Introduction

The spider fauna of East Africa is not particularly well known, but one group of spiders, the sheetweb weavers or dwarf spiders (family Linyphiidae), is much better known than any other group. This is quite strange since these spiders are small (most spiders are less than 3 mm in total length) and do not have any remarkable body colours. The family Linyphiidae is one of the largest spider families (second only to the jumping spiders, Salticidae) with some 3600 species described in 403 genera (Platnick, 1989).

The common English names for these spiders (dwarf or sheet-web spiders) are not very appropriate, since linyphiids are not smaller than spiders in several other families and sheet webs resembling those of linyphiids are also built by members of other spider families such as the Theridiidae, Cyatholipidae, Diguetidae, Pholcidae, Araneidae and Uloboridae (Eberhard, 1990). Furthermore, sheet webs are built only by some linyphiids, particularly representatives of the subfamily Linyphiinae.

An impressive amount of information on the East African linyphiid fauna has been published during the last 30 years, especially on the montane fauna. In East Africa, many mountains have now been explored at least once and this has revealed a relatively rich linyphiid fauna. However, ‘rich’ should be understood in an African context, as the diversity is low if one compares the number of species on each mountain in East Africa with the number of species on mountains in the northern hemisphere.