Sunday, 29 June 2014

Wolf spiders walking on water

ResearchBlogging.orgThe 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

Monday, 23 June 2014

Wildlife Garden little wonders

It is National Insect Week! To celebrate I popped down to Pearson Park Wildlife Garden, one of my favourite haunts, and a biodiversity hotspot in the heart of Hull. In a sunny, summer day, insects and other invertebrates are guaranteed and there are always some surprises. I walked around the garden, following a male Brimstone, but it refused to settle. Several other butterflies were around though. In a sunny, sheltered corner in a wooded area, two Specked Woods whirled around each other. The territory owner, looking quite battered but still going strong, settled on a bramble leaf (above).
 Bobbing up and down through the long grass, two Ringlets were chasing and courting. The female appeared to reject the male (on the left), and he flew away.
Ringlet resting (This photo is from Sunday)
There were two male Common Blues chasing. Afterwards, this one settled on birds foot trefoil to groom.
This green lacewing, Chrysopa perla, looks like is ready to lay her eggs.
The meadow cranesbills are in full bloom, attracting plenty of insects, like this small hoverfly, Sphaerophoria scripta... hovering in front of a flower
On the buddlejas there are many Green Shieldbugs, Palomena prasina, the female is on the right. 
And just by them a soldier fly
A tree stump used as a bird table gives provides suitable nesting sites for these Crossocerus wasps and others.
The pond had me entertained for quite a while. I sat down on the shore and watched. This Azure Damselfy was doing some impressive morning stretches, up!
and down! There were two males and a mating couple.
One of many pond skaters
Just by the water edge, this wolf spider carrying young was trying to find a sun fleck to bask. Several seemingly common wolf spiders Pardosa sp. fed by the water's edge. Some even crossed the water running fast over it.
The water's edge was teeming with Amber Snails, Succinea putris, feeding on wilted leaves
Although there are plenty of Harlequins, 7 spots (above) and 14 spots were also about
I found this female Nursery Web Spider guarding her nursery on the nettle patch at the end of the vegetable garden. There were many spiderlings inside, and some still appeared to be coming out of their egg sac.
This is the cocoon of a burnet moth, which shall emerge in the next few weeks in the wildlife garden.

Thursday, 19 June 2014

Mouse spider nest

As I checked the bee hotel, the Mouse Spider, Scotophaeus blackwalli, was looking considerably thinner than last time I checked. And lo and behold! She was guarding a fresh, pure white silky cocoon holding her eggs in a neat bundle. I will update this posts with further developments.

UPDATE 9th July. The female is still sitting right on top of the egg sac.

Friday, 13 June 2014

Rosemary Beetles

For a few years I had expected the arrival of this brightly colourful leaf beetle to my garden. It has followed its food plants, which include not only Rosemary but Lavender, Sage, Thyme and related aromatic plants. As other species accidentally introduced in a non-native range, it has expanded quickly in the UK from its presumably initial introduction point at an RHS garden in Surrey in 1994. By 2005 it had spread throughout greater London and nowadays it has spread north to Scotland (see the NBN Gateway map here).
 Today, four adults were feeding on a single lavender plant in the garden. I couldn't see any others in the other lavenders, so I wondered if they were the offspring of last year arrival.
 The adult and larvae feed on leaves and flower buds and they can quickly defoliate bushes as the summer progresses.

More information
RHS page on Rosemary Beetle.

Wednesday, 11 June 2014

Red Admiral showing and hiding

 A fresh female Red Admiral basked on a sycamore trunk, probably with a full stomach after feeding on an early flowering buddleja nearby. It sat there wings outstretched, showing its bright, contrasting colours for a while, but then it decided it had enough and folded them, revealing its remarkably cryptic underside.

Monday, 9 June 2014

Spider eggs and egg sacs

Spiders make remarkable mothers. One of the most widespread maternal behaviours is the more or less elaborate construction of an egg sac, and many species are making them at this time of the year. The mother wraps a batch of eggs - which might be the only one she will produce during her lifetime - into a neat parcel kept together with silk. The egg sac can protect the eggs from parasitic wasps, or from predation - sometimes from other spiders. In addition, egg sacs are often guarded by the mother, like the Neriene montana above (28/05/2014) or Garden spiders (below), Araneus diadematus, which guard their large egg sacs until they die at the end of autumn (30/10/2011).
Holding the egg sac is another maternal behaviour. An example is Pholcus phalangioides, the splindly daddy long-leg spider. She makes a simple egg sac, with the eggs clearly visible through the lax packaging. She keeps the eggs on her mouthparts until the spiderlings hatch (22/07/2009).
Being mobile spiders, wolf spiders and nursery web spiders actually carry their egg sac with them wherever they go. This allows the eggs to develop faster, as they warm up when spiders bask in the sun.
Wolf spider, Pardosa sp. carrying her egg sac (31/05/2011), attached to her abdomen.
Nursery web spider carrying its large egg sac (19/06/2011).

In the family Gnaphosidae, the female not only guards the eggs, but she makes her egg sac inside a folded up leaf, locking herself inside with the eggs (19/07/2010):
But egg sacs are often found alone. Some of them have a stalk, like those of the genus Ero, also distinctive by their covering of coarse red silk (7/04/2013):
Others are truly unique, and is the best way to identify the species, like the sputnik-like egg sac of Paidiscura pallens, a tiny spider (28/05/2014).
Eggs vary in colour, I love the soft pink eggs of Steatoda bipunctata (28/05/2014)...
 ...and also the baby blue silk of Enoplognatha sp., revealed here while picking apples (30/08/2011):
These are just a few examples, from common spiders you can find in your own garden, which illustrate some of the diversity of spiders.

Wednesday, 4 June 2014

New guest in the bee hotel

As I removed one of the sides of the bee hotel to examine the progress of the Red Mason Bee nests I found that one of the cells had been occupied by a mature Mouse Spider female, Scotophaeus blackwalli, in her silk cell, looking like she will be ready to nest soon. Although she retreated to the bottom of the groove, she was still there the following day.
These spiders wrap their eggs in round white silk sacs under bark or in crevices in and around houses, and the female sits by the nest, guarding it. These spider nests are not easy to observe without disturbance, as they may fall apart as they are uncovered, or the female might flee. I am therefore quite pleased with this new guest, as, if she decides to stay, I should be able to watch her nest with little disturbance.

More information on the family Gnaphosidae here.

Brown scale insect

A garden ant stimulated this scale insect to produce honeydew with her antenae. Some these scale insects, Parthenolecanium corni, are growing on a grapevine branch, just under strips of bark. They are about 5 mm, dark and shiny, with ridges across. When young, they are tiny and mobile and are called crawlers, and live under leaves. When they are ready to moult into the immobile scale stage they move into branches. Scale insects, as aphids, suck the sap of plants, and excrete a sugar rich liquid call honeydew, which ants like.

 These scale insects can become a pest of various fruit trees. The scale insect has natural enemies, though. Parasitoid wasps inject their eggs into the scale insect, and the larvae will emerge though holes in the scale, instead of the crawlers. A parasitised scale insect after the wasps emergence is shown below.