The Garden Diary 2013

July - part 3 

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12 July - A cool morning, with the temperature not getting into the twenties until 1pm, reaching 25C briefly around 5pm.

Caterpillar army and Shielbugs this morning, 7.30am 12 July 2013A check of the Birch around 7.30am revealed that the caterpillar army hadn't moved all night, and neither had the shieldbug nymphs.

Assuming that the nymphs are the ones that I released yesterday, there are now 27 of them, three less than before their release.

I'm writing this at 9.45pm and five minutes ago the caterpillars the caterpillars were still in the same place, not having fed since yesterday morning. The nymphs have disappeared once more!


Newly emerged micro moth (Coleophora serratella?), 12 July 2013


A long wait is over. The wandering larva that pupated on the 17th/18th June under a branch of the Birch tree (see entry for that date) has emerged as a chocolate brown coloured micro moth about 7mm long.


Newly emerged micro moth (Coleophora serratella?) - ventral view, 12 July 2013



In this image you can see the feathery nature of its wings




I'm now pretty confident that it is the micro moth Coleophora serratella. My micro moth guide (Field Guide to the Micro Moths of Great Britain and Ireland, by Sterling and Parsons) suggests several similar species that could be confused. However, only C. serratella matches the length of this moth, with the other species all being slightly smaller. Also, C. serratella is the only one that has a dark brown form, and the only one of the group that the guide says uses Birch as a food plant.

There is still one element of doubt. The guide states that C. serratella has 'Antenna with white and brown or greyish-brown bars along the inner half only'. All my pictures show the antennae of this example to be wholly ringed.




13 July - The hottest day of the year so far, with a thermometer placed on the north side of the trunk of out Birch tree and in constant shade, recorded 30. 4C (Farnborough recorded 30C at 3.20pm). With little or no breeze it has been a day for staying in the shade!

As well as being a place of shelter from the sun, the Birch has been an interesting place today for other reasons.

Shieldbug nymphs, leafhopper nymph and caterpillar on Birch leaf, 13 July 2013


First, the Shieldbug nymphs - I can no longer be sure that I'm talking about the group I released, but this morning I spotted this group of twenty nine on a branch that hangs low over the path. There have been no egg clusters anywhere along this branch or its 'tributaries' all the way back to the trunk so they must have come from another part of the tree.

They are still on the leaf this afternoon - I wonder if these too will disappear overnight.




Caterpillar under silk tunnel on Birch leaf, 13 July 2013


Anyway, the presence of those nymphs led me to this small caterpillar that had clearly been feeding on the same leaf.

In this case it was easy to see the sequence of legs expected of a caterpillar as it was upside down inside a shelter of very fine silk. This is something I shall keep an eye on over the days to come.



And another caterpillar caught my eye on an adjacent branch. It's the larva of a Grey Dagger moth and is a caterpillar that I've seen before on the Birch.

Caterpillar of Grey Dagger moth prepares to moult on Birch leaf - 1, 13 July 2013


However, today it's a bit more interesting than usual.

It is on the upper surface of a leaf and at first glance it appears to be holding on with its jaws while the rest of its body is held away from the leaf surface (although it doesn't appear to be the case in this picture the leaf is hanging almost vertically down).


Caterpillar of Grey Dagger moth prepares to moult on Birch leaf - showing silk structure, 13 July 2013



Taking a look from another angle shows that the caterpillar is being held in place by a large number of silk tethers.

At the moment the caterpillar is about 19mm long. Is it preparing to moult? My copy of 'Caterpillars of British Moths' by W J Stokoe states that the caterpillar will be feeding from August to the Autumn.



Caterpillar army on Birch leaf - mass moulting, 13 July 2013



Finally, the army of caterpillars has revealed why it hadn't moved for so long - its members were preparing to moult, a process that took most of the morning before all were transformed.




Caterpillars hang from Birch leaf during moulting, 13 July 2013

Unfortunately, as usual they were very sensitive to disturbance and with the branch in constant, if slight movement it was difficult to focus without holding the branch or the leaf.

Caterpillars undergoing a moult would hang from the leaf as seen here, but if they detected any unusual movement they would twist about. I had hoped to capture a sequence of images of this caterpillar moulting but failed miserably!



Caterpillars on Birch leaf during moult, 13 July 2013


The first and most obvious change in appearance was the size of the 'new' head. In the left-hand picture seen above the caterpillar is trying to shake off the dark exoskeleton of its 'old' head.

This can be seen here too, with the two caterpillars on the right having reached later stages in the process.



