Male and female behaviour

In some species of harvestmen it is easy to distinguish females and males, while in other species they look more similar. But are there also differences in behaviour? One would expect some, such as that males are more involved in territorial behaviour, or that the females, who have larger bodies and need energy for the production of eggs, spend more time eating. Indeed this is confirmed by some studies.

In studies on both Neotropical harvestman Ilhaia cuspidata and the temperate species Phalangium opilio, the females spend more time feeding while the males were busier with ‘social interactions’: inspecting and attacking other males1/2. In another Neotropical species, Neosadocus maximus, females were resting more, while males spend more time exploring their surroundings, and, perhaps as a result of all that exploring, were busier cleaning themselves3.

Neosadocus maximus is an impressive-looking harvestman by the way, very different from all species that can be found in my regions. It is very large (male body length around 10 mm) and it is even reported to eat small frogs!4 Unfortunately I haven’t seen one myself; the two pictures in this post are made by João P. Burini (see his marvelous photo stream here).

Neosadocus maximus female

Neosadocus maximus female (c) Techuser / João P. Burini

There are indications that males and females also select different locations to rest during the day. In a study where a 100 m long brick wall in the Netherlands was examined on a weekly basis, the males of Opilio canestrinii on average sat higher up the wall than the females5. The author thinks that this distribution develops when males fight with each other for females during the night, thereby trying to get higher up the wall to be in a good position to attack other males from above. In this way, stronger males end up high on the wall and weaker ones on the bottom part. Females would then select the ‘higher’ males for mating, after which they leave the arena to rest on the lower parts of the wall. At dawn the males also go resting, staying at their higher positions.

Neosadocus maximus mating

Neosadocus maximus mating (c) Techuser / João P. Burini

No such micro-spatial pattern could be found however in a study with Phalangium opilioon soy bean plants: both males and females sat mainly on the bottom and middle parts of the plants, with only few visits to the top parts3. At dusk, all P. opilio became active and moved to the ground to forage and mate. Around 4 hours later, larger nymphs and females returned to the plants, while males did not return for another 3 hours, mainly spending the last hours walking.

1. Behavioral Repertory of the Neotropical Harvestman Ilhaia cuspidata (Opiliones, Gonyleptidae). W. Pereira, A. Elpino-Campos, K. Del-Claro and G. MacHado. 2004. Journal of Arachnology, 32 (1):22-30
2. Diel activity patterns and microspatial distribution of the harvestman Phalangium opilio (Opiliones, Phalangiidae) in soybeans. C.M. Allard and K.V. Yeargan. 2005. Journal of Arachnology, 33(3): 745-752.
3. Activity pattern of the Neotropical harvestman Neosadocus maximus (Opiliones, Gonyleptidae): sexual and temporal variations. F. Osses, T.M. Nazareth, G. Machado. Source: Journal of Arachnology, 36(3):518-526. 2008.
4. Harvestmen (Opiliones: Gonyleptidae) predating on treefrogs (Anura: Hylidae)
L.M. Castanho & R. Pinto da Rocha. Link to the article.
5. Hooiwagens op een Nijmeegse muur (Arachnida, Opiliones), II. H. Wijnhoven. Nieuwsbrief Spined 28: 32-35. Link to the article.


River forelands

Last weekend my husband and I set off to the IJssel river forelands to take a walk. And of course I had to look for harvestmen along the way.

IJssel river forelandI especially went looking for Astrobunus laevipes, a small harvestman (2,5 – 4 mm) with two rows of blunt spikes running over its back. It is an originally southern European species, that has been found for the first time in the Netherlands in 20031. It is expected to live along the IJssel, but the area has not been searched often so it has not (yet) been found. We turned over many small rocks, but unfortunately weren’t able to detect one.

IJssel riverThis pile of rocks however was home to a number of Phalangium opilio:

Phalangium opilio male on rockPhalangium opilio male on rockPhalangium opilio male on rockAt the end of the walk we found 3 specimens of Mitopus morio, which made me very happy as I had not seen this species before.

Mitopus morio maleOne male was carrying a parasitic mite larva on its leg:

Mitopus morio with parasitic mite larvaThe female looked a bit faded, perhaps she had to molt one more time:

Mitopus morio femaleMitopus morio femaleSo, al in all, a nice walk, harvestmen-wise and otherwise!

IJssel with wild horse1. H. Wijnhoven (2003) De hooiwagen Astrobunus laevipes nieuw voor Nederland (Opiliones: Phalangiidae). Nederlandse Faunistische Mededelingen 19: 73-78.  Link to article.

