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).
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.
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.