Caterpillar on Birch leaf immediately after moult, 13 July 2013



Having freed itself completely of its old exoskeleton this one moves away from the crowd under a protective cover of long hairs.




Caterpillars on Birch leaf undergo darkening after moult, 13 July 2013


The process still had some way to go for that caterpillar as it waited for its new skeleton to harden and darken.

Here, this has already taken place for a group that moulted earlier in the morning.



Caterpillars start to feed after moult completed, 13 July 2013


By the middle of the afternoon the jaws of the caterpillars had hardened enough for them to start eating again.

This time there was no mass movement to to upper side of the leaf. Instead, the first to feed simple started to nibble at the leaf edges.

They still have the instinctive reaction to disturbance, with most moving back fro the edges as soon as I took hold of the branch to steady it.



Caterpillars after moult - with scale, 13 July 2013


At this time (3pm) it seemed a good idea to record their size as the next phase in their development gets underway.

Trying to find one that remained straight was a bit of a challenge, especially as they seemed to use their claspers in a defensive posture, held up like a pair of horns, but I thing that a length of around 4.2mm (not including the claspers themselves) seems to be about right.



Meadow Brown butterfly (male) on Red Valarian, 13 July 2013



Over the last few days it would have been just perfect for butterflies, but they have been noticeable by their absence apart from a Comma which flew through the garden without stopping this morning, and this Meadow Brown male that stopped for a feed on our Red Valerian at the end of this afternoon.





14 July - As the sunshine continues today's temperature high was a few degrees lower, at 28C. but there was less of a breeze so it didn't feel much cooler. Thank goodness for the ceiling fans that we could use to direct air into the house through open windows.

The caterpillar army at noon, 14 July 2013


Just the caterpillar army to report on today as it's activities start to pick up pace. By this morning the leaf that they mounted under was all but devoured and they had moved on to another leaf lower down the branch.

This picture, taken at just before noon shows a bit of this leaf eaten.



The caterpillar army at 1.30pm, 14 July 2013


By 1.30pm the leaf has shrunk appreciably and the underside was getting crowded, but in an organised way.





Caterpillar army leaves devoured leaf, 4pm 15 July 2013



At 4pm they were on the move once more, moving down to the lowest leaves on the branch. However, that visit was relatively brief, and those leaves were left largely intact as the army beat a retreat back up the branch - this photograph taken at 5.35pm.






15 July - The hot weather is set to continue for at least the next week and today's high was 29C, with the prospect of >30C in the next few days!

Caterpillar army settles on 'new' leaf, 11.30am 15 July 2013


Overnight, the caterpillars devoured the leaf that shared the same node as the one their eggs were laid on. By the time I took my first look at around 11.30am, all apart from one stray, were now on their next meal!





Caterpillar army at rest?  12pm 15 July 2013



By the time I looked again at noon they had become organised once more around the edges of the leaf, but not yet feeding. They were nearly all in the posture adopted when moulting.




Caterpillar army feeding, 1.30pm 15 July 2013



Perhaps this was a rest period, because by 1.30pm they were feeding once more,




Caterpillars -close-up with scale, 15 July 2013


giving me a chance to find a couple of reasonably straight individuals to measure. At between 7 - 7.5mm they have not quite doubled in length in two days.




Caterpillar army leaves after eating leaf, 8pm 15 July 2013



By 8pm that leaf had no more to offer and the army was on the move one more, moving back down the branch to begin with, but by 9pm they had settled under the next leaf up the branch where they are resting as I write this.

I won't be recording their progress in as much detail from now on, apart for a 'leaves eaten' count, any other moults that they undergo, any breakdown of their organisation, and, hopefully their pupation.




A few notes about the other caterpillars I've noted over the last few days - first, the small green caterpillar spotted on the leaf with the shieldbug nymphs has disappeared. The Grey Dagger caterpillar also disappeared, although it couldn't have gone far as it reappeared this morning, now some 35mm long!

Sawfly larva on Garlic Mustard leaf, 15 July 2013

Before we went away to Cornwall (that was a long time ago!) I noted that Orange Tip butterflies were landing on Garlic Mustard plants under the Birch tree. As that plant species is a food plant for their caterpillars I have been checking for signs of them ever since, with no luck.

However, today as I checked a Garlic Mustard in a different spot I found three quite large sawfly larvae feeding on the leaves.

Sawfly larva on Garlic Mustard leaf - side view, 15 July 2013



Conveniently, this one was perched right at the leaf edge, allowing me to get a picture that shows six pairs of prolegs.






Click on images to see larger versions


2013 Garden Diary Index....  ....................... .   ..July (part 4)