Stromatopelma calceatum - the use of the male scopulae brush during mating

Having witnessed a pair of common feather-leg baboon spiders mating (Stromatopelma calceatum), this article explores a theory on the use of the scopulae brush which the male acquires on the metatarsus of leg 1 following his maturing moult.

On its maturing moult the male develops a distinct round brush of stiff setae on the metatarsus of the front pair of legs, which is referred to as the scopulae brush (a key taxonomic feature in the Stromatopelma genus). As soon as the wandering male comes into contact with the female his first priority (after signalling to the female by drumming with his palps) is to manoeuvre his first pair of legs between the females palps and chelicerae and position his scopulae brush firmly between them. The brush sits perfectly between her palps and chelicerae while the lower part of the metatarsus and tarsus curl over the top of her carapace and supports the females' weight as she bends back to assume the mating position. As this genus possess no tibial spurs for securing the female fangs, I believe that rather than holding her fangs out of harms way, the Stromatopelma male uses scopulae brush to actually squeeze them together thus preventing him from attack. As the female prepares to receive the male, she can be seen moving her chelicerae in a chewing motion in readiness for the insertion of the male brush and it also acts as a very effective wedge when he supports the females weight.

Mating observations: During May 1993 I purchased a sub-adult specimen and, as I was unable to correctly identify the sex due to damaged cast skins, I was pleased to discover that it had moulted out into a fine adult male (maturing moult: 9/9/93).

A mature female was bought at the A.E.S. Show from Paul Carpenter and after placing her in a temporary tank for mating, the first pairings occurred as follows: -

13/10/93 (1st): On inspection of the males container, there were signs of a recently dismantled sperm web and therefore a pairing was attempted. The female hadn't eaten since being housed in her temporary tank as she wasn't interested but had settled quickly and spun some silk round the sides and over the cork bark.

The males container was placed upside down on top of the females (34 days from maturing) and after a little persuasion he entered at approx. 7.45 p.m. He immediately walked down the side and towards the female, which sat huddled near the bottom, hunched against the side and the bark, facing downward. On contact with the female, the male began the characteristic drumming with his palps on the glass and tried to climb around the sleeping female (it must be noted here that the male approached the female with no apprehension whatsoever, emphasising the males' eagerness to mate). The male impatiently pushed beside the female trying to curl his first two pairs of legs round her, drumming his palps constantly. Eventually the female moved and quickly turned to face the male and vibrated her front legs in response to the males drumming. The male moved in and placed his front legs between the females palps and chelicerae and pushed his scopulae brush into position, the lower part of his metatarsus and tarsus curled onto the females carapace providing support for the weight as she prepared to bend back into the mating position.

The female then bent her cephalothorax backward as far as possible but due to her awkward position the male couldn't get his palps into place so, after a little persuasive drumming, he beckoned the female to move up the tank side and she followed him, vibrating her front legs invitingly. This procedure continued a further three times until the pair were close to the top of the tank and eventually the female was in a good position to expose her epigastric furrow. The male then moved forward and inserted his left palpal bulb. On insertion the female jerked violently forward and reacted in the same manner when the second palpal bulb was inserted for a split second. Immediately the second palp was removed and the female moved away rapidly and returned to her resting position as if nothing had happened. The male casually crawled out of the tank and was replaced in his container and the females' epigynum was swollen for some time after mating. Mating ended at approx. 8.15 p.m.

19/10/93 (2nd): This pairing was different to the first with respect to the aggression of the female and the confidence of the male.

The male was introduced and he proceeded to enter and started wandering round her tank as if knowing exactly what to do. This time he approached her from behind the cork bark and he climbed onto the opposite side of the female, he drummed his palps slightly and she responded immediately by turning quickly in a very alert state. The male remained motionless for a short time but soon moved round the bark and on touching the females' legs, he began the usual courtship drumming and stroking of the legs. The female was eager to mate again but didn't respond by vibrating her front legs as she did previously. The male made his way round until he was facing her and as they were in the same awkward position as before the female moved instinctively round the bark into a better position (do spiders have the capacity to learn from previous encounters?). All the while the male drummed and worked his front legs and scopulae brush into position with the tips of his legs touching her carapace. The male alternatively inserted his palps but as soon as the second palp was removed, the female suddenly became aggressive. She grabbed for him with her front legs but he pulled away quickly and ran with lightning speed to his waiting box above. The female became very nervous at this point and began running around the tank looking for a place to hide which is very unusual, as she has always been quite placid. Eventually she settled in her usual pace and the male was removed. This mating only lasted approx. 10 minutes.

Point to note -
(1) Aggression of the female. Increased aggression of the female was obvious when mating was completed and whether the female actually wanted to eat the male or just scare him off isn't known. On the first mating the female was very passive afterwards, which makes me believe that the second time she agreed to the pairing only to make sure successful sperm injection had taken place.

24/10/93 (3rd): The male entered the females tank as usual and inside, he moved very cautiously towards the female which was in the normal position as before. On coming into contact with her, he touched her rear leg with his first leg and drummed with his palps very briefly. She made no movement so the male remained perfectly still behind the female with his tarsus touching her tarsus. After a long period without movement, the female moved her leg away from him and after another long pause, the male slowly moved back, climbed the glass very slowly and returned to his box and he was removed. There are three possible explanations for this behaviour: -
(1) The male wasn't ready to mate and hadn't recently built a sperm web.
(2) He recognised the female and after her previous aggression, he thought it wise not to attempt to mate.
(3) The response of the female as she pulled away may have signalled to him her unwillingness to mate again.

No further pairings were attempted and the female was housed in her permanent tank but unfortunately, no fertile egg sac was produced before she finally moulted.



www.giantspiders.com