Sunday, 15 November 2015

Wandering male lace weavers

In the last week I have found two different males Amaurobius similis wandering, one in the porch and the other in the house. Note the different abdominal pattern in the photos below, especially the dark blotches surrounding the cardiac mark (the midline elongated area over the abdomen). In this species, mature males are most likely to be found between September and November, and they abandon their webs in search of the female retreats. I released them both after taking their photo paying especial attention to the palp (above), which is diagnostic and separates this species from the similar one A. fenestralis. Males A. similis have an inward pointing, curved sharp projection on its palp, which in A. fenestralis is thicker and blunt.
Male 10/11/15.
Male 15/11/15.

Tuesday, 3 November 2015

Spiders in glasshouses

Today at work, I had the chance of inspecting some glasshouses in the Thwaite Botanical Gardens of the University of Hull. They are heated glasshouses holding cacti, succulents, ferns and other plants from around the world. I was pleasingly surprised by the diversity of spiders in them. I found a single Woodlouse Spider, Dysdera crocata, under a bin (above). Quite fitting as we were collecting woodlouse for a practical on woodlouse diversity. The students were quite impressed!
 The first surprise was to find several Walnut Orb Weavers, Nuctenea umbratica. We dislodged an individual from a tree growing in a pot and it proceeded to play dead, legs drawn in, as they do when disturbed. They are usually nocturnal, spending the day in a crack in bark, but this large female I found later was sitting in the middle of her web, I wonder if the reason is it was a very dark, overcast day. There were many more smaller sized individuals, also sitting out in their webs, and it is quite likely this spider matures on her second year of age.
Mature female Nuctenea umbratica.
A student pointed this female Tegenaria to me, she found under a tarpaulin.
A mature, gravid Araneus diadematus sitting on her web.
This was the second nice surprise. One of the glasshouses held a healthy population of Garden Centre spiders, Uloborus plumipes.
By the toilets, a number of Pholcus phalangioides.
Where there are windows, there are window-frame spiders, Zygiella x-notata
I found a single Ero sp. egg sac. These spiders abandon their characteristic egg sacs, and they are not the easiest to find.
On a window ledged, a female Araneus diadematus looking like it has seen better days. Its abdomen shrivelled. Her days are counted after she lays her eggs and weaves her egg sac.

Thursday, 29 October 2015

Liocranidae: spiny-legged sac spiders

Credit Gerhard Elsner CC BY 3.0 via Wikimedia Commons.

A small family with 13 British species that used to be regarded as part of Clubionidae. All species are mainly nocturnal wandering hunters, except the two species of the genus Phrurolithus, which are diurnal ant mimics, and have been also regarded as a different family.

Distinctive egg sacs
Agroeca have distinctive stalked egg sacs, like inverted wine glasses (top shot), sometimes covered with soil, which are seen more often than the spider, as they are not guarded. Other species guard their egg sacs.

Spiders have many species of external and internal parasitoids, most of them ichneumonid wasps. Some external parasitoids attach themselves to adult spiders and feed on them, other species search for cocoons and inject their eggs on egg sacs, with the parasitoid larvae developing on the eggs. The characteristic egg sacs of Agroeca makes them easy to identify and collect, so in a study of spider adult and egg sac parasitism in Germany, up to 66% of Agroeca egg sacs were parasitised. Four species of parasitic wasps emerged from egg sacs: two small Gelis wasp species, Bathythrix formosa, and Thaumatogelis audax. Few or no spiderlings emerged from the parasitised egg sacs, indicating how important parasitoids can be as a source of spider mortality.

More information
Finch, O. D. (2005). The parasitoid complex and parasitoid‐induced mortality of spiders (Araneae) in a Central European woodland. Journal of Natural History, 39: 2339-2354.

Wednesday, 28 October 2015

Anyphaenidae: buzzing spiders

Credit gbohne, CC BY-SA 2.0, via Flickr.

A mainly American family with a single UK species, Anyphaena accentuata, that can be recognised by arrow head markings on the abdomen. They are good climbers that live on the foliage of trees in woodland and scrub, where they hunt and mate. They are active hunters that pounce on insects that sit on leaves such as leafhoppers, aphids and flies.

Buzzing spider
Males of this species (top shot) use acoustic cues in courtship, vibrating the abdomen and tapping with the palps while sitting on a leaf. This produces an audible noise (which may be undetectable for older people), so Bristowe suggested the name buzzing spider for them. This is a short clip of this behaviour. Females may respond to these signals by approaching the calling male. Females attach their egg sac to the underside of leaves and guards it in a thin silk cell.

Cold adapted
Immature buzzing spiders are active year round and have physiological adaptations to activity during cold temperatures, even below the freezing point. In the winter they prey on small insects that live on bark.

Tuesday, 27 October 2015

Dictynidae: mesh weavers

Credit: Drriss & Marrionn CC BY-NC-SA 2.0 via Flickr.
These are small cribellate spiders, less than 5 mm long, some with characteristic colour patterns. They build an irregular sheet web usually with a central retreat. Many of the 18 British species are uncommon. Some of the species live on plant foliage, others are ground dwellers.
 The top shot shows Nigma walckenaeri a green and white spider that builds sheet webs on the top surface of leaves. This species is mainly found in the Thames and Severn valleys, where it can be common in gardens.

'Unusual friendship' between males and females
 Dyctina arundinacea, the most common species, makes its web atop a dead shoot or flower head. The spider adds more threads as the summer progresses, for, unlike orb weavers, the web is a permanent structure. Bristowe remarked that in this species, the male spends an unusually long time in company of the female in her web (a month or more). Once a male enters a receptive female's web, he signals to her and she signals back with vibrations and tactile signals. The male then goes on to modify the female's web and adding threads to build a canopy, where mating happens. They signal to each other every time they meet. Males and females can even share capture and eating of prey. The female sets her egg sacs inside the web, and she can produce up to six in a season. While a male have to gain from staying around a female, for example, preventing rival males from mating with 'his' female, it is unclear what the female has to gain from accepting the male, unless his cooperation in prey capture helps she build up resources for egg production. More research is needed on these spiders natural history. There are tantalising observations of  males possibly participate in egg guarding. Some non European Dictynidae are social, so it is possible that the roots of social behaviour lay on these unusual male-female associations.