Brown Hairstreak (Early Stages)

[Vince Massimo]

Introduction

In 2011 I opened a topic on the Species Forum which documented the process of rearing several Brown Hairstreak larvae. As I had no previous experience rearing this species, the report was submitted in a diary format so that others could comment and offer advice as the project progressed. The original posts can still be viewed here:
http://www.ukbutterflies.co.uk/phpBB/vi ... =37&t=5032
All of this information has now been re-structured and is now presented as a detailed two-part report which incorporates additional information and some previously un-published images. Apart from raising awareness in this enigmatic species it may also be helpful to those people who are considering rescuing eggs before they are lost to aggressive hedge trimming.

This report was updated in 2015 and 2018 and with several fresh images and revised text.


Background

In 2011, during the course of surveying for Brown Hairstreak eggs for the Sussex Butterfly Atlas, I found a total of 3 eggs on severed Blackthorn stems. These were rescued and the resulting larvae were raised to adulthood. During this period of 95 days I observed and photo-documented their development and this is the resulting report. For monitoring and record purposes the larvae were given designations of L1, L2 and L3.

In 2015 I rescued several further eggs and reared the resulting larvae. One of these (designated L4) is the subject of a fresh sequence if images which has been added to the report.

The egg and larva

Two rescued Brown Hairstreak eggs - Crawley, Sussex 24-March-2011

Typical Brown Hairstreak egg - Crawley, Sussex 4-Jan-2011

Brown Hairstreak egg group - Crawley, Sussex 2-Oct-2018

Brown Hairstreak egg group - Crawley, Sussex 10-Oct-2018

Brown Hairstreak egg group - Crawley, Sussex 10-Oct-2018

The larvae were raised under cover, sheltered from wind and rain, on potted Blackthorn plants, but otherwise the temperature, light and humidity levels were kept as natural as possible. The accepted method of dealing with rescued Brown Hairstreak eggs is to tie the severed stem to a living plant and the emerging larva will then crawl into an unfurling leaf bud. Current literature on this species suggested that eggs hatch in late April or early May, but in 2011 I saw a report on UK Butterflies that an egg being monitored in the wild in Sussex had hatched on 7th April. Upon checking my eggs the following morning I found one already had a hole in it but fortunately the larva appeared to still be inside. At that stage I had not yet tied any of the severed stems to the host plants and was nearly caught out by the early hatching date.

It can take a Brown Hairstreak larva the best part of a day to chew a hole large enough in the egg in order to emerge. A thick and tough eggshell is necessary in order to get through the winter, but these properties also appear to protect the developing larva against other external forces. Two of the eggs were badly abraded across parts of their surfaces (possibly due to hedge trimming damage), but nevertheless all three larvae successfully hatched on 9th, 10th and 11th April 2011.

Brown Hairstreak larva (L5) chewing through egg shell - Crawley, Sussex 6-April-2020

Larva (L4) chewing through egg shell - Crawley, Sussex 17-April-2015

Hatched Brown Hairstreak egg (L4) - Crawley, Sussex 7-May-2015

By way of comparison here is an egg which was laid in August 2018, hatched in April 2019 and was still on the plant in March 2020, such is the toughness of the eggshell.

Brown Hairstreak egg (laid 18 months earlier) - Crawley, Sussex 11-March-2020

Brown Hairstreak larva freshly emerged (L5) - Crawley, Sussex 15-April-2015

Although the larvae immediately burrowed into a leaf bud (not necessarily the closest one to the egg), they emerged occasionally during the daytime. They first appeared on 14th April, by which time they were 2mm in length.

Brown Hairstreak larva (3-day old first instar) - Caterham, Surrey 14-April-2011

Brown Hairstreak larva (4-day old first instar) - Caterham, Surrey 14-April-2011

Brown Hairstreak larva (4-day old first instar) - Caterham, Surrey 15-April-2011

Brown Hairstreak larva (8-days old) - Caterham, Surrey 17-April-2011

By day 12 of their development all of the larvae had moulted into their second instar, taking on a different shape, appearance and colouration and increasing to 4mm in length. They were now to be found resting under their respective leaves, although they were occasionally active during the day.

Brown Hairstreak larva (12-day old second instar) - Caterham, Surrey 23-April-2011

After 17 days or so they began to moult into their 3rd instar.

