Thursday, 31 May 2012

Catching up

The good weather has continued, which means that I'm taking hundreds of photographs. Identifications and image selection are taking up a lot of time, so I have quite a backlog.

But tonight I got a very rare opportunity to make a feature of a single species in my post, so here it is:

Ladybirds start off as eggs and then hatch into larvae that go though 3 - 4 stages (instars), shedding their skin as they grow. Their sole food is aphids, so judging by the number of larvae and pupae I found tonight, a vast number of aphids have been consumed this spring.

Early larvae of the 7-spot ladybird are dark with yellow or orange spots:

7-spot ladybird larva, early instar
The final instar larva is, however, grey:
Final instar 7-spot ladybird larva
When the larvae are fully grown and ready to pupate, they begin to curl up with the head down and the tail tucked in:

7-spot larva about to pupate
The larva then begins to change colour as it pupates:
7-spot larva during pupation
(note the yellow under-colour shining through the thin skin)

The outer skin is shed and pushed to the rear of the pupa by means of several quick thrusts of the entire body (the shed skin can clearly be seen at the rear of the pupa):

Fresh 7-spot ladybird pupa

After a short time, the pupa hardens and takes on a darker colour:

7-spot ladybird pupa

And after a few days:

Adult 7-spot Ladybird

I have never seen such a wide range of stages of one species in one place at one time. Our exceptional spring weather has clearly been beneficial to the 7-spot at least.


Toffeeapple said...

A marvellous story, thank you! Fascinating stuff.

Gill said...

Fascinating - is that a sequence of the same individual?

do other beetles pupate? (Ladybirds are a type of beetle, aren't they?)

21stcenturynaturalists said...

Fabulous pictures, they illustrate the metamorphosis perfectly! Unfortunately I found a breeding spot for the invasive Harlequin Ladybird here in Cork city about 1.5 years ago so the seven spot could be soon under threat.

Stuart said...

Those photographs were all of separate individuals, although I could see all the specimens without moving my feet. I watched as one individual shed its final skin, but the movement was far too fast to catch on camera. (Grey skin, violent backward vertical jerk of the whole body, yellow skin, in probably 0.5 of a second). Ladybirds are most certainly beetles and other beetles pupate, too. The hard shell of beetles has evolved from what were originally two outer wings. These elytra (singular elytron) have hardened and become a protection for the two remaining inner wings. The inner wings are folded away for storage under the elytra when not in use and are surprisingly large when deployed. When the beetle has finished flying, it folds and pleats the wings using hooks under the elytra. You can watch as the wings slowly disappear under their hard covers. Again, deployment is explosively quick, with a great deal of wing appearing as if out of thin air in fractions of a second.

Caroline Gill said...

An absolutely brilliant and fascinating post, Stuart, illustrated with great photos. I wonder if you have come across any Ladybirds with damaged elytra, due perhaps to frost or other factors? I have seen one or two cases of Ladybirds affected by the parasitic wasp.

Stuart said...

Caroline: yes, I have found ladybirds with elytra just like yours, and also with missing spots, extra spots, large spots on one side and small spots on the other, and I once found a melanistic 10-spot where the amount of black exceeded the amount of red, making it look as if it was a red-spotted black beetle. I have never found the parasitised ones, but it isn't for lack of looking.