Monday, 22 August 2016

Brown Hairstreak, life cycle

A typical habitat for the Brown Hairstreak, large Ash trees surrounded by Oak and below, lots of the larval food plant, Blackthorn.

Large Ash tree in the middle of photo, with lots of Blackthorn along the bottom of the trees. There are 13 large Ash trees
around this meadow and the Blackthorn is growing along most of it.

Brown Hairstreaks live in the canopy of large Ash trees and feed on honeydew provided by Aphids. The females descend to lay their eggs on Blackthorn plants, when they can be observed low down nectering on local flora and also basking in the sun. Males sometimes fly down to feed on flowers when honeydew is in short supply.

A male Brown Hairstreak that has come down from the tree tops
to feed on the local Thistles.
The female Brown Hairstreaks start laying their ovum [eggs] about the middle of August. They are laid on the stems of Blackthorn on both mature plants and young shoots, anywhere from 150mm [6inches] to 1650mm [5.5feet] high, and in sunny sheltered positions, [so i have been lead to believe]. This behaviour was witnessed when i joined Francis Kelly and a team of enthusiasts  from the Surrey branch of B.C. doing an egg search/count earlier this year, [2016, and  each egg found was authenticated, 57 where found.

I conducted my own search for Brown Hairstreak eggs later that year [in the Autumn] in the same area, [Cranliegh Fields] when i found 210 eggs, [between September-November 2016]. The two fields that i conducted my search were divided into eight areas, Area A, B, C, D, E, F, G,H. The most productive area was Area A, where 78 eggs were found in a very well sheltered area with no sun [during the winter] with a north westerly outlook another 41 eggs in Area G, were found in a similar position with a North-westerly outlook, in a rather well sheltered situation with no sun. Area B, 12 eggs, Area C, 10 eggs,  Area D, 5 eggs and  Area E, 7eggs, [Both with very little Blackthorn] Area F, 33 eggs [lots of good Blackthorn] were in sun/shade. Area H which is in full sun, [with an excellent expanse and the most Blackthorn in one area] which i thought i would find good numbers, only produced 24 eggs. I followed this up with a further search in an adjoining field, finding a further 109 eggs. 23 eggs were found in a very well sheltered area facing south, south-west. A high majority of the other eggs were found facing north, north-west. Total egg count 319. Total search hours, 13. They overwinter at this stage.

Brown Hairstreak ovum 150mm [6 inches] off the ground.
The egg is about 2 thirds up the middle of the photo/front stem.

Two Brown Hairstreak ovum was found on this isolated Blackthorn plant, out in the open in this meadow.The
following winter 4 ovum were found on this particular plant.

A  sunny but, sheltered area of Blackthorn where eggs were laid.
The ovum [eggs] are laid singly, normally one by itself, but sometimes they can be found in small clusters of two or more, the most i have found together were a group of four, [probably laid by the same female].

Four  Brown Hairstreak ovum laid in a small cluster, which is
quite uncommon.

Two Brown Hairstreak ovum as they would commonly be found.

A freshly laid Brown Hairstreak ovum

A Brown Hairstreak ovum after a long winter and close to hatching.
Photographed, 19th April.

The tiny larva start to emerge anywhere from late April to the middle of May, and sometimes later, depending on the weather. During the day the larva rest on the underside of the Blackthorn leaves, normally feeding only at night, [but this is not 100% as i have witnessed them feeding by day]. There are three moults, [four instars]. The larval stage lasts about eight weeks.

1st instar Brown Hairstreak larva, about 1.5mm in length. Less than
24 hours after emerging from the egg, [feeding early evening]. Date 26th April.

Brown Hairstreak 1st instar larva, 8 days old and still only 2.5-3mmm in length.
This could be down to the cold weather conditions at the time, which would slow both the
larva's eating and growth rate down.

A late 2nd instar Brown Hairstreak larva, 8mm in length, 24 days old, 19th May. The green larva
is beautifully camouflaged and, will stay this colour until its close to pupating. On the 2nd of June
2 weeks later i found another 2nd instar larva, again 8mm in length. Indicating the time difference
between hatching larva.
3rd instar Brown Hairstreak larva resting on the back of a Blackthorn leaf,
10mm in length, 29 days old. The weather is a lot warmer now and, the larva
is growing at a much faster pace.

After only 10 days as a 3rd instar, the Brown Hairstreak larva has made
its final moult, length 12mm,  34 days old.

When the larva are ready to pupate, they descend the host plant to find a suitable crevice in the soil, or a leaf amongst the litter at the base of the Blackthorn to make it's final changes.

After 57 days the 4th instar Brown Hairstreak larva descended to the base of the Blackthorn
to start the final colour change of the larva before finding a suitable place to pupate.

A few hours later the Brown Hairstreak larva has changed  colour

Another hour later and the larva has changed it's appearance again, [rather like that
of a Chameleon] blending in with it's surroundings.

24 hours later, having changed colour again, it seems that the final instar Brown Hairstreak larva
 has chosen this leaf to pupate on.

But no, the larva decided to move. Not being happy with it's first choice of leaf
went on a walk-about to find something more suitable. Same larva as above 48
hours later, different leaf, and it's final chosen place to pupate.

The following day, early morning. The Brown Hairstreak larva has made it's final
colour change before pupating. Date, 25th June.

8 hours later the same day the larva has pupated. Date, 25th June.

A week before the Brown Hairstreak finally emerges.

24 hours before the butterfly emerges the pupa turns a beautiful black in colour. Just
short of one year from when the egg was first laid.

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