Category Archives: Arachnida

Op Op…. Opiliones!

As promised, here I am posting some more photos and videos taken in my backyard.

Op Op.... Opiliones!
1.Opilio canestrinii (?, help! 🙂 )

I would like to acknowledge already some information about the opiliones I found on the Web:

  1.  Wikipedia is a nice first reference but I encourage you to check other sources;
  2.  The OmniPaper Project constitutes a GREAT repository of information on Opiliones that you can find under the Aracnolab webpage, from Museu Nacional of Rio de Janeiro [1]. Thank you!;
  3.  A book that I’ve been using to read a bit more – Harvestman: The Biology of Opiliones [2].

At the bottom of this post you can find a few more references. Take it with a grain of salt! I am far from being an expert on this matter. I leave you with some general information that I collected from the aforementioned sources (mostly from the book).

Well, first of all keep in mind that opiliones are not harmful to men at all! They are cute and harmless! Great! The Opiliones order are the third-largest group in the arachnids, after the Acari (mites and ticks) and Araneae (spiders). There are a few thousand of different species of opiliones and four suborders (Laniatores, Eupnoi, Dyspnoi and Cyphophthalmi). Apparently they tend to be more active during the night, I guess it explains why I also saw them mostly the end of the day. I’ve read that there is evidence that some species are inefficient in avoiding water loss. It seems that this can be correlated with being more active during the night. Opiliones’ predators can be found among birds, frogs, toads, insectivore mammals and spiders.

Sensory wise… 🙂 They have a pair of eyes (there are some eyeless species), oriented to the side, but they are unable to form images. Opiliones explore the environment using the tips of their second pair of legs that functions like an antenna. I think you can see this behavior in video 1.

 

Most species are omnivores. Opiliones may eat plants, fungi and small invertebrate. Unlike most arachnids they do not suck their preys’ liquefied tissue. They chew the food by ingestion of small pieces of it. Video 2 has a detail where you can see the opilio using its fangs to cut small particles of the biscuit.

Video 2

Defensive strategies: Some respond to predator attacks by feigning death (thanatosis). Bobbing, which consists in vibrating the body making hard the identification of the exact location of the body, is also used by many species particularly the ones with long legs. Opiliones can lose one of the legs (autotomy), which continuously keep twitching after it is detached. This is because there are pacemaker neurons located in the femur that become active with any change that breaks the communication between CNS (central nervous system) and these cells (as amputation, damage to the cells…). The twitching has been hypothesized to function as defense mechanism by keeping the attention of a predator while facilitating an escape. In spite of this benefit it also has costs: mobility, foraging abilities and sensory perception can be reduced. [2] The opilion in video 1 has lost two legs on its right side. I suspect that while it is using one of its left leg to check the environment, this ability is reduced on the right.

2. Female of 1 (? ...help! :) )
2. Female of 1 (? …help! 🙂 )

Opiliones have a pair of prosomatic (anterior to the prosoma or cephalothorax that comprises the head and torax) defensive scent glands (ozopores) that secrete a peculiar smelling fluid when disturbed. This chemical defense seems to be effective in repelling some predators. [3] The great majority of opiliones reproduce sexually (some species reproduce asexually by parthenogenesis).

Interestingly, the opiliones may have been the first group of arthropods to evolve an intromittent organ. Parental care may take many forms: chose of oviposition sites or preparation of nests. Although maternal care is widespread among arachnids, Opiliones are the only order in which some species preserve exclusive parental care.[2]

There is more specific info about the opiliones’ CNS which i would like to understand better and I’ll try to come back to this in the future. Help to identify the species from the photos is most welcome…also to the one in the previous post which seems a short (or shorter) legged one.

