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.

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