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Here's some behavior I've been hoping to capture for a while! These Callobius pictus males had a quick dispute on one of the sheds in my yard. The shed is home to many C. pictus and C. severus spiders, especially the former right now.

The larger spider (left in the pictures) was crawling up along one of the corners while the smaller one was milling around higher up. The males seemed to notice one another from a distance of about 10 cm and they began moving in rather abrupt, jerky motions towards one another. When they were close enough, they stretched out their front legs out to the sides and made contact with the other spider's similarly extended legs. Then they came together and tussled for a bit, also grappling with their second pair of legs. The actual physical contact lasted only about 10 seconds. The smaller spider (right in the pictures) retreated and neither seemed any worse for wear.

The images of the dispute are in REVERSE chronological order. The individual close-ups are of the smaller spider on the right following the encounter.

I've seen similar behaviour in C. severus before, although the severus duel I photographed was lengthier with multiple scuffles:

https://bugguide.net/node/view/795954/bgimage