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This is where I post various musings about wildlife and ecology, observations of interesting species (often invertebrates)
and bits of research that grab my attention. As well as blogging, I undertake professional ecological & wildlife surveys
covering invertebrates, plants, birds, reptiles, amphibians and some mammals, plus habitat assessment and management
advice
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Thursday, 4 February 2016

Headlights and zebra stripes



Zebra spiders in the genus Salticus are a familiar sight in and around houses and other buildings in Britain and other parts of northern Europe, and their common name derives from their striped pattern.

Salticus scenicus, a common species near buildings.
As for other spiders in the family Salticidae ('jumping spiders'), the carapace ('head') is more-or-less squared off at the front with two large central eyes facing forward and two smaller ones at the corners (red lines in the image below). These are highly mobile with highly developed focusing mechanisms, and are able to see both colour and polarised light.  Just behind these are two tiny side-facing eyes (green lines) and then two more small, but easier to see ones (blue lines); these smaller eyes mainly detect movement and the spider is likely to turn quickly towards a moving object to focus to larger eyes on it.

Eyes of S. scenicus
This arrangement gives good forward binocular vision, unsurprising as they hunt by leaping at prey rather than by using a web. Instead, they attach an anchor-line of silk to the surface it is on, then the rear two pairs of legs are drawn in before being rapidly extended by pumping body fluid into them. In side view, the importance of frontal vision is clear as the carapace is extended forwards to form a short rostrum protruding above the legs.

On the hunt: S. scenicus emerging from a hole in a 'bug hotel'. The large front-facing eyes can be clearly seen.
Although S. scenicus is the commonest species to be found near buildings, there are other species in this genus and it is worth checking for them. They can be separated looking at the epigyne (in females) or the palps (in males). The clear presence of a large palp used in reproduction shows this is a male and its shape (circled below) is typical of S. scenicus.

Male S. scenicus showing the shape of the palp.
Though fairly small (this one is 5-6mm long, excluding legs), 'jumping spiders' are highly active in warm conditions, and therefore often seen - they are worth looking out for and even if you are not a spider-fan, they can be highly charismatic little creatures.

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