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brown hairstreak   <>   thecla betulae   <>   stiallach donn


  DHardiman 2002   

Habitat:  The Brown Hairstreak is quite rare in Ireland being mainly confined to limestone areas of counties Clare and Galway.  It was formerly much more widespread.  
It is single brooded.
Larval Food Plant:   Blackthorn  Prunus spinosa
Flight Time:  Late July to mid-September 
Hibernation:   Overwinters as an ova.

The upper side of the wings are dark-brown with a slightly greyish hue and a faint pale mark is visible on the upper part of each forewing  in the male. The female's upper wings are dark-brown with a broad orange band on each forewing. On both there are two orange marks on each hindwing, one on the tail and the other at the prominent anal angle.  When seen with the wings closed the golden-brown underside, which is richer in colour in the female, is crossed by two white lines.  The female is slightly larger than the male and has a longer tail.


Brown Hairstreak butterfly

  DHardiman 2002  



    Life Cycle of  the Brown Hairstreak


The tiny white bun-shaped eggs are c.0.65 mm in diameter and laid singly or in pairs in a leaf axil or among 
the buds of the food plant in late July or August. They do not hatch until the following spring. The embryo is 
partially developed before overwintering and resumes developing in spring, eventually hatching over a 
period of  10 days in late April  and early May.

  Brown Hairstreak ovum on 
  Blackthorn             DHardiman 2001


The adult larva measures up to 18 mm in length.
Its woodlouse shaped body is broad and plump  becoming flattened at the extremities and is strongly indented
between the segments.   The green body has whitish divisions between the segments and  two close pale yellow
dorsal lines that diverge towards the head.  A series of  oblique pale yellow lines extend along both sides.
The dark brown head withdraws into the body at rest.

Brown Hairstreak larva on Garlic Mustard

              DHardiman 2002

After the first instar the larva rests by day on a silken pad spun on the underside of a Prunus leaf and feeds by
 night.   Feeding takes place between late April and the end of June.   This larval stage lasts 4-6 weeks.


Pupa attaches itself  to the undersides of  leaves or among leaf  litter beneath its  food plant by a group of spines
that are present in the anal region covered over by larval skin, this taking the place of the cremasteral hooks.
The presence of a silken girdle, in addition to this, is disputed.   When the larva pupates among leaf  litter it
forms a shelter by drawing a few leaves together with silk threads. This pupal stage lasts 30-40 days.

  DHardiman 2002

The adult emerges in late July or early August and is on the wing until mid-September.   



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