Monday, 4 June 2012

Oak apples

This is an extraordinary year for oak apples.  It must have been a milder winter than usual.  Lots of oak trees at Filnore look like crab apple trees fruiting early. 


Boys and girls
Actually, of course,they are not fruits at all but galls produced by the tree when a particular tiny gall wasp called Biorhyza pallida lays its eggs.  In July the galls mostly fall on to the ground and up to 100 tiny insects either males or females emerge from each gall.  After mating with an elgible male, the females fly to the roots of an oak tree and lay eggs into the fine roots just under the soil.  

Winter brood  
This makes the tree produce soft pink galls on the roots for the grubs to feed on.  All these grubs turn into wingless females, looking like tiny ants about 5mm long.  In December they pop out of the galls and climb into the branches of the oak tree to lay their eggs in the buds.  It takes them up to three hours to lay 100 eggs.  All this in the depths of winter.  Such determination. 

Truly a life cycle
These are the eggs that cause the oak apples in April and May, to complete the circle by producing the winged males and females in July.  What a business.

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