Thursday, September 26, 2013

Lovely Legs

Today's Guardian Country Diary is about encounters with harvestmen while clearing an overgrown garden.

Although they're often referred to as harvestmen 'spiders' they belong to a quite different taxonomic order from true spiders and have none of their menace, mainly because they lack large poisonous fangs but also because of the tentative, non-threatening, painstaking way that they move. Those long legs are not just for walking - the second pair also carry their senses of touch and smell, which are far more sensitive than their single pair of tiny eyes that are mounted on a turret on their topside. 

When you watch a harvestman on the move it gently feels its way over new territory by extending that extra-long second pair of legs, constantly touching the ground ahead and picking up scents. If you put two harvestmen together in a confined space they'll each extend their second pair of legs towards each other, picking up each others' scent.

Harvestmen scavenge dead animals and will eat fungi and drink juice of ripe fruit, but they are also hunters, catching and eating animals smaller than themselves. There is one intriguing account of a harvestman penning up its prey within a circle of those long legs, drawn close-in to its body, then dropping on its prey like a pile-driver. 

A variety of animals prey on harvestmen, including frogs, toads and birds. On a couple of occasions I've seen robins with their beaks full of harvestmen in autumn. 

They have two forms of defence. One is the secretion of a noxious fluid, said to smell of walnuts, which will deter small predators like ants. Their last line of defence is autotomy - the shedding of legs to allow then to escape a predator's grip (or the sticky threads of  spider's web). It's common to see harvestmen with fewer than the full complement of legs at this time of year but if they lose the second pair - and with them their vital senses of smell and touch - they stop feeding, essentially losing the will to live.

This is the pose adopted when they're faced with a threat, with that second pair of legs extended as wide apart as possible - assessing the threat by detecting its scent.

Although they tend to move slowly and precisely they can, if the need arises, run with considerable speed over uneven surfaces - like long grass, for example - thanks to those amazingly long legs that allow them to simply step over objects that would slow shorter-legged animals down.

At this time of year harvestmen will be laying eggs, which will overwinter and then hatch  next spring as nymphs, which will then slowly grow larger as the summer progresses.


No comments:

Post a Comment