Interference patterns

One thing that I'm constantly aware of is the dramatic impact that we humans have on the wildlife that surrounds us. We cut (thrash!) hedges in summer, remove hedgerows (only to replace them with a nice fence), spray with insecticides, let our cats wander freely to bring home kills, scrape lichens off trees. And then we wonder where our wildlife is disappearing to. I like to think that I help a little by keeping some wild patches on my land, and I spend a lot of time in schools, spreading the benefits of wildlife and conservation to as many people as possible. But this year I have (albeit unwittingly) tilted the balance very much in favour of some of our local wildlife.

For many years, the Large White and Small White butterflies were not recorded in my 10k square. There are a few reasons for that, but one of the main causes is that people have stopped growing brassicas in their gardens, so the opportunity for the larvae to feed has been removed. A couple of years ago, I started a vegetable plot, but yields were bad due to very wet summers. I did notice a few Large and Small Whites, though. This year, the weather in July was superb, and the vegetable garden grew like crazy, with large leafy growth of cabbages, broccoli and cauliflower. I noticed a few eggs of Large White and watched a few of them eating some leaves at the edge of the patch, so I left them to it. September was a bit damp, so I didn't spend much time in the vegetable plot for a couple of weeks. Last week I went out to find that entire rows had been eaten back to the stalks, with dozens (maybe hundreds) of larvae on each skeletal plant, and in all stages of development from eggs to fully-grown. This is the time of year when many caterpillars seek somewhere sheltered to pupate, and the walls, windows and doors of my house are a local and acceptable place for just that purpose: this weekend, I found dozens of Large White caterpillars all round the house.

Larva of Large White butterfly ready to pupate

Having observed a large number of specimens, it seems that they choose a spot for pupation and then stay motionless for around three days before shedding their skin and making a chrysalis. I suppose this three day period is the time when the internal changes are taking place.

Successful larvae end up in a chrysalis which is usually fixed at the tail end, hanging in a head-down position:

Chrysalis of Small Tortoiseshell butterfly

I have these dangling from doors, windows, gutters, soffits and facings.

All is not rosy for some of the caterpillars, though. Large Whites have a parasitoid which is unique to them: the Braconid wasp Apanteles glomeratus. Most parasitoid wasps lay a single egg in the host's body, but Apanteles glomeratus is very small and lays many eggs inside the 1st instar caterpillar. While the caterpillar is growing, the parasitoid larvae eat the fat stores in the caterpillar, leaving all the working parts untouched. When the caterpillar has reach its final position but before it pupates, the parasitoid larvae burst out through the skin all at once:

Larvae of the Braconid wasp Apanteles glomeratus emerging from a Large White butterfly caterpillar

After a day or two, the skin blows away and we are left with a stack of pupae of the wasp:

Pupae of the wasp Apanteles glomeratus

I estimate that there are 50 - 60 pupae in that stack.

I did a rough count of pupae vs. chrysalis and I reckon 30% of caterpillars are parasitised in my sample.

Now all I have to do is keep watching those stacks to see if a hyperparasite turns up.

A completely unrelated caterpillar walked across my field of view as I was watching the Large White larvae. This is the caterpillar of the Bright-line Brown-eye moth:

Larva of Bright-line Brown-eye moth

It's interesting that the common names for moths seem to have been chosen in many different ways. I suppose early identifiers/classification experts were just as confused as we are today about which species were which, and clung to almost any clues they could get. I have identified at least:

• Habitat (e.g. Latticed Heath)
• Adult pattern (Broken-barred Carpet)
• Adult colours (Red/Green Carpet)
• Larval pattern (as in this case)
• Name of finder/identifier (Svensson's Copper Underwing)
• Food plant (Foxglove Pug)
• Whimsy (Cousin German) 
• Adult season (November Moth)
• Indecision (Uncertain)

And some I can only guess at (Vapourer).

Late update: of the most recent Large White caterpillars that I have observed to attempt pupation, 100% have been parasitised. That brings the overall total to around 80%, which is the usually-quoted percentage. A few things come to mind:

The Large White is almost continuously-brooded, since I have seen caterpillars of almost all sizes simultaneously. The parasitoid is known to be present from spring onwards, but it seems like my later caterpillars have been parasitised the most. It is also known that the parasitoid injects all of its eggs in a single injection, so it is clear that the parasitisation occurs very briefly. Perhaps the parasitoids come through in 'waves'.

I am now collecting parasitoid pupae to see how many of them have been parasitised.

Angelica time!

Angelica is one of the most important late summer nectar sources: their flowerheads are often covered in insects. Flies, hoverflies, bees, wasps, sawflies, ichneumonids, beetles and moths are often seen nectaring next to each other - mostly in harmony - but they all tend to keep a watchful eye just in case one of the sawflies gets a bit ambitious. A few spiders also lurk under the umbels and the remains of previous meals can often be seen hanging on gossamer threads.

I got a nice comparison between two identifiable ichneumonids - Amblyteles armatorius and Ichneumon extensorius - on Angelica today. Amblyteles armatorius is one of the larger parasitic wasps, at around 25 mm. long:

Amblyteles armatorius

These are parasitic on larger moths.

Ichneumon extensorius is very similarly patterned, but is much smaller, at around 15 mm. long:

Ichneumon extensorius

Sadly, the remaining 2998 or so species of our parasitic wasps need a specimen, a microscope, a reference collection and several volumes of conflicting books in order to get an identification. If I had another life, I would 'do' these.

Almost every head of Angelica has a male wasp crawling slowly over it. The males are ejected from the nest as 'excess baggage' as soon as they are ready.

