Subject: Spider ID
Geographic location of the bug: Llubovane Dam, Eswatini, Southern Africa
Time: 12:03 AM EDT
Your letter to the bugman: Good day,
Please can you ID these two spiders. The large one is beautiful. They were on a dead tree stump in the dam. The large one was walking down the stump under the water and coming back up, perhaps looking for food?
How you want your letter signed: Jacqui
The behavior you witnessed, “large one was walking down the stump under the water and coming back up, perhaps looking for food?”, and the markings on the carapace are both consistent with Fishing Spiders from the genus Dolomedes found in North America, as evidenced by this BugGuide image. While we have not had any luck locating any similar looking South African members of the genus, according to Wikipedia: “The second largest number of species occur in tropical Africa.” Perhaps one of our readers will be able to identify your gorgeous spider to the species level. We do not know the identity of the smaller Spider in your image. According to Science Direct: “Sierwald (1988) examined predatory behavior of the African pisaurid Nilus curtus O.P.-Cambridge (=Thalassius spinosissimus [Karsch]). Its hunting posture is like that of Dolomedes, anchored by one or more hindlegs to an emergent object with its remaining legs spread on surface of water. When disturbed, the spider pulls itself below the surface of the water by crawling down an emergent object. They can remain submerged for up to 35 min. Prey swimming under water (insects, tadpoles) are grabbed by the front legs pushing down through the surface film. Prey trapped by surface tension were jumped on if close enough, or rowed to if further away.” Members from the genus Nilus pictured on iNaturalist do resemble your individual.