Rearing the Mediterranean thorn back spider Cyrtophora citricola

Collecting
As its name suggests, C. citricola can be found throughout the Mediterranean region and I was on holiday when I collected the egg sacs in the Algarve (Portugal). Large numbers of adult females can usually be found living communally on bushes during the summer months and collecting the eggs is a simple affair as they are laid in the centre of their large webs.

Description
The adult female is about the size of our garden spider (Araneus diadematus) and colour varies from very dark brown (almost black) and white to a very pale cream and white zigzag pattern with six thorn-like protrusions. The carapace is covered with grey/brown tufted hairs and legs are cream banded with brown, again similar to A. diadematus. The spinnerets are circled with a star-like pattern and there is a striking orange/red stripe running through the centre of the sternum. The male is much smaller than the female, so much so that it could easily sit on the females' carapace. The protrusions on the abdomen are not as obvious on the male and the colour is generally black. Along with the sternum stripe, the pattern around the spinnerets is also bright orange/red with the carapace and legs being very dark grey to black.

Web Construction
An adult female will build a web reaching a diameter in excess of 12" in its natural habitat which can cause a problem in captivity if space is at a minimum. Fortunately, a specimen will adapt quite easily to the amount of space given for web building. A few basic requirements should be met and this consists of a container that is taller than wide and they seem to prefer round rather than square. Food storage jars are ideal as long as a new lid is made to prevent damage to the web whilst feeding. No substrate is required but a thin leafed twig should be firmly fixed to the side of the container and be arched across the top to aid construction. The web itself is a beautiful cage-like structure and the spider is always view as it sits underneath the tent-like centre of the large spiral. This resembles a horizontal orb web and is surrounded by an irregular mesh of threads. The web is not as efficient as the vertical orb web when it comes to prey capture as the spiral is not sticky, and C. citricola relies on insects becoming entangled in the above mesh threads and falling onto main spiral. Nevertheless a great deal of success is achieved due to the spiders amazing speed and agility underneath the web. After being introduced into the container C. citricola will spin the mesh of construction lines within the first few nights but actual building of the spiral is not usually triggered unless prey is known to exist in the given area. Therefore, small insects should be dropped onto the web and spiral construction will take place the following night. Kullman (1972) suggested that the Cyrtophora web represented an immediate seep between the sheet web of the Linyphiids and the orb web of the Araneids with the tilting of the central sheet. However, Lubin (1973) believed that the web is derived from the orb web which is more likely as Cyrtophora is known to he an Araneid. If too little space is allowed for adult female web building it will sometimes only spin a section and sit off-centre so it is advisable to keep at least one adult in a large enough container to observe web structures. As mentioned earlier, web making takes place during the night and is a very frantic affair compared to that of the average orb weavers (the average number of split radii is much higher, around 200). Only on rare occasions will a specimen actually replace an existing web if enough food is available and web repair seems to be more favourable. Repairing does not follow the pattern of most orb weavers that join the radii, instead holes are filled with a mesh of irregular threads and eventually the whole web may be an untidy mass of patched holes. If web replacement does occur, it is obvious with the appearance of a lump of wool-like web below the spiral. Again, this is unlike other orb weavers which eat their dismantled web.





Web efficiency and feeding behaviour
The web of C. citricola is not as efficient as that of any orb weaver but nevertheless, a great deal of success is achieved depending on the prey item offered. When the spiders first hatch the webs they build are small (approx. 50 mm in diameter), and finding food items which are small enough is a problem. Even tiny prey such as semolina creatures (Liposcelis bostrychophilic) are prone to falling through the un-sticky web of C. citricola but, as the spider grows, it will take a variety of food such as crickets, blow flies, waxworms and mealworms, etc.

Moulting
C. citricola moults in the usual Araneid fashion in the mesh of construction lines above or below the main spiral and the exuvium is left there while the spider returns to the web. Apolysis (pre-moult) is short (around 2 days) with feeding usually resuming approximately 2-3 days and in the early stages moulting can be quite rapid, sometimes as quick as 3 days apart. On average, it takes eight moults to reach maturity.

Water requirements
The web should be sprayed lightly with tepid water for drinking purposes, but C. citricola will use the water to eagerly clean itself as well as to drink. As a rule, however, spraying should be avoided until the spiders are of a reasonable size as many drown in the small drops of condensation that can occur.

Sex determination and mating behaviour
With a number of individuals of C. citricola determining the sex is an easy affair as the size differences are obvious from an early stage. If the adult female is ready to mate when the male is introduced, she will eagerly advance towards him (almost chasing) then he jumps to the ventral side of the female's abdomen and fixes one palp into the epigynum. The male then falls backwards and his abdomen rests underneath the female's prosoma. Then she seizes the males' abdomen with her chelicerae and starts feeding on him. This process is necessary because of the size differences between the sexes and if the female didn't grab the male, he would most certainly fall off, making copulation impossible.

Egg sac construction
When the female's abdomen is swollen with eggs, she will hang in the centre of the web with all of her legs stretched out approximately 3-4 days prior to egg case production. The egg sac is laid during the night in the mesh of construction lines above the main spiral which begins with a flat circular disc of fluffy orange/tan threads which the spider spins from underneath. Next, a small circular depression is formed in the centre and a cylindrical wall is added. The eggs are deposited inside and the outer covering is finished with a mesh of loose threads. The female guards the egg case adamantly and if the container is opened at any time, she will run to protect it, wrapping her legs tightly around it.

Longevity


Adult female's life span is around twelve months and death occurs after mated females have produced two, sometimes three egg cases. Unmated females, however, may live 18 months or more waiting for a male to appear.

References: Biology of Spiders - Rainer Foelix - Harvard University Press, 1982.



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