Menemerus bifurcus

Menemerus bifurcus is a species of jumping spider in the genus Menemerus that lives in South Africa, Zambia and Zimbabwe. The species was first described in 1999 by Wanda Wesołowska, one of over 500 descriptions she has written during her lifetime. The spider lives in groups in Acacia, Combretum, Jacaranda, Spathodea and Trichilia trees as well as in houses and other areas of human habitation. It descends to attack prey on long threads of silk. It is a small spider, with a carapace that is between 1.9 and 2.3 mm long and an abdomen between 1.9 and 2.5 mm long. The female is larger than the male and generally lighter, ranging generally from fawnish-brown to dark brown. The species is similar to Menemerus formosus and Menemerus transvaalicus but differs in the design of its copulatory organs. The male has a short embolus with a longer lamella, which is recalled in the species name, and two distinctive tibial appendages, or apophyses, one with a characteristic triangular lobe. Examples found in Zimbabwe have one longer tibial apophysis. The female has a heart-shaped depression in the epigyne and an unusual insemination duct morphology.

Taxonomy
Menemerus bifurcus is a species of jumping spider that was first described by Wanda Wesołowska in 1999. It was one of over 500 species identified by the Polish arachnologist during her career, making her one of the most prolific in the field. She allocated the spider to the genus Menemerus. The genus was first described in 1868 by Eugène Simon and contains over 60 species. The genus name derives from two Greek words, meaning certainly and diurnal. The genus shares some characteristics with the genera Hypaeus and Pellenes.

Genetic analysis has shown that the genus is related to the genera Helvetia and Phintella. The genus was placed in the tribe Heliophaninae until that was reconstituted as Chrysillini by Wayne Maddison in 2015. The tribe is ubiquitous across most of the continents of the world. It is allocated to the subclade Saltafresia in the clade Salticoida. In 2016, Prószyński created a group of genera named Menemerines after the genus. The vast majority of the species in Menemerines are members of the genus Menemerus, with additional examples from Kima and Leptorchestes. The species name derives from two Latin words, bis and furca, which describe the shape of the male's embolus.

Description
Menemerus bifurcus is a small spider. The male has a flat dark brown carapace that is between 1.9 and 2.1 mm long and between 1.3 and 1.6 mm wide, covered in short brown and whitish hairs. Lines formed of white hairs line the sides of the carapace. It has a darker eye field. The spider has a very low brown clypeus that has white hairs. The chelicerae and labium are light brown; the maxilae and sternum are orange. The abdomen is between 1.9 and 2.0 mm long and typically 1.6 mm wide. Most examples have a fawnish-brown abdomen, while some are dark brown. Some have a light pattern of three or four spots, although this is usually quite faint. The underside is light. It has brownish spinnerets and brown or orange legs. The pedipalps are brown with white hairs visible on the palpal femur. The embolus is short with a lamella that is of a slightly longer length. The cymbium has a large lump at its base. The palpal bulb has a distinctive arrangement of two tibial appendages, or apophyses. One is short and stumpy, pointing upwards, and the other is longer and points downwards.

The female is larger than the male. It has a carapace that is between 2.1 and 2.3 mm long and between 1.6 and 1.8 mm wide and an abdomen between 2.1 and 2.5 mm in length and between 1.7 and 1.8 mm in width. It is generally lighter. The carapace is fawnish-brown covered with brown hairs. The eye field is dark brown with white hairs. Dark rings encircle the eyes. The chelicerae, labium and maxillae are orange. The sternum is yellow. In some examples, the abdomen is yellowish all over with a covering of brown hairs; in others, it is similar to the male except lighter. The spinnerets are always yellowish. The epigyne has a wide notch on the rearmost edge and a heart-shaped depression. The copulatory openings lead to wide highly sclerotized insemination ducts that have an unusual morphology. There are distinctive accessory glands and small spermathecae.

Spiders of the Menemerus genus are difficult to distinguish. The species is particularly similar to the related Menemerus formosus and Menemerus transvaalicus. Externally, they are hard to distinguish but the copulatory organs are very different. For example, the male has a distinctive triangular retrolateral lobe below an unusual dorsal apophysis which the others lack. The female has more sclerotization throughout its copulatory openings. The shape of the epigyne depression is also distinctive. There are also differences between examples found different areas. The male spiders found in Zimbabwe have a longer tibial apophysis than those from Zambia.

Behaviour
Menemerus bifurcus does not spin webs. Instead, it lives in the tops of trees and descends to attack prey on long threads of silk. The spider makes a dense cocoon when moulting. They live in groups in loose association with each other. They have been noted to mate between September and January. Juveniles appear in both March and April. Menemerus spiders undertake complex displays and dances during courtship. The males also undertake aggressive displays between themselves. They are hesitant attacking other spiders. The species nests under strips of bark and between flat overlapping flakes of bark. Generally, the spiders are difficult to observe in the wild, being secretive and shy, and using camouflage well.

Distribution and habitat
Menemerus spiders are found throughout Africa and Asia, and have been identified as far as Latin America. Menemerus bifurcus is found in South Africa, Zambia and Zimbabwe. The male holotype was found near Kitwe, Zambia, in 1963. Zimbabwean examples have been seen in Bulawayo in 1962 and Harare in 1998. Examples found in South Africa are found in Rust De Winter Nature Reserve in 1972, Pretoria in 1976 and Tshipise in 1979. The spider lives in trees, particularly the bark of Acacia, Jacaranda and Spathodea trees. Examples that live in the Sengwa Wildlife Research Area in Zimbabwe have been found on the bark of trees of the Combretum genus and trunks of Trichilia trees. The spider also lives in houses and areas of habitation, including the museum in Bulawayo.