07 June 2009

Jumping Spider - Opisthoncus machaerodus

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Jumping Spider - Opisthoncus machaerodus

Jumping Spiders belong to the large Salticidae family, where amazingly there are 76 genera with over 250 species in Australia alone. Opisthoncus is one of the larger genera with 25 described Australian species, but there are many more Jumping Spiders worldwide generally in tropical regions. These spiders are small, usually around 1 cm 3/8" or less, but more than make up for their lack of size by being if not the most cute looking, then certainly the most intelligent of spiders. These spiders do not build webs and are sophisticated and active hunters, often capturing prey several times their size. They have two very large eyes on the front of their face, another two smaller ones around the sides and four on top, giving them excellent vision in most directions and an ability to interact with human observers.

There have been many studies done on these engaging spiders and commonly their hunting tactics are noted as being unique amongst the spider fraternity by being cat-like. Apparently they will sneak up on their prey, rarely approaching it directly, but by visually assessing the best and most secretive route, will circle, keep out of sight and even go in the opposite direction in order to deceive and to reach the most favourable position to leap onto the prey and speedily immobilise it with a bite.

Opisthoncus machaerodus is the only Opisthoncus species known for the Esperance region, so once the genus had been ascertained (with the assistance of Dr Ron Aitkinson, University of Southern Queensland, whom I am extremely grateful), the species name was easily found. Interestingly, with this group of spiders the male is often a very different color to that of the female and in this instance is the small black spider, which was no more than 8 mm (slightly more than 1/4"), whilst the pale brown female was a little larger at 10 mm or 3/8" in length.

Usually Jumping Spiders are seen during the day when then can put their excellent vision to good use, but with this species I have only encountered it at night, which may only mean that this spider will sometimes also hunt at night. On all occasions they were encountered on Grasstree (Xanthorrhoea) fronds, possibly because they are easier for me to see them in this environment, plus it may be easier for the spiders to see insects at night in this environment.

In Australia, Queensland and NSW have by far the greatest number of Jumping Spiders and I can only envy their naturalists the opportunity to discover these very engaging little spiders.