The Garden Diary 2013

20 July - The sunshine returns for another day, it's a pleasant 18C in the garden as I write this at 8am,

and up in the Birch the caterpillar army is now divided between two leaves as morning sunlight bathes the tree canopy.

I spoke too soon this morning - soon after breakfast the clouds started to roll in and at noon there is no blue sky to be seen. The temperature was pegged to just 21C until the cloud cover started to break mid-afternoon. Even then the maximum reached was just 24C.

During the day the caterpillars remained on the one small branch,  but for some reason, left the leaf at the end of the branch only partially damaged.

It may be a coincidence, but the same thing happened on the first branch occupied by the army after its initial hatching.

It wasn't as though the leaf was completely missed, and while I watch a lone caterpillar made its way to it, went to a couple of spots where the edges had been damaged,

and then returned to the group.

It would be foolish to jump to conclusions based on that one observation, but shortly afterwards the army headed up, and not down the branch to find their next meal.

 On one leaf the army divided into two groups once more, and this time both fed at the same time - along opposite edges and from opposite sides of the leaf!

Notice on the spine of the leaf a caterpillar that is much smaller than the rest. It seems to have missed out badly in the competition for the best eating places.

This evening at 7pm the army is polishing off another leaf (circled in the photo), having already stripped this small branch of five leaves during the course of the day.

It was difficult to show them clearly in a photograph, but the red dots show the positions of the five leaves, and an arrow points to the leaf left partially eaten.

A late addition at 8.30pm - At the moment there are several places in the garden where solitary wasps are burrowing into decaying timber prior to egg laying. During the early instar stages are the caterpillars susceptible to being taken by adult solitary wasps as food supplies for their larvae?

This question is posed after I spotted a wasp investigating the caterpillars a few minutes ago. I didn't see if a caterpillar was carried away.

Unfortunately the picture isn't as sharp as it should be as I took it in too much of a rush. It also shows the caterpillars in a period of indecision before heading off to their next meal.

22 July - The hottest day so far, with the temperature under the Birch reaching 31.7C this afternoon (Farnborough recorded 32C). It seems that this record will probably be maintained for a while at least. The Jet stream flow that has passed to the south of us over the past week, and which allowed a high pressure system to envelope us has now flipped to the north of the UK. As a result, the high has been replaced by a low that will bring cooler, changeable conditions. These may well arrive with a bang tomorrow!

Anyway, today and tomorrow are more or less completely dedicated to our grandson so I have spent little time involved with the smaller occupants of the garden, apart from feeding the frogs with earthworms and introducing him to an adult harvestman which he thought was great (although he is not yet ready to touch such beasts).

The Buff-tip caterpillars continue to stay together, just about.

At one stage this morning the army was in two groups, one in disarray (seen here on the right) while the other was resting on a leaf some distance away (on a brownish tinged leaf on the left of the picture!).

This is that more organised group. It is clear that their increasing size has to make it rather difficult to achieve the level of organisation seen earlier in their development.

As far as I can tell, the majority of them are now in excess of 2cm long.

Tonight, the whole group was once again packed onto just one leaf, with close to similar numbers on both upper and lower surfaces.

23 July - We had expected today to be appreciably cooler than yesterday with a high nearer 24C. However, this afternoon it reached 29C in the garden despite a great deal of cloud cover, and after a very short shower ( thanks to a thunderstorm that missed us) it has also been very humid.

The caterpillars haven't moved since yesterday evening, and I suspect that they are about to go through their third moult.

As the pictures show, the balance of numbers between the surfaces of the leaf changed overnight. Unfortunately the crowding on the under-surface makes it impossible to do a head count.

A check on the caterpillars by torchlight at 10.15pm showed that they have hardly moved all day, a good indication that they are preparing to moult - will we see this in progress tomorrow morning?

24 July - The heatwave is over - a cool start (16C at 9am) under a covering of thin high cloud.

And up in the Birch tree, confirmation that the caterpillars' third moult is underway this morning.

In this picture you can see a couple of particularly hairy spots which highlight caterpillars that have already shed their old skins.

 At first the head capsule, and the claspers at the rear of the body, are orange and yellow in colour until the chitin hardens and darkens.

Looking closely at the cluster you can see that only a few have moulted so far. This individual, with its large, black head capsule must have been one of the first to go through the process.

In this picture you can see these two phases.

The two large lobes of the head capsule appear at first glance to be large eyes. However, unlike the adult moth (or butterfly) the caterpillar does not have compound eyes, but instead two groups of small, simple eyes.

These are more or less hidden once the head capsule has turned black, but they can be seen while it is still orange in colour.

You can see one of these groups at the bottom right of the head in this image.

By 3pm most of the caterpillars had completed their moults and a few had started to eat again,

and by 6pm it looked as though the process was complete.

The rapidly shrinking leaf was almost completely hidden by the army which now covered both surfaces.

To get a better idea of just how hairy the group was at this stage you needed to look at the leaf edge-on.

I think it give a good indication of how the group is protected from predators, with only the hard head capsules protruding as they feed on the leaf edges.

My final check of the evening was made at 9pm. By then all but one of the caterpillars had left the leaf they had moulted on (top of image) and moved down the branch to settle on four leaves.

Finally, in the way of a change, this morning I managed just a single picture of this male Gatekeeper butterfly on a Ragwort plant.

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