Brown Hairstreak larva (17-day old second instar preparing to moult) - Caterham, Surrey 28-April-2011

Brown Hairstreak larva (18-day old third instar - freshly moulted) - Caterham, Surrey 29-April-2011

After a month they had grown to around 10mm in length and then one (L1) unexpectedly went missing. Although only half grown it had left the food plant for some reason. Fortunately it was relocated two and a half days later and continued feeding as soon as it was returned to the plant. Thereafter all of my plants were netted.

After 35 days the two largest larvae were between 12mm and 15mm in length and all were following the recognised routine of feeding during the night before returning to the undersides of their designated resting leaf during the day. When they changed resting leaves they could be very difficult to relocate, despite the fact that I was attuned to their appearance and only had a very small plant to search. Although the larvae were a paler colour than the Blackthorn leaves and stood out when viewed in sunlight, this is not how they would normally appear in nature. Thus far my photos had been taken from below the leaf, either with the larva moved into full sunlight or with the use of flash. This however is not how a predatory Blue Tit would see them, so I took a series of comparative shots in different lighting levels.

Brown Hairstreak larva (36 days old - in sunlight) - Caterham, Surrey 16-May-2011

Brown Hairstreak larva (36 days old - in daylight) - Caterham, Surrey 16-May-2011

Brown Hairstreak larva (36 days old - in shadow) - Caterham, Surrey 16-May-2011

Whilst these go some way towards demonstrating the point, they still do not fully capture the effectiveness of their camouflage.

After 45 days the larvae were beginning to get larger than the remaining leaves on my young plants.

Brown Hairstreak larva (45 days old) - Caterham, Surrey 26-May-2011

Brown Hairstreak larva (45 days old) - Caterham, Surrey 26-May-2011

On day 48 one larva went missing, but this time I knew it could not have got out of the netting, so it must have gone down into the leaf litter I had placed at the base of the plant. On day 49 I found it nestled under a dry leaf, but it had completely changed colour to a mottled purple. I had expected to see some subtle colour changes indicating that it was about to leave the plant, but this was not the case. One moment it was green and hanging under a leaf and the next it was gone. The other two larvae stopped feeding and descended into the leaf litter on their 54th and 58th days respectively.

After fully monitoring all three larvae at this stage of their development I was able to establish the timing and sequence of events that lead to pupation.

To begin with, apart from the size and age of the individual larva, there is very little initial indication that it is going to leave the food plant and look for a pupation site. My three larvae pupated 54 to 65 days after hatching from the egg. A fully grown larva is typically 20mm in length and lime green in colour. It is still green when it descends to the ground, showing just a few dark flecks under the skin. Around 6 hours later it has achieved a transitional colour, halfway between green and purple. Once at this point the mottled purple colouration fully asserts itself within a period of just a few hours. Thereafter it rests under a dry leaf (or other sheltered pupation site) and does not feed again.

Brown Hairstreak larva (56 days old and fully grown) - Caterham, Surrey 4-June-2011

Brown Hairstreak larva (3 hours after descending) - Caterham, Surrey 6-June-2011

Brown Hairstreak larva (7 hours after descending) - Caterham, Surrey 6-June-2011

Brown Hairstreak larva (10 hours after descending) - Caterham, Surrey 29-May-2011

Brown Hairstreak larvae (colour comparison) - Caterham, Surrey 4-June-2011

Brown Hairstreak larva (pre-pupation at rest) - Caterham, Surrey 29-May-2011

Part 2 will follow shortly

Vince

[Neil Hulme]

Great stuff Vince - another epic! I love that pink cat at 10 hours after descent.
BWs, Neil

[Vince Massimo]

The Pupa

Updated with L4 sequence in June 2015

My understanding was that once larvae left the plant they pupated in dry leaves, clumps of vegetation or crevices in the ground, so mine were given a choice of pupation sites and materials. These largely comprised dry leaves over layers of dry and moist compost. Two larvae chose the dry leaves and the other preferred a cosy corner of the pupation pot.

Typically a larva will spin a flimsy pad of silk to which it attaches its hindquarters. It then either positions itself head-down against a vertical surface or upside down flat against a horizontal surface. Once in this position its appearance changes to a more rounded shape as it contracts. It stays like this for up to 7 days and the skin becomes increasingly transparent as it approaches pupation. Unlike the larvae of many other butterfly species which enter this stage, the shape and colour of the pupa begins to become visible through the larval skin. At the point of pupation the larval skin becomes completely transparent and is slowly sloughed off, ending up as a compact mass attached to the rear of the pupa. The fresh pupa is pink but soon darkens to its final walnut-brown colouration.

