Pisauridae: Nursery web spiders

This is one of my favourite spider families, which displays a treasure trove of fascinating natural history. The family has just three medium size or large species in the UK, a terrestrial wandering hunter, Pisaura mirabilis, commonly known as the nursery web spider, and two semiaquatic species, the fishing spiders or raft spiders of the genus Dolomedes, able to run on water and dive to escape danger. I am yet to see a Dolomedes, but you can watch a video of the raft spider Dolomedes fimbriatus, a rare, protected species in the UK, with footage of courtship, egg sac building and maternal behaviour. Adult nursery web spiders do not make webs for hunting, but they build nursery webs for their young. The young (and some non UK species) do hunt with webs. These spiders have long, stout legs and they often hold the first and second pairs of legs extended together, like in the photo below.
Nursery web spiders are easy to recognise, they often have a pale line on their cephalothorax and parallel lines along the body. They are quite variable in the tone and colour of the lines, as you can gather from the individuals shown here.

Pisaura mirabilis basking in typical posture

Food for sex and feigning death

The reproductive behaviour of Pisaura mirabilis has attracted the attention of many researchers. When adult, males will catch an insect, wrap it in silk and search for females. It is thought this behaviour is elicited by the male coming across female silk drag lines, possibly impregnated with pheromones. When they find a female they present her the gift in their chelicerae while raising his body and front legs and palps (watch this video of the approach). If the female accepts the gift they will mate. Males without a gift have reduced chances of mating with females, but sometimes males 'deceive' females by wrapping some insect carcass or a piece of debris to offer the female. Presenting a silk wrapped gift increases the chances that mating will be completed before the females grab the parcel and run away. If the female shows aggression, the male can immediately become immobile (death feigning), while still holding his present. When the female renews her interest in the parcel the male comes back to life and resume mating.  

Male Pisaura mirabilis in another typical resting position. Note its swollen palps.

This male has captured a greenbottle fly.

Maternal behaviour
During the summer, in the lower level of meadows and other open, sheltered places, amongst grass and wildflowers, you might be lucky to come across a female Pisaura mirabilis carrying her large, white egg sac. She holds the egg sac on her chelicerae and palps until the spiderlings are ready to hatch, and despite her long legs, she looks like is walking on tiptoes with her cumbersome load. Once the young start to hatch, she loosens the egg sac and attaches it to a blade of grass. She then builds her nursery tent around the egg sac, where the spiderlings will reside for a while.

Female Pisaura mirabilis with fresh egg sac. Compare with the texture of the older egg sac on the top shot, note that the female on the top shot has a piece of egg sac covering between her chelicerae, so she might well have already loosen up the covering of the sac in preparation for building her nursery.

Nursery web with spiderlings. The spiderlings will form balls like in Araneus diadematus, and the balls also 'explode', with the spiderlings running away from each other when disturbed.

A female standing guard by her nursery web. The spiderlings will disperse after their second moult. Later in the summer, she may lay another batch of eggs.

Wildlife garden meadow unfurling

The meadow in the wildlife garden is growing fast, speckled with buttercups and with the wide geranium and cranesbills carpeting it. Today it was warmer than previous days, with sunny spells. In the morning, I checked for insects and spiders. Female wolf spiders, at least two species, basked with their egg sacs. I also spot several nursery web spiders, I try to get close without spooking them, slowly crouching down to their eye level. When they bask, they often cross their front legs in front of them (above), but if they sense danger, they spread them out or just dash down into the grass. I see several males, each of them with a distinctive colour pattern.

Rhopalus subrufus

The large narcissus fly, Merodon equestris, many around, my first of the year.

A Scatophaga sp. fly

A Lucilia sp. greenbottle

Mating 14 spot ladybirds.

An unfortunate 7-spot ladybird fell prey of the teasel.

Wolf spider with egg sac.

Amber snail, many on the rotting vegetation around the ponds edge.

Cheilosia sp. a hoverfly on a buttercup.

Mating Corizus hyoscyami

A very pale grey male.

The same male than the top shot.

No butterflies, today, just a few Mint moths, Pyrausta aurata, in the marjoram.

Sunbathing Nursery web spider

A sunny day, we visit the wildlife garden. We find little in the way of invertebrates, but, as we are about to leave, on the south facing Ivy, I spy this young Nursery Web spider, Pisaura mirabilis, which makes my day. First she is sitting like some wolf spiders or crab spiders, sometimes sunbathe, with their front legs curled up, looking very relaxed. Then she seems to detect my presence, and it stretches out her front legs in the more typical position of the species (above).

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.

Colourful nursery web spiders

The population of Nursery Web Spiders is thriving in the meadow of my local wildlife garden. I counted no less than 11 today, sunbathing in the long sunny spells between showers. They are striking, easy to spot spiders, that like to stretch to sunbathe like wolf spiders, but keeping their front pair of legs stretched forward together. Many were visible close to each other in various leaves of the lush vegetation, which made apparent how variable in colour they are, from ashy grey to brown and orangey or reddish. They all have longitudinal stripes, with the darker stripes on the cephalothorax. They will probably be mature or mature soon, so males would be capturing flies, wrapping them in silk and offering them to females, while they play dead in order to survive the encounter and make copulation more likely.

Male

Female

More information
British Arachnological Society page.

Summery wildlife garden

A walk around the lush meadows of the wildlife garden yielded a number of invertebrate sightings. The day flying Six Spot Burnet moths, with their bright red-pink and dark metallic wings feasted on the knapweed (above).

A Meadow Brown feeds on the abundant oregano.

I caught a Small Skipper and a Six spot burnet on knapweed.

These are two shots of Small Skippers, one of my favourite butterflies. The way they carry their wings, held at different angles, instead of pressed together like other butterflies, is quite characteristic.

On the grass, there were many nursery webs of the nursery web spider Pisaura mirabilis. With a bit of patience, the guarding females could be spotted on or under the tents. She guards the eggs, and then the spiderlings which hatch inside the nursery web and remain in it for a few days.

A female Pisaura mirabilis.

My first summer generation Comma Butterfly.

And the first Gatekeepers. These two weren't wasting any time and were mating

Male Gatekeeper.

A Ringlet sat atop a ragwort inflorescence. Once I got closer, I realised the butterfly was dead, prey for a spider that often builds its web under flowers, Enophlognatha ovata.

This large hoverfly is one of my favourites, Chrysotoxum festivum. I often see a male hovering over the pond in the wildlife garden.

I took this shot on the 9th of July this year of the hovering male.

And in the oregano, a cuckoo bumblebee, Bombus ruderarius rupestris which parasitizes the similar looking Bombus lapidarius.

The sunny side of the fence

The outside of our garden fence is east facing. Many insects and spiders like to bask on it: even normally ground loving invertebrates climb up on it to get the sun a bit earlier. In the last few days I have been watching (mainly) spiders on the fence early in the morning. The male Nursery Web spider (Pisaura mirabilis) on the top shot, warms up on the side of the fence, in almost the same spot every day.

After warming up yesterday he went down to the weeds at the base of the fence to hunt, and caught a greenbottle fly

A crane fly resting, legs outstretched on the fence.

A male Xysticus cristatus, much darker in tone than the female. This is a ground dwelling crab spider and he was basking about 10 cm from the ground, but it is much easier to spot on the fence.

And an eager male Wolf Spider displaying to the female. Alternatively lifting each palp, trembling and getting closer to her very slowly on tiptoes. She kept tapping the ground with their front legs, and didn't miss a movement. When he got very close, almost touching her, she retreated cautiously, tapping regularly.