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.

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