Brown Hairstreak larva (L4) 6 hours before pupation - Crawley, Sussex 28-June-2015

Brown Hairstreak larva (L4) 90mins before pupation - Crawley, Sussex 28-June-2015

Brown Hairstreak larva (L4) pupating - Crawley, Sussex 28-June-2015

Brown Hairstreak larva (L4) pupating - Crawley, Sussex 28-June-2015

Brown Hairstreak larva (L4) pupating - Crawley, Sussex 28-June-2015

Fresh Brown Hairstreak pupa (L4) - Crawley, Sussex 28-June-2015

Brown Hairstreak pupa (freshly emerged) - Caterham, Surrey 13-June-2011

Brown Hairstreak pupa (5 hours old) - Caterham, Surrey 3-June-2011

Brown Hairstreak pupa (typical side view) - Caterham, Surrey 15-June-2011

Brown Hairstreak pupa (typical top view) - Caterham, Surrey 2-July-2011

The first hatching occurred on the morning of 5th July 2011. This was L2 which spent 32 days as a pupa and emerged as a male. At about 4 days prior to emergence the pupa started to darken in the area around the wings and this gradually spread to the whole pupal case, which became completely black.

Brown Hairstreak pupa (20 days before emergence) - Caterham, Surrey 15-June-2011

Brown Hairstreak pupa (male - 4 days before emergence) - Caterham, Surrey 1-July-2011

Brown Hairstreak pupa (male - 3 days before emergence) - Caterham, Surrey 2-July-2011

Brown Hairstreak pupa (male - 1 day before emergence) - Caterham, Surrey 4-July-2011

Brown Hairstreak male (reared and released) - Crawley, Sussex 5-July-2011

The adult was released back to its site of origin within a few hours. It stayed around for over an hour, occasionally taking sips of the sugar solution I had sprayed onto the leaves of the plant.

I had speculated that, based upon the relative broadness of the abdominal areas of the two remaining pupae, L1 and L3 would both be female. L3 was always a very dark pupa and gave few clues as it neared emergence. However as L1 started to darken, the wing case area began to show signs of dark orange colouration. Both emerged as females within a few minutes of each other on the morning of 13th July 2011.

Brown Hairstreak pupa (11 days before emergence) - Caterham, Surrey 2-July-2011

Brown Hairstreak pupa (female - 3 days before emergence) - Caterham, Surrey 10-July-2011

Brown Hairstreak pupa (female - 1 day before emergence) - Caterham, Surrey 12-July-2011

Brown Hairstreak female (freshly emerged) - Caterham, Surrey 13-July-2011

Brown Hairstreak female (reared and released) - Crawley, Sussex 13-July-2011

Their pupal stages lasted 30 and 32 days respectively and followed on from the 32 day development of the male (L2). As these were all reared under cover and protected from the worst of the weather, it is not clear how these conditions affected the speed of development or behaviour of the larvae. Nevertheless, these early emergences were anticipated because the eggs hatched 2-3 weeks earlier than expected. Eggs being monitored in the wild in Sussex also hatched early in 2011 and the first sighting of an adult in the wild in that year was a male in Bernwood Forest, Buckinghamshire on 11th July. This compares with national first-sighting dates of 24th July in 2010, 20th July in 2009 and 13th July in 2008.

Summary:

L1 (Female)
Hatched from egg 9th April 2011
Went missing from the food plant for two and a half days on 4th May, but relocated
Descended and stopped feeding 6th June 2011 (day 58)
Pupated 13th June 2011 (day 65) after 7-day interval
Emerged as adult 13th July 2011 (day 95) after 30-day interval

L2 (Male)
Hatched from egg 10th April 2011
Descended and stopped feeding 28th May 2011 (day 48)
Pupated 3rd June 2011 (day 54) after 6-day interval
Emerged as adult 5th July 2011 (day 86) after 32-day interval

L3 (Female)
Hatched from egg 11th April 2011
Appeared as 2nd instar 23rd April 2011 (day 12)
Moulted into 3rd instar 29th April 2011 (day 18)
Descended and stopped feeding 4th June 2011 (day 54)
Pupated 11th June 2011 (day 61) after 7-day interval
Emerged as adult 13th July 2011 (day 93) after 32-day interval

All three adults were returned to their original sites for release.

