Tuesday, May 07, 2013

The ash and the ants

A colony of wrinkled ants, Myrmica ruginodis, has appeared under the Lyon Stone.  Much later than usual and normally by this time of year there are several large colonies.

This evening I spotted two individuals that had climbed to the top of the ash tree, now just over a metre tall, and were browsing eagerly on the tiny glandular hairs that cover the new leaf stalks and petioles.


Such attractions are known as 'extra-floral nectaries' (EFNs) as they are not associated with flowers and they occur on quite a wide range of plants (including narrow-leaved vetch in the Square Metre).

The hairs produce a sweet material containing various sugars and other substances and are clearly both tasty and nourishing as far as the ants are concerned.  What advantage the plant gains is not clear, but is has been suggested that the ants discourage other insects and herbivores both of which might damage the plant (I find that unconvincing).

Like others with ash trees I am scrutinising our Metre plant regularly for ash die back disease, but it seems fine so far.  However, as spores of the die back fungus are dispersed from fallen leaf stalks of the tree, ants might well unwittingly transport them from the ground to the most vulnerable parts of the plants.


Note the ant on the left of the above picture of the terminal shoot of our tree.