If I were…

If I were an opiliophile in Iceland… I would only encounter four species1. And of these four, only Mitopus morio is widely spread over the island, living at the seashore, in the mountains and on the many islands and islets. The other three species, Nemastoma bimaculatum, Oligolophus tridens and Megabunus diadema, have only been found in the southernmost part of Iceland. This can probably explained by a combination of their introduction (see last paragraph) and the climate. Winters are relatively mild in the southern part, with temperatures of 0°C on average. In the central highlands, the mean winter temperature is around -10°C and in the north even -25°C. Apparently M. morio can handle such low temperatures!

Figure copied from I. Agnarsson, 1998

Distrubution of Mitopus morio in Iceland. Figure copied from I. Agnarsson, 1998

Despite the narrow distribution range of N. bimaculatum, O. tridens and M. diadema, they can locally be fairly common. N. bimaculatum seems to select south-facing slopes, an indication that the temperature is a limiting factor for this species. M. diadema is most common near the sea, where it lives on moist cliffs. The North Atlantic Current brings warmth to this part of the world, making the climate of Iceland more temperate than would be expected so close to the Arctic circle.

Distribution of Megabunus diadema in Iceland

Distribution of Megabunus diadema in Iceland. Figure copied from I. Agnarsson, 1998.

Most likely, dispersal is the main reason why so few species of harvestmen occur in Iceland, compared to other areas in Europe with a similar climate. In a recent paper, I. Agnarsson explains that M. morio probably is the only species that has reached Iceland without the help of men. It has been present in Iceland for a long time (a report from 1772 mentions that it already was widespread at that time) and it also occurs on locations north of Iceland, including Greenland, where it is the only species of harvestmen. Nevertheless, I think that the possibility cannot be ruled out that this species was hitchhiking with earlier settlers, for example the Celtic monks that came to Iceland in the seventh or eighth century, or Norse settlers that arrived from the ninth century onwards. The recent discovery (1929) and limited but expanding distribution of the other three species points towards their dispersal by men.

1. This post was entirely based on the publication Íslenskar langfætlur og drekar by Ingi Agnarsson (1998). A complete checklist of all Nordic Opiliones was published by Ingvar Stol in the Norwegian Journal of Entomology (2007). Click the links for PDF’s.

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Excursion materials

One of the nice things about harvestmen is that some species can be found year-round. So excursions can be undertaken even in the midst of winter! I have a special bag containing the things I need when I go look for harvestmen. This is the equipment:

Excursion materials

  1. Notebook and pen
  2. Plastic containers
    For examining or taking home specimens
  3. Photo camera
    I take a picture of every specimen I find, so that more experienced people can check the determination before they are entered into the database of the Netherlands. Luckily there are so few species living here that they mostly can be recognized from a picture.
  4. White umbrella
    A light-coloured umbrella is very handy to find specimens that sit in bushes or in the lower parts of trees. Open up the umbrella and place it upside down under the branches, then shake the braches or hit them a few times with a stick so that all invertebrates fall into the umbrella (like this).
  5. Handheld GPS for taking coordinates
  6. Spare batteries for the GPS
  7. 10x magnifier
  8. Determination guide

So, I’m off for today!

Caught on tape

I started to become fascinated by harvestmen after someone asked me to take some photos of these funny little creatures for his collection. Soon after, I decided to buy a guide to help me identify the species and to get some background information. My life as ‘Opiliophile’ could now officially start!

Whether or not you believe in the concept of synchronicity, the next day I had the funniest experience. In the morning before I went to work, I picked up a small plastic tape dispenser from the floor. It fell the night before but I had forgotten to pick it up. And what did I see: a harvestman sat stuck to it! And even better, it was a species that is quite rare in the Netherlands: Odiellus spinosus. Apparently I have some nice species running around on the first floor of my own house, it is only a matter of placing traps! Yes little one, we got you on tape.

I took some pictures and then was able to detach the unlucky fellow from the tape without him loosing any legs. This species is one of the largest harvestmen in our regions, with a broad and flat body that can reach a length of 7 to 9,5 mm. It is well recognizable by the large trident, which has around the same dimensions as the eye hill. The species is actually believed not to be thát rare, but simply not found so often. Probably it is very well capable of hiding itself during daytime, because they can be found quite abundantly in pitfall traps placed in gardens.

Unfortunately I was not able to make good pictures because it was still dark and I had to leave for work. But anyway a few pics to show the situation. If you’d like to see some truly splendid photos of Odiellus spinosus, have a look here.