I would like to acknowledge the advice and encouragement received
from Susie Milbank during the course of this project .

Reading References:

The Butterflies of Britain and Ireland (Thomas and Lewington 2014)
UK Butterflies Website

Vince

[David M]

Utterly outstanding, Vince. Thanks for sharing.

[essexbuzzard]

Seconded! Great stuff,a truely fascinating report.

[Pete Eeles]

Superb observations Vince, as ever And saving a few lives to boot. Awesome.

Cheers,

- Pete

[Mark Colvin]

Hi Vince,

Another super report. Your dedication and observational skills never fail to impress

Brilliant ...

Kind regards. Mark

[Vince Massimo]

Many thanks for your comments everybody . I now realise that I should have done this earlier. I also realise that I did not get to see this species this year (I really need to get out more), so will soon be making an effort to survey some more tetrads in Sussex for eggs in the coming months.

Cheers,

Vince

[Vince Massimo]

Just to let everyone know that the report has been updated with 8 new images and some revised text. Basically, I have been rearing some more rescued larvae and have taken the opportunity of adding two new egg images and a rarely-observed pupation sequence of 6 images. All new images are identified with a 2015 date and L4 designation. Any new text is shown in bold.

Pete - I will speak with you about the best way of getting these revisions added to the Dispar article. I am also working on updates for two other species

Vince

[Nick Broomer]

Well done Vince, excellent observations and photos as usual.

All the best, Nick.

[Vince Massimo]

Thanks Nick
It was interesting to review this species and be able to add a new sequence.

Vince

[Vince Massimo]

This new addition to the report concerns the eggs and a phenomenon which has puzzled me for some time - namely, why some eggs look like parts of their outer shell has been worn away. The eggshell is very tough which enables the eggs to get through the winter, but it seems that the sculptured top layer may be more delicate.

Undamaged Brown Hairstreak eggs - Crawley, Sussex 2-Oct-2018

Occasionally I have been finding eggs which I assumed had been damaged by vegetation rubbing against them.

Brown Hairstreak egg - Crawley, Sussex 23-Nov-2023

But some of these had been well tucked-away, so presumably would have been protected from this sort of damage

Brown Hairstreak egg - Crawley, Sussex 23-Nov-2023

And then there was the situation where only one of a pair of eggs was damaged.

Brown Hairstreak eggs - Crawley, Sussex 28-Dec-2018

However, the loss of all or part of the outer layer does not appear to prevent the eggs from hatching.

Brown Hairstreak eggs - Crawley, Sussex 8-March-2022

Hatched Brown Hairstreak eggs - Crawley, Sussex 26-April-2022

Note that not all eggs with holes in are hatched ones. If the hole is jagged, then it is more likely due to parasitism (particularly if it happens outside of the normal hatching period of April).

Parasitised Brown Hairstreak egg - Crawley, Sussex 22-Nov-2018

In the last week I have been finding some more clues as to the possible cause of the damage. Firstly, what looked like some small pits in the side of an egg, in addition to more extensive damage at the top.

Brown Hairstreak egg - Crawley, Sussex 23-Nov-2023

Brown Hairstreak egg - Crawley, Sussex 23-Nov-2023

And then, on another egg, a minute slug-like creature, which may have been the cause, or may have just been passing through. Unfortunately I only discovered the mystery creature when I was processing the images, so was not able to observe it or its' behaviour in detail.

Brown Hairstreak egg - Crawley, Sussex 23-Nov-2023

This is all I have at the moment, so if anyone has any other thoughts or observations, they would be appreciated.

Vince

[bugboy]

I too have noticed this wear and tear during my winter egg hunts at Bookham over the years. Like you, I've presumed its due to rubbing from surrounding foliage. Presumably this outer shell needs to be more delicate or it would prevent the larvae from hatching, it might be so fragile that a passing slug could detach it simply by moving over it. I've wondered whether the lattice might be there to encourage algal growth to help camouflage the egg through the winter, I've noticed this on Purple Hairstreak eggs too. All speculation of course.

[Vince Massimo]

Thanks for your input, Paul. I will keep monitoring my eggs to look for any further changes.

Vince

[Jack Harrison]

Parasitised Brown Hairstreak egg - Crawley, Sussex 22-Nov-2028

With that date, I'm sure it must have been attacked by Mr.Enistein.

Jack

[Vince Massimo]

Thanks Jack, now corrected.

Vince