Leiobunum blackwalli

Sometimes I see a specimen of Leiobunum blackwalli in my garden. The females of this species have a dark saddle that widens towards the back part of the abdomen and then terminates abruptly: Leiobunum blackwalli femaleLeiobunum blackwalli femaleLeiobunum blackwalli femaleThe males do not have such a pronounced saddle, but are easily distinguished from L. rotundum -which they resemble very much- by the pale ring around each eye where L. rotundum has an entirely dark/black eye hill. (Click to enlarge pictures)

Leiobunum blackwalli maleLeiobunum blackwalli maleL. blackwalli is often found in deciduous forest with dense undergrowth, along forest edges and waterways, in open fields and along the coast. In cities and villages L. blackwalli is much less common than L. rotundum, but not rare either. It is thought that L. blackwalli has decreased in numbers after the invasion of Opilio canestrinii (see last post), but unfortunately its distribution is not monitored well enough to know for sure.

Opilio canestrinii

Opilio canestrinii on treeEven though I have just recently become interested of Opiliones, there is one species I am already a bit tired of: Opilio canestrinii. In itself it is quite a pretty species to look at, but the thing is that you see it literally e-ve-ry-where. One reason is that it is very conspicious: large-bodied and often sitting openly on vertical structures such as trees and walls. The other reason is that it simply is very abundant.

Opilio canestriniiis believed to originate in Italy, but has colonized northwestern Europe with amazing speed over the past decades. In the Netherlands the first specimen was found in 19911 and it already is one of the most abundant species. In all countries where it appears this goes at the cost of other species, that apparently loose the competition and disappear. In the Netherlands as well as in the UK and Germany Opilio parietinus has seriously declined after the establishment of O. canestrinii. The last sighting of this species in the Netherlands was in 2006 and it was believed to be extinct, but in 2012 another one was found. In northern Germany Leiobunum tisciae has also disappeared after O. canestrinii set foot, and L. rotundum and L. blackwalliare probably negatively affected as well, although this has not been proven yet2.

Opilio canestrinii is easily recognizable in the field by it’s large (4-8 mm) orange to greyish-brown body with two rows of lighter-coloured spots on the back and darker-coloured legs:

Opilio canestrinii maleEven though they are similarly coloured, the difference between males and females is quite easy to see in this species. The one on the picture above is a male: it has a relatively small body that is a bit truncated at the back. Due to the body being so small, the trochanters (the light orange ‘bulbs’ between the black legs and the body) seem very prominent:

Opilio canestrinii maleOpilio canestrinii maleThe females on the other hand have much larger bodies with a rounded shape. Especially when they are about to lay eggs the body is very large and swollen.

Opilio canestrinii female

Another female from the front, showing the pedipalps and raised tubercle (eye hill):

Opilio canestrinii female frontThe last one has a more greyish colour, but also is an Opilio canestrinii female:

Opilio canestrinii femaleSee how she’s staring into the camera, inspectingly tapping it with her second pair of legs? More about the sensory legs of harvestmen in a next post!

1. R. van der Weele (1993) Opilio canestrinii nieuw voor de Nederlandse fauna (Opilionida: Phalangiidae), Entomologische Berichten 53: 91
2. H. Wijnhoven (2010) Hooiwagens op een Nijmeegse muur (Arachnida, Opiliones), II. Nieuwsbrief Spined 28: 32-35. Link to the article.

Giant harvestman found in Laos

This month a giant harvestman has been found in a cave in Laos by Dr. Peter Jäger of the Senckenberg institute. They have not yet been able to identify it to the species level, but it probably is a member of the genus Gagrella in the Sclerosomatidae family.

Giant Harvestman Laos

(c) Senckenberg

Giant Harvestman Laos

(c) Senckenberg

While the body of this harvestman is not even 1 cm in length, the legs have a span of 33 cm. That means there is only one harvestman ever found that is larger: a species from Brazil with a span of 34 cm. (Unfortunately I can’t find out which species. Do you know? Please leave me a message!)

The interesting thing is that also other invertebrates reach giant dimensions in those caves in Laos, for example the Laotian huntsman spider Heteropoda maxima (span 30 cm), the whip scorpion Typopeltis magnificus (span 26 cm) and the predatory centipede Thereuopoda longicornis (40 cm). The reason why ‘giantism’ has developed there is still unclear. It is expected however that the invertebrates cannot become much larger than this. Either the oxygen supply would become a problem, or, in the case of harvestmen, the legs would become too long for fast movement.


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.