Diving Beetle pupa

[King Edward]

Found two of these yesterday, shallowly buried in damp earth beside the pond. Length is 15 mm. I think it's probably Colymbetes fuscus, or if not then Acilius sulcatus - there were quite a lot of larvae of both species in the pond earlier in the summer, which I haven't seen recently so presumably they've all pupated by now. There have also been at least two Colymbetes adults swimming around over the last few days, which I don't think were present until recently, so it seems most likely that these are recently emerged individuals.

While I wait to see what emerges, does anyone know for sure which species this is?

[Ukwildlifeo]

Can't help with the species, but what a cool find!

[Wild-Woman]

Can you keep up updated with this one. Very interesting.

[King Edward]

The two of them are currently sitting in a container with some damp earth - no change yet.

[Jason Green]

Originally Posted by King Edward

The two of them are currently sitting in a container with some damp earth - no change yet.

Are they 'Shallowly-buried' to the same depth you found them at originally, in their new container?

[King Edward]

No, they're just sitting on the surface of the earth so I can keep an eye on them. They're in a plastic ice cream container with holes in the lid, so in the dark. Each was originally in a sort of small chamber in the earth, which was broken open when I dug them up - I'd been weeding out a bramble root when I discovered them. If they were just reburied in the soil, the adults might not have enough room to full expand their bodies when they emerge.

There's a photo of a Dytiscus marginalis pupa here.

[Jason Green]

If they were buried when you found them, it's probably best you replicate the exact circumstances - inc. burying them in case their emergence is based on soil temperature/dampness.

I suggest you transfer them to a clear vessel, such as a jam-jar. To monitor their progress, you could always bury them at the edge so they touch the clear glass wall (but keep this part in the shade when not viewing). I would advise they be kept somewhere that is of a similar temperature to outside, too.

[Matt Smith]

Originally Posted by Jason Green

If they were buried when you found them, it's probably best you replicate the exact circumstances - inc. burying them in case their emergence is based on soil temperature/dampness.

I suggest you transfer them to a clear vessel, such as a jam-jar. To monitor their progress, you could always bury them at the edge so they touch the clear glass wall (but keep this part in the shade when not viewing). I would advise they be kept somewhere that is of a similar temperature to outside, too.

The conditions they are being kept in after being dug up are fine. Humidity is the key thing, they need to be fairly moist so that they do not dessicate. Having reared an awful lot of "exotic" beetles, the danger in reburying is that there is not enough room to expand the wings and elytra. Most beetles make a pupal cell so they have this room - if you bury them again dirt may interfere.

[King Edward]

Originally Posted by Matt Smith

the danger in reburying is that there is not enough room to expand the wings and elytra. Most beetles make a pupal cell so they have this room - if you bury them again dirt may interfere.

This was my concern exactly - the pupal cell was evident on the first one I saw although I broke it picking it up, and it's also very visible on the Dytiscus photo I linked to. There's been no change in the pupae so far, although there are adults around of both candidate species so I'm hopeful that emergence will take place before too long.

[Wild-Woman]

Fascinating thread. There's very few people that have had the privilege to witness this sort of thing first hand. Certainly a first for me. Thanks for keeping us updated.