Wednesday, 23 July 2014

Insects in flight

Today it was a summery, hot day, with a light breeze, ideal for insect watching. Somehow, I managed a few decent in flight shots, which usually evade me as I am not patient enough. The first one happened when I spotted two hovering Volucella pellucens. They are large hoverflies, which live near trees and are identifiable even at several meters of distance due to their translucent abdominal belt. Males hover incessantly on the same spot, and inspect or chase off other hoverflies and even speckled woods invading their territory, so maybe this way they spot female hoverflies to mate. Hoverflies also hover during courtship. I tried to encourage the hoverfly to sit on my finger by slowly raising it towards the hoverfly. This technique often works with hovering males, like this Eristalis intricarius from yestarday shows:
but the Volucella refused several times...
so I tried to get some shots while it hovered and got the shot at the top of the post, and I was pretty pleased with that!
 A bit later, then, in my street, a couple of migrant hawkers were hunting over the verge. Migrant hawkers often hunt together with other individuals, and they may settle to bask near each other. They ten to hunt from 4-5 m above ground. I managed some records shots, this one the best.
I popped in the wildlife garden later to release a grasshopper (a matter for a different post) and watched a large Ectemnius digger wasp (probably the common E. cavifrons) inspecting a rotten log. She had to fend off a Tegenaria spider. Ectemnius are hoverfly hunters and are skillful hovers. Females dig their nests in soft wood, and look by suitable nest sites, often hovering in front of the wood. This allowed me an opportunity for the third flight shot for the day.

Saturday, 19 July 2014

Nursery web spiders and their nurseries

The population of nursery spiders at the wildlife garden is particularly obvious now, as their nursery tents hang from their high positions from grasses and meadow cranesbill leaves, closely guarded by females. There are at least 20 nurseries scattered over the meadow at different stages of development. In some the spiderlings have already dispersed, after spending a few days safe inside their tents. This is what W.S. Bristowe had to say about the female after mating takes place:
During the first half of June the female may be see trundling along with a huge light-coloured egg sac under her sternum which is attached to her spinnerets by threads and is held in her chelicerae. At about the time the eggs are beginning to hatch, she loosens the outer covering and attaches it to a blade of grass. The she weaves a tent over it on the outside of which she stands on guard [...] The young emerge in late June or early July, after moulting once inside the egg sac. Now they cluster together in a ball inside the tent for a few days before moulting for a second time and dispersing.
I found the first nursery with already emerged spiderlings on the 20th of June. Bristowe was of the opinion that Pisaura will have two batches of eggs. Although the female below was carrying an egg sac on the 4th of July, I am not sure if this represents variation on the date of reproduction of different individuals as they mature, or evidence of a second batch.
Female carrying her disproportionate egg sac. They appear to walk on tiptoes holding it. I don't think the female is able to hunt while carrying her egg sac.
This spider has a fresh nursery web and appears to be manipulating the egg sac to allow the spiderlings to emerge.
Unlike the neat, smooth new tents holding clustered spiderlings the tent above has a few holes (made by the female?) allowing spiderlings to disperse. The spiderlings are clustered forming a ball just visible at the top right hand corner of the nursery tent.
The spiderlings are often clustered together in a ball like garden spider ones. The ones above look like they are ready to leave their tent.
If you click to enlarge the photo you might be able to see some tiny spiderlings on top of the tent already leaving.
I haven't found any information as to the function of the nursery web. Certainly it keeps the spiderlings dry during rain, and the mother is often found underneath also during poor weather. It could offer protection from parasites or predators. Many predatory insects will readily take spiderlings, including wasps, and it appears that the nursery web is not totally wasp-proof, as these photos on Flickr show.


Friday, 18 July 2014

The burnished bronze bug

This is not the common name of this large shield bug, Pentatoma rufipes, which actually goes by Forest or Red-legged Shieldbug, but it should be. I found the individual above todaty on a pavement today and had a plastic pot at hand to bring it home and give it the white bowl treatment to bring out its colours. This shiny, metallic beauty becomes an adult at the end of June or July, as the photo below of a teneral adult, just moulted out of its also shiny last instar nymph skin shows. Even when the full colours are not evident, the prominent 'shoulders' are characteristic.
Teneral Forest Bug

Large shieldbugs are relatively easy to identify, even at their nymphal stages. The British Bugs site is always good starting point.

Saturday, 12 July 2014

Watching Pirate wolf spiders

I went to the wildlife garden with the intention of watching some wolf pirate spiders. These are spiders that often walk on water and are found in close association to wet habitats. They are wolf spiders and, although they make a silk retreat, they do not make a web for hunting, instead relying on an ambush strategy to capture prey. The species in the pond most resembles Pirata piraticus, the most common species. These spiders are found as adults from May to September.
 I sat by the edge of the pond, and was entertained by several pond skaters squabbling for a dead mirid bug.
But it wasn't long when I spotted a male pirate wolf. I took a photo, but he rapidly disappeared in the thick vegetation of the pond. These spiders have a very characteristic coluration, with a whhite edge around their thorax and abdomen and a background rich brown and greenish, with unpatterned legs. Males have paired white spots on the abdomen, while females also have a white V shaped mark around the middle of her abdomen.
Another smaller individual, also a male, crossed the pond rapidly. In a cursory view they do look remarkably like pond skaters, specially due to the pale fringe of the abdomen and the way they move on the water...
...but he crossed the pond again and I lost it too.
Then I spotted another one. This one looked quite shy and reluctant to move, and it sat hidden by the stems on the water edge.
 I got closer and gently enticed it to come out (top shot and below) and then it become obvious that she was carrying a large, white egg sac.
It then become obvious why the white stripes, these are very similar to the reflections of the water on the edge of the pond, and probably help concealing the spider to their predators, and possibly their victims.

A Stretch spider by the pond

I spent some time in the wildlife garden this morning looking and photographing pirate wolf spiders (post to follow) and watching pond skaters in the pond. I had noticed a pair of legs coming from under a yellow flag leaf, hugging it and I decided to inspect. As I turned the leaf I spied a large, wonderful female stretch spider of the genus Tetragnatha. The spider had its front and rear legs stretched to the front and rear, and held onto the leaf with her middle legs. She walked up and down the leaf, rearranging her silk threads, which I had possibly dislodged. She was quite a large sized and very colourful spider, with yellow and red stripes on her elongated abdomen, it looked so exotic and tropical!
  Out of the six British species of Tetragnatha, two are larger and more common and one of them associates with water, T. extensa, although detailed genital examination is needed for a secure identification.
 Tetragnatha have very large jaws, and the males using their modified jaws to lock the female's in place - and keep out of danger - when mating.
 You can see the folded fangs in this shot
And this is a scanned figure from Bristowe's The World of Spiders (1958), drawn by Arthur Smith, demonstrating the locking mechanism (male at the bottom)





I took this shot to give you an idea of the size of the spider

For a wonderful account of the mating behaviour and natural history of these spiders, go to the Spiderbytes blog.