Saturday, February 2, 2013

Stalkers: Jumping spiders

Jumping spiders are active hunters often seen during the day walking up and down walls in houses as well as in the countryside. They hunt flies and mosquitoes by stalking them slowly and finally jumping on them. 

At least two species are found in the Maltese islands although one should not be surprised if more are discovered as spiders have not been studied completely in the Malta.

The most common species is known simply as the jumping spider but is also called Adanson's House Jumper. In Maltese it is known as brimba qabbeżija tad-djar. It is found in warmer climates around the world, including Japan, Taiwan and Australia but has been introduced in many parts o the world including colder areas where it is often found in greenhouses. A male jumping spider can grow up to 8 mm.

Another species known as Schembri’s jumping spider, brimba qabbeżija ta’ Schembri, is much smaller growing to a maximum of 4mm. It is found on dry ground among stones and is endemic to Malta and Sicily.

The jumping spider family contains over 5,000 species, making it the largest family of spiders with about 13% of all species. They are found in a variety of habitats especially in tropical rain forests but they can also be found in temperate forests, scrubland and on mountains. 

One specimen is claimed to have been collected near the very top of Mount Everest. Jumping spiders have good vision, which they need for hunting. They have four pairs of eyes, some of which are sensitive to a wide range of rays including ultraviolet rays.

Jumping spiders have a well developed system of internal hydraulic which makes it possible for them to extend their limbs by changing the pressure of their blood within them. Thanks to this system they can make spectacular jumps without the need of having large muscular legs like the grasshopper. 

A jumping spider can jump 20 to 60 or even 75 to 89 times the length of its body. When a jumping spider is moving from place to place, and especially just before it jumps, it tethers a filament of silk to whatever it is standing on. Should it fall for one reason or another, it climbs back up the silk tether.

Jumping spiders are very curious creatures. When approached instead of moving away they turn to face the possible danger. If approached too closely they might jump backwards and they might also attempt to defend themselves by raising their forelimbs.

Reproduction involves an interesting courtship display consisting of complex movements of the forelimbs in which the male’s hairs and colours are shown off to the female. It is thought that in at least one species the female reflects ultraviolet rays before mating. It has also been recently discovered that many jumping spiders have a good auditory system and that males make sounds like buzzes and drum rolls. 

This article was published in The Times on 10 June 2009.

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