Friday, 11 June 2010

More questions than answers

At least seven broad-bodied chasers have emerged from one of our ponds this year. Of these, I have seen all but two and each of these five was female. Added to the fact that of the dragonflies I've seen in flight none have been male I can conclude that we probably haven't had a male emerge from the pond this year. Not having had a great number of broad-bodied chasers in the garden in the past two years it is likely that the individuals that emerged this year are siblings. I confess I haven't searched very hard to see if this is known to be the case, but for now I'm wondering if all eggs oviposited are the same sex, possibly to prevent siblings from mating with each other.

Of the five individuals that I observed emerging two were unsuccessful. One didn't manage to open its wings at all and the other (below) only managed to unfold three out of four. I don't know for sure the fate of the second individual - I suspect it was either eaten by a bird or else simply died and fell amongst the rushes, but it was definitely sitting in the same position over 36 hours after it emerged and I doubt it could have taken flight. Given that rates of mortality must be pretty high during the larval stage of the life cycle I was quite surprised by this high rate of unsuccessful emergence. Have we just been unlucky or do so few really emerge successfully?

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