Unexpected aggression in the male O. aureotibialis during mating

Fourteen months after obtaining my specimen of the Thailand black Ornithoctonus aureotibialis, I was pleased to discover that it had moulted into a fine mature male. Males of this species undergo a vast change in appearance on their final moult and the colouration changes dramatically from the usual brown / black of the female. The carapace obtains a slight pink tinge and the legs turn to fawn except for the tarsus which is very dark brown to black; the femora are black and have a distinct purple sheen; the abdomen retains its characteristic chevrons and is unusually quite plump. The males mating spurs differ slightly from many tarantulas as they possess a single blunt spur rather than a hook. A few days after moulting, the male was re-housed in a clean box in order to observe sperm-web building behaviour and this commenced approximately 10 days later A wide band of dense silk was spun from the floor of the container at a 45o angle and attached to the side. The male spent many hours crawling round and underneath this web, adding silk to it all the while and everything appeared to be going well - or so I thought!



The next morning a strange sound was coming from where my spiders are kept and, on inspection, I observed the mature O. aureotibialis female drumming on the side of the container. The males' box was nearby but he didn't seem to notice her presence. This was unusual as he wasn't signalling to her and for some unknown reason, he still hadn't successfully completed his sperm-web. Explanations for this behaviour at the time were that she was obviously eager to mate and the box in which she was now housed previously contained the immature male. Maybe there were some slight traces of him still present even after it had been thoroughly cleaned out and, meanwhile, the male continued to add yet more silk to his sperm-web. This was strange as the process usually only takes a few hours and this behaviour continued for a further week The following night, the males box was paced on top of hers and they were observed (and heard!) signalling to each other for several hours. The male still hadn't finished his sperm-web and a conclusion was made that it wasn't a sperm-web but more of a retreat. On this supposition, a pairing was attempted.

Their two boxes were opened and placed side by side. The male was gently coaxed onto the inside of her box where he remained motionless for the next 10 minutes. He then climbed from the side onto the floor and again, remained still until he eventually walked round the container and came into contact with her. She immediately moved forward very quickly with bared fangs and her front legs raised and this startled the male who quickly drew back with his legs raised. They touched for a few seconds, then separated. Next, from a safe distance, the male began signalling by vibrating his body and she eagerly responded by drumming loudly on the substrate. This behaviour continued for the next 30 minutes and he backed himself into a corner of the box, eventually stopping signalling altogether. After some time the female moved away from him as if she'd had enough of his teasing and he was removed.

The males unwillingness to mate was probably due to the fact that he hadn't charged his palps and wasn't ready. He signalled only to prevent himself from being attacked.

Realising that the male hadn't successfully completed a sperm-web due to lack of space, he was re-housed in a larger box. Within the first night, he achieved this and the next morning, the dismantled remains of the web were obvious.

The first successful mating occurred the next day. He was introduced to the females box and his behaviour was totally different to the previous attempt. After only a few seconds he began wandering, actively searching out the female who was settled in her cave alcove. He came into contact with her webbing and immediately started vibrating his body, signalling to her and she responded by drumming her front legs and palps on the substrate. The male followed her signalling and moved closer to the alcove, vibrating all the time. She sensed his presence and moved out of the alcove until they made contact then he began stroking her front legs while she raised them. She was in a slight depression in the substrate and he didn't like her position but he tried, and failed, to engage her chelicerae with his mating spurs. Moving back, he tried to entice her from the alcove and she slowly followed. Again he moved in but she was still in an awkward position so moving in close, he violently butted his chelicerae with hers as if scolding her for stubbornness! This occurred another few times until he successfully wedged his tibial spurs under her chelicerae and lifted her, drumming with his palps on her sternum. Pushing her firmly back, he inserted his left palpal bulb and after a split second, she jerked back and collapsed on her abdomen almost doubling over as he injected his sperm. They remained still for a few seconds but when he withdrew his palpal bulb, a slight scuffle broke out and they tumbled towards the front of the box. She tried to release her flings from his grip and he found himself in an awkward position beneath her and was reluctant to let go. Eventually she eased back a little as if letting him off the hook and he took his chance. Releasing her fangs, he broke free and ran into the comer of the container where he was removed. The female writhed on the floor for a while, frantically rubbing her underside with her rear legs and moving her chelicerae in a chewing motion. Her epigynum was very swollen after the mating and she sat for a long time with her abdomen raised until she finally gave herself a good clean.

Three further pairings were successful and very similar to the first and a few conclusions can be made:-
(1) The matings were very violent on the part of the male, actively slapping the female on the carapace with his front legs and buffing her chelicerae with his. He must have sensed her eagerness to mate so didn't think there was any risk involved with such a passive female;
(2) Always remember to ensure that the male has enough room to build and complete a sperm-web and;
(3) Make sure the male has charged his palps. It can usually be noticed if he is ready to mate as soon as he enters the females territory. If he doesn't start signalling almost immediately, the chances are he isn't ready and should be removed and my male only survived as the female was so eager to mate and was so submissive.



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