francesco-ghinelli 的最愛

A unique and interesting find…..
On 1/5/20 I found something that completely blew my mind. I was at a local balancing pond on the Coopers Edge Estate SO874163 when I came across an Alopecosa pulverulenta female with her egg sac. It looked like she was in the process of rotating the sac as it was positioned under her sternum and being held in her chelicerae (photo 1). Her imitation of that other grass dwelling species Pisaura mirabilis, was very impressive indeed. After taking a couple of photographs the spider ran off, although in a rather ungainly fashion due to the way she was holding her egg sac. It was then that I noticed that rather than one sac, the spider was actually carrying two (photo 2). To say I was shocked is an understatement and I stopped her disappearing into the undergrowth by blocking her path with my hand. She then changed direction and started to head towards the shorter patch of grass that I had originally seen her on. This helped me twofold by making it easier for me to photograph, (it’s no easy chore chasing Lycosids through grass, especially with my knees) and also there was less chance of me losing the spider. I took several photos of her in her natural habitat (photo 3 & 4) before collecting her and popping into a container. I then packed up my camera equipment and made the five minute walk back to my home thoroughly excited with my find. Once home I started to look carefully at the egg sacs under a 10x magnification hand lens. From experience I can see that the white sac was produced by A.pulverulenta as it has the shape and structure of a golf ball which is typical for a freshly produced egg sac of that species. Initially, I believed the second sac and obviously the older one, was produced by a Pardosa species but must confess to having reservations about this now. Both sacs have been welded together with silk and the fresh sac is indented by the older sac. I can only surmise as to how she ended up with two egg sacs. One theory is that the A.pulverulenta found the older discarded sac shortly before she was due to produce her own sac and the innate maternal instincts kicked in thus causing her to attach the sac to her spinnerets. Whatever the reason for her having two egg sacs, this seemed a very unique find. For the next several hours I searched through the literature regarding this behaviour or even a similar image of a Lycosid with 2 sacs but this proved fruitless. What my search did throw up was a remarkable image of an ichneumon wasp, Gelis species emerging from a Pardosa species sac that was photographed by Chris Ernst in the Yukon territory, Canada. Why would this seem remarkable to me? Well, after studying the egg sacs and looking at the photos I had taken, I noticed two tiny holes in the older egg sac (photo 5 & 6) which looked remarkably similar to those in Ernst’s photograph (Ernst, C. 2012). From my experience, these holes were not caused by spiderlings emerging and besides, it would be far far too early for emerging lycosid spiderlings if we consider the egg sac was produced this year. . I also did not believe that these were caused by wear and tear as the lycosid egg sac is extremely tough and durable. Was the Pardosa sac discarded due to parasitoids? If so, the two small holes would suggest that the progeny of the parasitoid had emerged and the sac was now empty. An interesting study by Joe Bowden & Chris Buddle showed that in the Yukon territory, Pardosa species egg sacs are relentlessly parasitised by Gelis species (Bowden & Buddle 2012). Whether the older egg sac that the A.pulverulenta is carrying had been paraitised remains to be seen and although I have been very tempted to remove the sacs to investigate I have decided to leave them be until the young spiderlings emerge from the fresh sac. Until that time, the A.pulverulenta has been set up in a cosy enclosure.

Ernst, C. 2012 : The Wolf Spider Parasite - The Bug Geek.
https://thebuggeek.com/2012/10/19/photo-friday-wolf-spider-parasite/

Bowden, J J. & Buddle, C. 2012
Egg sac parasitism of Arctic wolf spiders (Araneae: Lycosidae) from northwestern North America.
The Journal of Arachnology Vol. 40, Issue 3 (Nov 2012), pg(s) 348-350