Wednesday, 24 September 2008

Ivy fest!

The end of September is the time of the year when I like to visit an old ivy growing on a south-facing brick wall. Today was the first day I saw it flowering for good. Ivy (Hedera helix) is an unusual plant in that its flowering season starts with the beginning of autumn. Given the scarcity of alternative sources or nectar at a this crucial time of the year - when many insects are getting ready for winter dormancy, egg laying or migration, this marks a food bonanza for many insects, the final feast of the year. Drone flies (Eristalis) and green and bluebottles, hover-flies, wasps, honey bees, queen bumblebees, butterflies (Red Admirals, Small Tortoishells, Painted Ladies, Large and Small Whites, Commas) buzz on the green-yellow ivy flowers.
Myathropa florea
Helophilus pendulus

Syrphus sp.

Bluebottle, Calliphora vomitoria
Eristalis tenax
Above, an illustration of the diversity of hoverflies who use Ivy

Red Admiral
And all them must keep watch for garden spiders, who never say no to a juicy hover-fly...
By the beginning of December the Ivy flowers are gone and the berries start to grow.
 This is one of the last ivy blooms of the year, with a late red admiral (photo taken 30/10/2006):

Tuesday, 23 September 2008

A bright caterpillar for a wet day

This morning walking out of the house in the drizzle, this caterpillar was curled up in the middle of the footpath.
It was large, very bright green-yellow, with a black stripe on its back. I found a plastic bottle around - a good use for litter - and put it in it until I got back home to take a photo. It was next to a fallen lime leave and I got some fresh lime leaves as a background for the photo. The result is quite nice for the strong contrast of colors.
 I wonder if it was looking for somewhere to pupate. I have seen Lime Hawkmoth caterpillars at this time of the year as limes are a common tree in my street, but it is the first time I see this species. I have put a thread in the Wild About Britain site to see if somebody helps with its ID.
 Shockingly, and brilliantly, the 'caterpillar' turned out to be a larvae of the large alder sawfly, Cimbex connatus, thanks to the WAB site for identification. WAB is a fantastic, very rewarding place to identify bugs. Usually it is a matter of hours until a discussion arises about an unidentified bug photo is posted, often involving experts in the field.
 Sawfly larvae are remarkably similar to butterfly and moth larvae - to me a great example of convergent evolution-, but they can be told apart for having a larger number of 'false legs' and other details. They are hymenopterans that lay their eggs into the tissues of plants. It turns out that this sawfly species is quite rare in the UK, with only a few records, and that it had probably fallen out of alders, next to the lime tree. Alders do not lose their leaves until late in autumn, or even early winter, so this bug had still some eating to do.
 A great find for such a wet morning.

Thursday, 18 September 2008

The end of summer

Autumn is quickly approaching. The leaves on some lime branches are already yellow and a few brown leaves rustle on the ground. The squirrels have dropped some early conkers they have nibbled. But today is a bright, warm day, with lots of butterflies. A Speckled Wood was sunning itself in the park and a Comma, a Small White and a Large White visited the garden in the morning.
We walked past one of the last buddleias in good bloom. It is now the end of the buddleia flowering season and this particular bush teems with butterflies today. I count six Red Admirals (probably already migrating south) , three Small Tortoiseshells (ready to hibernate) and a Large White.
One Small Tortoishell fed on the dandelions amongst the grass.
Other insects included a queen Bombus lapidarius, velvety black and red feeding on Agapanthus, and B. pascuorum, the most common bumblebee these days, on Sedum spectabile (below).
Lots of Araneus diadematus. One five-legged male creeps close to a female's web.
Another female nearby spins its web.
The large ivy is not flowering yet, although it's got lots of buds.

Monday, 15 September 2008

Garden Spiders

This is an illustrated account of the life cycle of the common garden spiders, Araneus diadematus, one of the most obvious invertebrate species in the September garden. The spiders have spent all summer growing and the females, now full of eggs are very large.
The spiders are born out of their silky cocoon in May and form striking spiderling balls, where all newborn spiderlings stay together in a tight 'ball'. If they are disturbed, they disperse in different directions a short distance, but regroup again shortly afterwards.

Eventually the tiny spiderlings, yellow with a triangular black mark in the abdomen, disperse and make miniature versions of their orb-web amongst the vegetation.

Males are usually darker than females and have small abdomens, whereas females have globular abdomens. Both have white marks in the shape of a cross on their abdomen. Tone can vary quite a lot, there are darker and paler individuals.

I have seen garden spiders trap and subdue a range of invertebrates, usually flying insects, from aphids to lacewings, to Eristalis flies and wasps, even butterflies. Bumblebees are strong enough to break free though.

As I have mentioned in other post, I have been lucky enough to watch the garden spider courtship in the comfort of my own home (male on the left) . The whole business took some time, and despite his apparent care, the male ended up as food for his mate (right). I don't think he managed to mate, the only contact we observed was between the front legs.

In the autumn, the female makes a silk cocoon and lays her eggs there, which is the usual overwintering stage. Here is a photo of a female who laid her eggs in a corner of the outside toilet. She stayed with the cocoon until she dissapeared (presume dead, but I never saw a body).
Something that surprises me is the range of sizes of spiders that are found in September. The larger ones surely will lay their eggs before winter arrives, but I doubt the smaller ones will. Maybe there is some overwintering of adult females in sheltered spots? I found this large specimen near the house in March.

