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.

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.

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.

Wolf spiders walking on water

The other day in the wildlife garden, I noticed a wolf spider, Pardosa sp., running on the pond water. I had to look closely as I had never seen them doing this and I wondered if it was a Pirate Wolf spider instead, which also live in the pond and are normally associated to water. But alas, no, it was definitely a common wolf spider like those living in my garden. She confortably moved by the water's edge, often with its front legs resting on the water surface, happily floated on the water on their hydrophobic tiptoes and easily run away very fast on it when came close.
 There is a single species of British truly aquatic spider, which live most of their lives under water, Argyroneta aquatica, the Diving Bell Spider or Aquatic Spider. The two species of Raft spiders, Dolomedes sp., one an endangered species in the UK, are semi-aquatic, and live in marshy places and hunt on water, diving if they feel in danger. Wolf Pirate spiders, Pirata sp. as I mentioned earlier, also associated to water and their protective silk tube built on sphagnum mosses ends by the water surface. All these species are unusual in which they have hydrophobic body surfaces, with short hairs that repel water and in the case of the aquatic spider, form a thin coating of air when the spider dives. Gail Stratton and her colleagues studied the locomotion behaviour or 249 American spiders of a 42 families to understand their evolutionary basis. The researchers placed the different species on water surface and recorded their movements. Some spiders sunk immediately. Other spiders which were able to float sometimes used a specialised gait, called 'rowing' which consists on keeping the first and fourth pairs of legs immobile, and moving the middle two pairs simultaneously as propellers, in a similar way to a pond skater. Some spiders able to float would walk as they would do on land. Stratton and colleagues plotted their result on a phylogenetic tree to understand if hydrophobicity and rowing behaviour have evolved just once or more times. You would naturally think that aquatic spiders have evolved their hydrophobic nature in order to be able to live in, on or near water, but in reality, they belong to a small group of spider families in which most if not all species are naturally hydrophobic, and can run - or row - on water. Two of these families, which are closely related, Pisauridae - the family to which marsh spiders belong - and Lycosidae, the wolf spiders, include many species that, although not normally associated to wet habitats, have no trouble walking on water if they need to. Hydrophobicity seems like a prerequisite for regular association to water and later semiaquatic habits.
 I wanted to check this by myself with the wolf spider living in my garden, which is likely to be Pardosa amentata, and captured an individual to test it. I placed it on a lily pad in our bath pond and it had no hesitation on walking on water and no trouble running away. In fact, it was so fast that I was unable to take a video of it doing it!

Pardosa sp. hunting on the pond of the wildlife garden 

This one is my garden spider demonstrating how its legs rest comfortably on the water surface.

More information
STRATTON, G., SUTER, R., & MILLER, P. (2004). Evolution of water surface locomotion by spiders: a comparative approach Biological Journal of the Linnean Society, 81 (1), 63-78 DOI: 10.1111/j.1095-8312.2004.00269.x