11 July 2013

Spotlight on the species Salticus scenicus

Hello dear reader and welcome to another Spotlight post!  This time we place our spotlight squarely on the "Zebra Jumping Spider," Salticus scenicus.

This tiny jumping spider is only 5-7mm long and commonly found across in North America and parts of Europe. Characterized by its bold black and white stripped abdomen, this tiny spider portrays a comic personality to many observers thanks to its curiosity and tendency to look up at its viewers.

A female Salticus scenicus intently focused on a nearby object.

Unlike many salticids, this species is very commonly found in urban areas, especially on the sides of buildings and window screens.  They are also unusually tolerant of other salticids.  Most salticids stay as far away from each other as possible unless they are looking for mates.  S. scenicus, however, seems to thrive in very dense populations and can often be found within only a few centimeters of each other.  Out here in the Midwestern USA, I frequently find this species in groups of 4 or more within only 2-3 square meters.  While this may not seem that impressive, members of the genus Phidippus (our previous spotlight animals) are rarely found in densities greater than one or two per building face, much less several on the same side of the building. 

 Another interesting aspect to this species is the cheliceral sexual dimorphism.  Whoa, ok wait, lets back that up.  For our newer readers, chelicerae are the spider's mouth parts that most people incorrectly call the fangs.  I say incorrectly because on most spiders, the fangs are tiny and tucked into the chelicerae.  I've added a grey arrow to the picture below to indicate the chelicerae, and a green arrow in the following photo to indicate the fangs.


A Male Salticus scenicus showing off his extra large chelicerae, indicated by the grey arrow.

The same male S. scenicus with his fangs (green arrow) unfolded from his chelicera.

 The second thing I should explain is sexual dimorphism.  All that fancy term means is that the males and females of a species look different from each other.  Sometimes this difference is very drastic, as is the case in many birds.  Other times, the difference is much more subtle, like in S. scenicus. The most obvious difference between the males and females of this species are the greatly enlarged chelicerae and fangs of the males, as is shown above. Obviously, S. scenicus is the exception to the rule of tiny fangs, but for a good reason!  The males of this species use their enlarged mouthparts in male-male combat when they are sparring over access to females during the breeding season. In spite of these over-sized fangs and chelicerae, the species as a whole is quite timid and will usually run and hid if you attempt to do anything other than look at them.

There is a lot we can learn from this tiny species, especially given how readily they've adapted to cohabitation with people. The next time you're outside and its a nice warm day, take a look around and maybe you'll be graced by the presence of one of these tiny little hunters.  Who knows, it may even be clearing out your local mosquito population for you too!