Friday, 4 September 2015

Wood White [life cycle, 1st and 2nd broods]

A study in 2015 of Chiddingfold Wood's Wood White life cycle found that the ovum of both broods are laid singly, mostly on Bird's-foot Trefoil,  then Meadow Vetchling and  lastly Tufted Vetch, and normally on the underside of the chosen leaf.  I took three ovum laid by the females of the 1st brood and, found that they all hatched  between 11-12 days. The ovum when first laid were an off white in colour, turning a yellowish colour after a few days, [but this could possibly be caused by light refraction]. 24 hours before the tiny larva emerged i checked and photographed an ovum which is transparent at this stage and, you are able to see the larva within the ovum, it's mouth and the black spots on the caterpillars cheek. The mouth of the Larva was clearly visible which was red, which told me that the larva should be orange,  [from  previous observations of the ovum at this stage]. Which confused me somewhat as the egg [again from previous observations] should have been orange, or so i thought, but wasn't. So after some experimenting with camera settings and light [photographed totally in the shade] to my complete surprise the photograph of the ovum was pink in colour, a first for me, and again could be the result of light refraction. All the same i decided to except the pink colour of the ovum as being correct and, to await the outcome of the larva emerging  and it's colour.

I then took 7 ovum that the 2nd brood female Wood Whites had laid. All these eggs hatched between 10-12 days. After examining and photographing some of the ovum 24 hours before hatching, the mouth again was red, and the black spots on the cheeks of the tiny larva were also visible through the transparent membrane of the ovum. But this time all the eggs were orange in colour meaning the larva should be orange too. And on emerging all caterpillars were indeed orange. The resulting butterflies from these eggs will emerge next spring, late April, early May 2016. I watched a female Wood white ovipositing on some Tufted Vetch on the 22nd August 2015 just before a colder/wet spell
of weather. The larva which was clearly ready to emerge, still hadn't 15 days later when i checked the egg on 6th September which was a lovely hot day. The larva within the ovum was orange with a red mouth. So the weather does play a significant part in exactly how long the larva takes to emerge from the ovum, whether its hot, cold, wet etc.

Last year [2014] and the year before [2013] i witnessed two ovum hatching, [both eggs being laid by 2nd brood Wood White females] one on 22nd August 2014 which was orange and had a red mouth, the same as the larva that emerged from ovum taken this year, [2015] in the same corresponding period for each year. The second larva hatched on 5th September 2013 and was a beautiful white in colour, with a black mouth and black spots on it's cheek.  The white larva is the only one i have seen, and because of all the other results from this study, must/could be a fluke/miracle of nature, a one off that i was fortunate enough to see and photograph for the record.
This ovum was laid by a 1st brood female Wood White one of three i took from the wild.  This is what it looks like 24 hours before the larva emerged. You can clearly see the red V shape mouth and the black spots on the caterpillar's cheek are both visible through the transparent membrane of the ovum
This tiny 1st instar Wood White larva about 1.5mm in length has emerged from the pink ovum. It has a creamy coloured body with a very faint tinged orange head. The colour green to the body is caused by light refraction 
This ovum is one of the 7 i took from the wild [2015] that was laid by a 2nd brood female Wood White and, the
resulting butterfly will emerge late April, early may 2016. This photo depicts the colour of the ovum/larva 24
hours before the tiny larva emerges
This 1st instar larva which has also just emerged  from one of the three ovum  i took has the same creamy
coloured body, [again with a green tinge to the body caused by light refraction, but much lighter than  the
other larva above this time] and the head is quite visibly orange. This photo of this particular larva is i
believe, far more accurate colour wise. The third larva was very similar.

Light Refraction does affect the colours of both the ovum and the caterpillar at this very early stage and,
i have worked hard to find the correct colours of the ovum and larva and believe all the colours are as
close i can get to the true colours in all these photos.

This ovum is also one of the 7 eggs i took from the wild,  laid by a 2nd brood female Wood White [2015] and
unusually has been laid on the top of the leaf. Again  this photo was taken 24 hours before the caterpillar
emerged. It takes a bit of doing finding the mouth as you can not see it with the naked eye, but i managed to find it
again in this photo. Showing an orange bodied larva with a red mouth through the transparent membrane of the
This 1st instar Wood White larva emerged 24 hours after photographing it in it's egg in the above photo, and is
completely orange in colour,. The larva is very close to the empty egg it has just emerged from. Sometimes on
emerging the Wood White larva will eat the egg, sometimes eating all of it, sometimes partially, and sometimes
they just leave it all together.
This is another larva that has just emerged and like the others, is completely orange apart from the slight green
tinge to half it's body, which again is caused by light refraction. 
I witnessed this orange larva emerging, and photographed it on 22nd August 2014

This larva is the only white one i have found and it was the first Wood White larva i had seen, and thought all
 Wood White larva on emerging were this colour. Photograph taken on 5th September when it hatched. But all
the results in my study this year have proved it to be a one off.  

Once the tiny 1st instar Wood White larva from both 1st and 2nd broods had reached the age of 3 days they were the same in colour for all the instars. Some of the larva took longer to reach the 5th instar stage and ready for pupation, especially the offspring from the 2nd brood. Taking between 21-23 days for the offspring of the 1st brood and, 24 days [ovum laid 17th July, hatching 27th-29th July] and, between 39-50 days [ovum laid 29th-31st July, hatching 10th-12th August] offspring of the 2nd brood Wood Whites. 

1st instar Wood White larva, 3 days old.
Late 1st instar larva having grown to big for it's present skin
is ready to moult
2nd instar larva having just moulted, with it's old face mask
attached to it's back.
Late 3rd instar larva
4th instar Wood White larva.

Final instar Wood White larva has just started to make it's Cremaster
in which to attach it's abdomen to.
Wood White 5th and final instar larva, having already attached itself
to the Cremaster, is now attaching the Girdle to it's mid-drift and the stem of the
Bird's-foot Trefoil.
Wood White final instar larva ready for pupation.
   Wood White pupa, offspring of the 1st brood, [from 3 ovum taken from the wild]

The pupation period lasted between 10-13 days, all 3 pupa were between 15-16mm in length. Producing 2 males and one female.

Day one, 16 hours after pupation began.

Day 3
Day 6
Day 7, the white of the wings starts to show through
the transparent membrane of the pupa.
Day 10
Day 12. Quite a transformation between day 10-12, the butterfly
within the pupa is now full formed and, clearly shows that it is a
well marked female, the antenna being black. If it was a male the
antenna would be black and white. The female Wood White emerged on the 13th day.
 Wood White pupa, offspring of the 2nd brood.

The Wood White pupa that is the offspring of the 2nd brood over winter at this stage of the life cycle, with the butterflies starting to emerge late April, early May. The pupa were 17-18mm in length, 1-3mm larger than the offspring pupa of the 1st brood.

Day one

Day 4
Day 7, the pupa overwinters at this stage of the life cycle,
with no further development to the pupa until the Spring.
This coloration is unique to the offspring pupa of the 2nd brood Wood Whites.

All photographs are the copyright of Nick Broomer.