John. H's picture

IMG_2501

Observed: 1st March 2012 By: John. H
IMG_2501
IMG_2502
IMG_2503
IMG_2505
IMG_3887
IMG_3897
IMG_3902
IMG_3901
Description:

What came out of this insect casing?
Hi. I have a small garden pond. At the beginning of May last year I came across quite a few of these small black objects floating on the surface of the water. At first I thought they may be seeds, but on closer inspection they seem to be the cast off of some sort of insect that has emerged from them.
I am sorry about the picture quality but as you can appreciate (from the penny) they are pretty small.
O.K. It looks to me as if some beetle type of insect has changed, chrysalis style, into some type of winged insect that has then broken off the head of the now empty shell and then flown away.
Am I right? And if so what is it?
Any answers, as always, greatly appreciated.
John.

Identifications
Species interactions

No interactions present.

Comments

Refugee's picture

Cut one

I would like to see what a lengthwise section looks like.
We need to eliminate umbrella spoke caps or any other manufactured components. The blunt ends look a bit uniform.
I have never seen an insect that can get out of a pupa without splitting it. We will be able to see frass in it if a parasite has eaten them from inside.

Refugee

John. H's picture

Cut one

Hi. Yes I do see what you mean but I do not think they were manufactured.
Unfortunately this was over a year ago and I do not have one now. Having said that I do still have the pond so if you are a patient person and watch this space may be more will crop up in May next year.
Thanks for the interest.
John

Nick Upton's picture

Weevil abdomens

I don't think these are pupae, but the abdomens of dead adult beetles, without the head, thorax and legs. Otiorhynchus weevils are built like little tanks and their "wing covers" are fused, making the whole abdomen a tough unit. Maybe you can look out for live ones next year (gardeners know them well and hate them...) and more corpse fragments and compare!

Nick Upton, naturalist and photographer.

John. H's picture

What came out of this insect casing?

Hi
Please have a look at the up dated photos.
Looked in the pond this morning and here they are again so they are defiantly some sort of insect or its remains.
As you can see, per advice, I took a Stanley knife and tried to dissect one, to er, not particularly pleasant results (YUK!).
I do think that your suggestion, “the abdomens of dead adult beetles” is probably correct.
There are also lots and lots of this other insect in the pond. Any ideas who he is?
Thanks again.
John

Nick Upton's picture

New images

The new creepy crawlies are Freshwater hog lice Asellus aquaticus, actually crustaceans rather than insects, which live as scavengers in freshwater, maybe extracting the mushy goo from old beetle abdomens! If I'm right that the abdomens belong to vine weevils, look out for adults that have overwintered emerging as the weather warms and a new generation hatching in late spring. The adults feed at night on all kinds of things, chewing the edges of leaves, while the grubs live in the soil attacking plant roots. Gardeners hate them... eg see http://www.dgsgardening.btinternet.co.uk/vineweevil.htm

Nick Upton, naturalist and photographer.