The Way I See Things


Knobbly knees

I got myself tied up with preparations for some upcoming festivities this morning, and by the time I tore myself away from the computer and stomped down the garden with the camera, the nice light of 9am had given way to deep gloom - not least mine, because it was also cold, and invertebrate pickings were very thin indeed.

Best of the day was this female Dicranopalpus harvestman - unidentifiable reliably to species without a microscope, as I pointed out in this post, but most probably Dicranopalpus ramosus, which is thought to be more common than the very similar Dicranopalpus caudatus. D. ramosus is also said to be the larger and more robust of the two, and this specimen was a healthy 5-6mm, but obviously size comparisons aren't especially helpful when you're faced with a single individual.

This pose, with the legs fanned out to the sides, is characteristic of the species; the longest of the legs, especially the second pair, can reach 5cm. It's worth noting that this old lady has had a slightly hard life, and is missing two of her legs on the right side. When attacked, Opiliones can self-amputate a limb - a process called autotomy - in order to confuse the predator and give themselves time to escape, but the missing limb will not regrow, which obviously has a cost in terms of the individual's future speed and strength.

I know that this is a female because of her lumpy abdomen, rising to a bump at the distal end, and the dark girdle around her 'waist'. Males are smaller, flatter, and generally darker, and they sometimes have a dark stripe across the eyes, like a highwayman's mask. I posted a male to my Facebook page recently, if you'd like to compare them.

As to the knobbly knees: her pedipalps, which look as though they're forked, and give her the rather dangerous appearance of having claws or pincers, aren't really forked at all. The apparent branch is actually an outgrowth of the palpal patella - or in other words, a knobble on her knees.

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