or that the carried ant might be a corpse.  But when I nudged a pair into a tube, they separated and both seemed in perfectly good health.

The literature says that this species and other ants often do this, but I have read no very convincing explanation as to why.  The most popular theory seems to be that the ants are moving from one nest to another and, for some reason, some of the workers need to be carried.  Perhaps they have a special role that makes them weak and lazy.

18 May 2011

More records of rare insects

In recent weeks friends like Dave Monk and Colin Boyd have taken some stunning photos of hitherto unrecorded, and often very scarce, insects in Brede High Wood.

In bluebell time Dave Monk photographed a little moth called the bluebell conch (Hysterophora maculosana).

H. maculosana DSCN65~3a

The caterpillars of this species feed on seeds of bluebell and, whilst it may be widespread where bluebells are abundant, it has rarely been recorded in Sussex.  It is, I think, a good example of the balance of nature.  Although there may be apparently inexhaustible supplies of its food plant (from the moth's perspective), it does not appear to have any significant impact on bluebell populations: it simply takes a modest helping of the available bounty.  Pity Homo sapiens doesn't do the same.

The picture above, by the way, is the only one I can find with the moth on a bluebell.

Colin Boyd has been making many hoverfly discoveries.  The picture below is one of his of the hive bee mimic Criorhina asilica.

P1080982 Criorhina asilica BHW

The larvae of this species develop in rotten wood with a preference for ancient woodland sites and this highlights the importance, enshrined in Woodland Trust policy, of conserving dead wood as well as living trees.

The photo below, by Dave Monk, is of an ant beetle or checkered beetle (Thanasimus formicarius)


This is a predatory species also associated with dead and dying trees, both coniferous and broadleaved.  The adults prey on the adults of bark beetles (Scolytidae) while the larvae eat the larvae of the bark beetles.

In Sussex the species has been recorded mainly from ancient parks and woods in the west but also from Eridge Old Park in East Sussex.

The adult beetles have a marked resemblance to the large velvet ant (Mutilla europaea) - Google it and you will see what I mean - a species with a formidable sting and therefore one might hypothesise that the colour and pattern is a protective device in the beetle.  However, the velvet ant seems to be so rare, nowadays at least, that any would be predator is unlikely to be familiar with its appearance  (Mutilla has never been recorded from our part of East Sussex so far as I know).  Perhaps the pattern on the beetle activates some atavistic repulsion mechanism in the brain of the insectivore.