Oak Trees - Acorns _ Silk Button Galls

-

 We have 8 or 9 small English Oak trees (Quercus rober) on our land. I had a close look at them today and was pleased to see some acorns. Every 7 years or so the trees produce a bumper crop of acorns (known as a "mast year") to sate the needs of grazers so that there is a superabundance of seed and not all the acorns get eaten. (It doesn't look like a mast year this year ). The year before a mast year the trees produce very few acorns to reduce the number of grazers for the following year. Yet more evidence that trees "talk" to one another.


I looked carefully at the trees to try and find some" oak  apple" galls (round ball like structures made by wasp) and didn't find any but did find a different sort of gall one the underside of some of the leaves. These are called "Silk Button Spangle  Galls" and each one of these structures contains a developing wasp. The wasps produce chemicals that induces the leaf to form the structures.


It turns out that the wasp has an interesting and complicated life cycle. These silk button galls fall to the ground in the Autumn and continue to grow. This is an asexual (agamic) phase producing all females. The wasps continue to develop emerging in the Spring. The females then lay unfertilised eggs on new oak leaves which develop a "blister gall". This initiates the sexual stage as both males and females are produced. These lay  fertilised eggs which develop into the silk button galls.

Diary
Its been raining on and off for a couple of days. Overnight camera traps produced a couple of badger and not much else. I was supposed to be doing the last butterfly transect of the season this week but it looks as if that's not going to happen if the weather carries on as it is.



Comments

Post a Comment

Popular posts from this blog

The Dunnock

-
Image
 When I was a boy my first bird book described "hedge sparrows" but at some time in the last 50 years this name has all but disappeared and these birds are now called dunnocks (as they are not closely related to House and Tree Sparrows) Its easy to miss a dunnock! They are little brown birds and they tend to feed on the ground and keep to the cover of vegetation if they can. The males are territorial and the birds pair up in the spring. The pair are not strictly monogamous and the female will mate with another male if she gets the chance. DNA testing reveals that a brood often has more than one father. The male dunnocks are alert to this possibility and can sometimes be seen pecking at the cloacal opening of the female in an attempt to get her to expel the sperm of the competitor. The sexes look alike and these birds are common and widespread in Britain. The males get involved in feeding young according to their breeding success so it is common to find two males and one femal...
Read more

White Clawed Crayfish

-
Image
 I went for a walk yesterday that took me along the Scandal Beck (a tributary of the River Eden). On the banks of the river was a stone that had obviously been used as a picnic table by an otter and the remains of his meal were strewn about. A recognisable part of the leftovers is shown below. It's clear that this claw comes from a white clawed crayfish. These animals are not common in the UK as they need the water to be rich in calcium. This requirement is fulfilled in the Eden valley by the limestone substrate. I think that the River Eden is as far North as theses animals get. I know that there are crayfish in this part of the system because for a number of years I have volunteered with the Eden Rivers Trust to survey them. It was not uncommon to find a couple of hundred animals in a 300m stretch of river. The following images give an indication of scale. In recent years the population of the native white clawed crayfish has been threatened by the arrival of the invasive signal (...
Read more

Otters

-
 Well another Covid lockdown! As I am confined to the local area I have been having a closer look at the local wildlife. I treated myself to a trail cam and started to see what I could find. After a couple of experimental sessions to get to know the kit I set the camera along a fence line by an old railway track. On the first night I was astonished to get footage of an otter carrying a rabbit! The site is at least 500m from a watercourse which is a drainage ditch that eventually flows into a tiny tributary of the River Eden I hadn't realised that otters eat anything other than fish but apparently they do. I wonder why the otter was carrying the rabbit rather than eating it where it was found. Perhaps it was feeding young? Apparently ottters have young throughout the year. I have only seen an otter near the house once before and that was a late night encounter in the car headlights.
Read more