Friday, 12 September 2008

Admirable Red Admirals

We had a clear, warm autumn morning. A Red Admiral - one of the first of a wet, cloudy summer sadly devoided of butterflies - was sunning itself on the white wall of a garage. Without a doubt my favourite butterfly. On first sight they are plain black with white and orangey-red marks, but on close inspection, the black is actually a dark brown with a beautiful iridescent sheen in fresh individuals.
The contrast and brigtness of the colours is fantastic.
But lets leave aside the looks: what makes Red Admirals amazing is that they are migratory butterflies. They arrive in the UK and Northern Europe in the spring in large numbers, reproduce there and in the autumn they return to their winter grounds in Spain and North Africa. A pretty similar migratory pattern as swallows actually. Bird migration is well known by everybody, and there is lots written about it - although until the end of the XIX, swallows were thought to hibernate under water! However, I find insect migration even more extraordinary: that butterflies, moths and dragonflies, such little things, manage to find their way across continents often crossing large expanses of water - taking into account that no experience can be used, as due to their short lives each individual is only likely to make a one-way single trip in their lives - is just plain incredible.
A paper I came across by an American team (Wikelski et al 2006) shows that progress is being made to understand insect migrations partly thanks to technological advances we could only dream about a few years ago. Researchers were able to attach miniaturized radio transmitters to the body of 14 individual dragonflies and track them during their autumn migration for up to 12 days using small airplanes and ground teams. This research showed that Green darner dragonflies follow simple migratory rules, with distinct stopover and migration days. They migrated every roughly 3 days covering over 50 km in 6 days in a generally southward direction. They migrated exclusively during the day, in days with low wind speeds, and chose to migrate only after after two nights of successively lower temperatures. Dragonfly migratory patterns and apparent strategy resemble those proposed for birds. You can watch a Green Darner fitted with the transmitter being released in the website.
Although technology is still unable to reveal such detailed knowledge on butterfly migrations, a recent paper by Brattstroem and colleagues shows that information can be gathered from visual observations of migratory butterflies crossing straits or estuaries in the same way migratory birds are recorded: red admirals crossed the sea on sunny not too windy days and flew in a direction that minimised the distance to cross over the sea.
Despite this clear evidence for migratory behaviour, recent data actually suggests that the Red Admiral is overwintering in some numbers in the UK and there seems to be a trend in which this appears to happen in increasingly northerly locations. That individuals butterflies chose not to migrate and to spend the winter and others took on the migratory strategy is also fascinating. I wonder what this rough looking one, which I found feeding on blackthorn flowers a sunny april day had been up to.

A wonderful website with lots of info on behavior, migration and research methods: Red Admirals and Painted Ladies: the Red Admiral and Painted Lady Research Site

Thursday, 11 September 2008

Daddy long legs spiders

I like having spiders at home - yes, I know, it is a bit weird and they might scare the visits. A couple of years ago we had an enormous garden spider (Araneus diadematus) in our kitchen, next to the back garden door and it eventually attracted a male. We watched the whole courtship over breakfast - live - it was fascinating. The male was extremely careful and moved slowly. A few times there was contact between the pair's legs. Unfortunately the poor male must have taken the wrong step, as the female grabbed him, and unceremoniously rolled him in a broad band of silk band and ate him. From then on we called her 'The Cannibal' and released her outside a little afterwards for her to lay eggs. I am not sure that male managed to mate before being eaten. Living on a restricted diet indoors, the female probably saw him more like food than like mate. Anyway, don't let me get distracted, I was going to talk about Daddy long legs spiders, Pholcus phalangioides, to be precise, who had lately fascinated me. If you have an outside toilet or a room next to a garden, have a look at the corners of the ceiling. You can maybe see thin 'upside down' spiders with spindly legs.
These are the spiders I am talking about. They look a bit like harvestmen, but the fact that they hang from a web tells them easily apart. Well, the spiders have lived with us for a few years, the occasional one being swallowed by the hoover. The other day I noticed one with a large prey wrapped in silk. When the spider discarded the remains I had a look and it seemed to contain a large spider, most likely a Tegenaria. Now is the time of the year when male Tegenaria move around the house - often falling into baths - and maybe it is now when they are more likely to fall prey of patient Pholcus. This is another spider capture I photographed:
Then a few days later I noticed that a Pholcus living in the outside toilet had a sac of eggs. I pulled the camera out to take some photos and, after looking at them realised that the female carries the eggs in her mouth, but they are not wrapped in a cocoon like other spiders but are visible, probably held together with a little silk. Apparently the females live for several years and can protect the eggs themselves - and possibly the spiderlings - also, because the females move to a different spot every few days, it makes sense to carry the egg sac with her.

Of course, this makes the process of spiderling hatching from their eggs visible - and relatively easy to photograph - too, and there is when I found this incredible set of photos of Pholcus spiders being born at bugguide.netAnother very informative website with good photos:

Wednesday, 10 September 2008

A digital natural history notebook?

I have taken notes about natural history on and off since I was around 12. I got my first binoculars as a present, and a new world opened before me. In more than the usual sense of being able to see things far away, as I was also shortsighted. I got my first pair of glasses shortly afterwards and the whole world become focused. Taking notes and making sketches of animals I saw, mostly birds from the local park but also reptiles or amphibians slowly become my natural history diary. I used to make the books myself, and they were monthly in my teens. I then upgraded to good quality yearly notebooks. I made line drawings and, during the summers, I had enough time on my hands to draw in them careful watercolor sketches. When faced with the need organise records to be able to go back to them I made a card file cabinet. In 2001 I got my first digital camera. With it came a new way of recording natural history sightings: even a poor quality photo is often better than your memory when trying to identify beasts. Digital photos have a date and a time, which allows for searches and immediate organisation. I then had a written notebook and photos, but little link between then. I like making my records public if they can be of any help, so, when I had to do this, it meant going through the notebooks and transferring the records onto the computer. I hope that writing a blog will be my latest upgrade in natural history recording: fully searchable and with less chances to getting lost than a precious notebook, a unique copy with all the year events. However, I am not completely sure I will stop scribbling things onto yet.