Whilst watching our garden pond on Saturday it became clear that something odd was going on. There was one male Four-Spotted Chaser (FSC) and one male Broad Bodied Chaser (BBC) holding territory on opposite sides of the pond. A female FSC arrived, mated with the male FSC and then laid eggs, accompanied by the male. Then what looked like a female BBC arrived (fatter body and bright yellow stripes down the side). But we assumed it must have been an FSC because the male FSC mated with it. But this was not followed by egglaying. It happened several times and during the last prolonged and anrgy coupling it was clear that the female was trying to get away from the male which she did, eventually. Then after a few minutes the female came back again and this time the BBC spotted her, mated with her succesfully for just a few seocnds and she then laid eggs, accompanied by the male BBC.
So it seems the male FSCs, in their enthusiasm will try to mate with other species.