Thursday, 14 June 2012

Footbridge installed

As you may already have seen, if you visit Filnore Woods, we have installed a footbridge across the muddy stream crossing at the Merry Heaven Farm end of the stream.  We have to thank South Glos council for this, especially Phil Winter their ranger, who installed it with a bit of help from Allan Burberry and myself.

The stream had spread out and made a wide boggy area

First some supporting blocks were fixed to the ground with pegs

Then the planks were attached.

Finally a handrail was added

Well done Phil and Allan (and me, Jerry!)

Thursday, 7 June 2012

Eristalis tenax

This is the Drone Fly (Eristalis tenax). It's called that because it is disguised as a honey bee drone.  You might think this hover fly was a bee but you can tell it is a fly because it only has one left wing and one right wing.  Bees and wasps and most insects other than flies have two wings on each side - four altogether. 

Drone flies hover around all summer at about head height but are completely harmless to humans.  This one died on my window sill the other day, sadly unable to get out and visit flowers in the sunshine it loves.

Notice the tiny U-shaped kink in the vein near the end of each wing.  All the Eristalis hover flies have this and a few of their close relatives.

Female Drone flies lay their eggs in stagnant water.  The larva is called the rat-tailed maggot because it has a long breathing tube like a tail to help it survive in water where there is a shortage of oxygen.  You can often catch one if you go pond-dipping.   Here are three in some water in an old tyre (not my photo)

When they pupate they crawl out of the water and find a dry place to hide.  I've never seen one of these but they are only one centimetre long and as they keep their tail they look a bit like tiny mice.

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.