Monday, 9 July 2018

Last orders please …

Purple Emperor (Apatura iris)

Knepp Estate, West Sussex (5th and 6th July 2018)






The 2018 Purple Emperor season has all but come to an end. My first sighting this season came on Tuesday, 17th June, with several sightings in the traditional areas of Chiddingfold Forest, Surrey. The first Sussex specimens appearing a few days earlier.

The varied and sometimes rather offensive feeding behaviour of iris has always fascinated me. Putting aside the rather unpleasant nature of male table manners, both male and female iris will travel some distance to major sap runs on trees.

A tree, by its very nature, is a closed hydraulic system. Water rises up through the tree in the outer edge of the woody material; the xylem. The water, which is called sap, is a solution of mineral salts that have been absorbed from the soil. The sap is enriched with sugars being transported from storage in the roots to the shoots where they are used to provide energy necessary for shoot growth and leaf expansion. Once there is positive water pressure in the tree, damage to the tree may release the pressure and allow sap [usually a colourless watery liquid] to escape and the tree will 'bleed'. Alcoholic flux is a stress-related disease. It usually occurs after a period of very hot, dry weather. The disease is caused by a microorganism that ferments the sap that seeps or bleeds from cracks and wounds in the bark. The result is a white, frothy ooze that has a sweet, fermenting odour similar to beer. Anyone who has ever sugared for moths will know how effective a mix of molasses and beer can be in attracting a host of insect species; the odour of fermenting sap having a similar appeal.

The above images show iris feeding on several oak sap runs high in the canopy.

More at:

Patch, D. (2004). Trees Bleeding. Trees in Focus, Arboricultural Practice Notes (APN 8). Farnham: Arboricultural Advisory and Information Service.

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