 

References:

[1] Kury, A.B. (1999-2010) Aracnolab – Aracnologia MNRJ. Museu Nacional/UFRJ website. Online at: http://www.museunacional.ufrj.br/mndi/Aracnologia/aracnol.htm

[2] Harvestmen: the biology of Opiliones, edited by Ricardo Pinto-da-Rocha, Glauco Machado, Gonzalo. Giribet, Harvard University Press, ISBN 0-674-02343-9 http://books.google.ch/books?id=pbdpSKHkKDIC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

[3] http://ecologia.ib.usp.br/opilio/pdf/Machado%20et%20al.%20%282005%29.pdf [#] Another book that looks interesting: Harvestmen: Keys and Notes for the Identification of the Species, By Paul D. Hillyard, John H. P. Sankey http://books.google.ch/books?id=2PcUAAAAIAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false [#] http://ecologia.ib.usp.br/opilio/opilio.html

Backyard Friends …a new set of story tales

Last year was another discovery year 🙂 Now from the garden. My backyard was an authentic zoo. We let the wild plants grow and all the little bugs and whatever animals loved it. And I loved that they love it!! There is also a cat coming once and a while. During August, my boyfriend convinced me to buy a biscuit box to blackmail ‘her’ (to me all the nice animals are female …:p), for ‘her’ to come more often. The cat did not like those biscuits that much, especially after they all got moisty during the evening, after raining!

Lesminhas
 
Our Backyard Friends had a party! Actually I think the slugs started it! During the evening opiliones, slugs, snails…they came and loved it! As you can more or less imagine by looking at the pictures.
 
These animals were quite happy eating all the moisty biscuits. (I’ll go into details later, with a video)
 
However, this got me worried. It seemed to me they could not stop eating that stuff..and we could definitely see the slugs growing larger…I honestly thought they could explode!
 
Lesminhas
Lesminhas
 
Backyard Friends ...a new set of story tales
Opilião
 
 
The funny part was that in the end the cat did not come more frequently… Plus….i fell in love with both the opiliones and the slugs..

 

Little ones

 
This is a continuation of the spider tale :)
 
Going back to those days when I kept myself observing and rushing to my bedroom window to check for Madame Diadematus…
Me and my spider…. By observing ‘her’ I end up thinking of how solitary she was and … thinking further, if spiders have a social life.
 
Of course I turn to the web, did my search and in fact they do exist.
1st I landed on wikipedia, on Social spider page.
3rd on a couple of labs doing research on this subject, for example http://www.spiderlab.dk/social-spiders.html. Although a rare trait among spiders, it can happen! There are a few species that indeed share web, nests, capture preys together and there is also evidence of cooperative breeding. Some other species are not permanently social but can have a social period in the juvenile stage, before dispersing. (source: the last link has some references, e.g. Whitehouse & Lubin 2005)
 
I will not go deep into any of this for now. I just want to share some of what I observed. More information can be found by following the weblinks.
 
Going back to my window:
 
Little ones
Little ones’ clusters
After some time, Madame Diadematus disappeared. I was also away for some time, so I lost track of events. … but one day in April the eggs hatched. One day they were born…they must have :). If you look at the pictures you can see groups of tiny spiders clumped together.
 
These little spiders were grouped together for some time, a few days. Every time some strange ‘foreigner’ web vibration occurred they would disperse a little and then when all was calm they would form the groups again. I did not check whether the newly formed groups would keep the same individuals or if they would randomly regroup again…would be nice to check on that! Although I have to say that the spread was not huge…. I thought to myself that this is a kind of social gathering. …or not? Well as aforementioned… they do aggregate right after hatching. I would speculate that …yes, it seems so…but this should be properly tested  😉
 
Little ones
Cluster closer look
They were together I suspect for protection (?). Maybe by grouping themselves they can simulate a larger body and predators (maybe birds? I do not know if they have predators though…) would ‘think twice’ (?).
They were yellow and had a black stain (see pictures). On the other hand would this can attract insects(?) Not sure of what/if they ate!
 
Little ones
 

 

One day the little ones spread and went away. A few days (maybe weeks) later I realize that I have two spiders…one on each corner of my window… probably from those little-one’s groups.
 

 

 
 
  More information and photos:
  1. http://www.nicksspiders.com/nicksspiders/araneusdiadematus.htm
  2. http://animaldiversity.ummz.umich.edu/accounts/Araneus_diadematus/#c1ad1e3a3c216528bde91e44bf5a7f67