Male wasp

Another frequent visitor to Angelica is the fly Sciara hemerobioides: in fact, it's the only place I've ever seen it.

Sciara hemerobioides

It took me perhaps 3-4 years to get that id: for ages I was sure it was a sawfly.

This area is on the edge of an old bog that was planted with Spruce in the 1950's. The trees were harvested about eight years ago, and some of the original vegetation is beginning to return. This is Marsh Woundwort:

Marsh Woundwort

Almost surprisingly, about 2 metres away, I found Hedge Woundwort:

Hedge Woundwort

That might explain why I have found the hybrid Woundwort - Stachys x ambigua - near here from time to time. I don't see the hybrid every year, but I suppose since the hybrid is sterile, it would need to be recreated each year.

I spotted this hoverfly and thought it was my usual Xylota segnis, but the yellow end to the abdomen intrigued me. Turns out it's Xylota sylvarum, and is new to my species list.

Xylota sylvarum

The larvae can be found in rot holes and sap runs in older trees.

The Large White butterfly was not recorded for around 12 years in my local area, but as soon as I planted some cabbage, they came flooding back. I found this batch of eggs this morning:

Eggs of Large White butterfly

Here's a close-up:

Large White eggs - close-up

Life goes on

I've been following the progress of the larvae, parasites and pupae of the Large White butterfly around my front door. Today one of the adults emerged unscathed and proceeded to inflate its wings:

It was still there five hours later.

Wood Anemones are well-named: I usually find them in woodland. Occasionally I find a few hanging on in unexpected places, which is probably an indication of what the environment must once have been like.

Some fungi are like that, too: Amanita sp. can sometimes be found in fields or hedgerows, rather than in the deciduous woodland that they normally require.

One thing that continuously amazes me is the desire and urge for species to survive. I suppose it's an essential trait for something that has lasted for millennia. This Common Dog Violet is growing in the middle of a tarred roadway. The flower is about half the normal size and the leaves are 5mm long, rather than the 25mm to 35mm that I'd expect.

This same 'survival at all costs' attitude is evident in species like leaf miners and parasitic fungi. They appear almost as soon as the leaves have opened. No time or opportunity is ever wasted.

My heart sank when I saw this Pug moth: they are the most difficult of moths to separate, I think, and I knew I was in for a while with the books. It's also very worn, but I think it's Double-Striped Pug, which I've had here a few times before.

If you think it isn't that species, then I'll be glad to fix it.

Late update: a Great Tit had the butterfly for breakfast this morning:

Like I said: Life must go on.

Spring?

Right on schedule, a male March Moth - Alsophila aescularia - came to light:

(It has to be a male: the female is wingless)

A quick check on a nearby chrysalis of the Large White butterfly shows that it has survived the attentions of both the parasitic wasp and hungry Great Tit. (Note the 'lassoo' of silk that it used to attach itself to the vertical wall, just about 1/3 of the way down from the top.)


Typha latifolia has variously been known as Reedmace and Bulrush. Seemingly, Bulrush is gaining in favour again.


If you peel back the outer layers of last year's leaves you might well notice some entry/exit holes. These belong to the Bulrush Wainscot, a moth which lives inside the plant as a larva and pupa:


It almost goes without saying that if you don't have Typha, you won't have Bulrush Wainscot moths, so they are very dependent on marshy/boggy habitat.

As I walked away from the Typha plants, I spotted this Evernia prunastri lichen on a willow:


One of the things I love about the internet is the way things link to each other, leading to unexpected connections. In May 2008, I showed the excellent mining bee Andrena cineraria.

That image was picked up by an artist living in Florida, and the resultant artwork has been shown here:

http://pencilandleaf.blogspot.com/2010/03/glamorous-grey-mining-bee.html

Isn't that wonderful?

Final results for Large White larvae

The final total of larvae (see here) that managed to succesfully pupate is 3 out of 12. So 75% parasitisation, which is well within normal parameters. Interestingly enough, the last two larvae were successful. I suppose that shows the value of having a spread of hatching/pupation dates within a species: by the time the later ones are hatching, the parasite has either died or moved on.

Sometimes it pays not to be first in the queue.

December moth and May butterfly

The first December Moth - Poecilocampa populi - for 2009. I suppose phenology has changed a bit since these were first named.



This is another first: the first of my garden Large White butterfly larvae that has survived to pupate. Of the 8 larvae that I have observed, 7 were parasitised. Now that's population control.

Four more have arrived, and we'll see what the final tally is.

My garden

The excellent Lawyer's Wig - Coprinus comatus - is a rather common mushroom: I find it on lawns, verges and rough wasteland.
It's edible, although it tends to take on the flavour of other cooking ingredients, rather than adding flavour of its own.

The other day I mused about dependent species following their host. This concept is very clearly illustrated by Apanteles glomeratus, a Braconid wasp that is parasitic on some of the 'white' butterflies. The Large White and Small White butterflies became very scarce on my local patch, presumably because people had stopped growing their own brassicas: the Large White wasn't recorded in our 10k square for 10 years. However, as soon as I started growing Broccoli 2 years ago, both species were recorded on my vegetable patch.

When they're ready to pupate, they crawl up to the eaves of buildings and overwinter in their chrysalis. They start by making a web on the upper surface, and this is the instant that disaster can strike. The larvae of Apanteles glomeratus live inside the caterpillar, eating non-essential fat deposits, using the caterpillar as a mobile food producer. The instant the web is spun, however, they burst through the larval skin and pupate for themselves. The yellow cocoons are shown below:


Approximately 60% of this year's Large White larvae appear to be parasitised, which falls within normal expectations.

So although the host was missing for 10 years, the parasite is present only two years after the host returned.