Red Admiral (Early Stages)
Posted: Fri Aug 26, 2011 12:33 pm
The Red Admiral is primarily a migrant to our shores, although sightings of individuals and immature stages in the first few months of the year, especially in the south of England, mean that this butterfly is now considered resident. This resident population is considered to be only a small fraction of the population seen in the British Isles, which gets topped up every year with migrants arriving in May and June that originate in central and southern Europe. This particular species is often observed flying into a headwind on its in-bound and out-bound migrations. The butterfly is not able to hibernate in the strictest sense of the word and the majority of adults leave the UK in late August to mid-October without mating and fly south to the winter breeding grounds in southern Europe. Those that remain are usually unable to withstand our winter, especially in the cooler regions of the British Isles, however there have been increasing records of small numbers of adults overwintering during mild winters. Regular records also exist of late eggs and larvae which develop slowly in very sheltered locations, usually on or near the south coast, and produce spring adults. As will be described later, it has now been established that eggs can be laid throughout the winter and larvae can hatch in any month of the year. Because it does not hibernate, the butterfly can become active on any sufficiently warm day in winter, so can be seen in any month of the year. When surveying for overwintering butterflies during the winter of 2014/2015 I recorded and photographed a specific individual butterfly on 6th December 2014 and again, 64 days later on 8th February 2015.
The Ovum and Larva
Red Admiral eggs are laid singly on the upperside of the leaf of the host plant, usually Common Nettle (Urtica dioica). They are similar in appearance to those of the Comma, but in my experience they are laid towards the middle of the leaf, whilst the Comma tends to prefer the leaf edges. However this is not always the case and there are inevitable exceptions
After hatching, the larva initially forms a silken tent on the underdside or upperside of a tender leaf, or within the terminal leaves of the plant. As it feeds and grows the shelters become more elaborate. In November 2015 I observed a larva progressing through a series of shelters, all of which were different. This may not be typical behaviour in this case because the larva in question was the result of a late egg and its development could have been affected by the colder weather.
The variability in the colour of the larva starts in the second instar which can be either completely dark or have pale yellow markings, including some yellow-tipped spines.
The third instar is similarly dark or coloured, but all now have a noticeable broken yellow stripe low down along the side and also more complex and branching spines
By its third instar it generally proceeds to construct a full tent by folding the edges of a leaf together and binding the sides of the join with silk. The following two images show the progression of a larval tent utilised by an overwintering larva which chose to feed entirely within the structure and moulted inside the remainder. However not all shelters fit this pattern and some may be folded downwards.
These early shelters are unmistakable because they are usually very symmetrical, unlike the tents formed by some moths and other insects and spiders which also feed or shelter on nettle. The most likely cause for confusion that I have observed is a type of shelter formed by some larvae of the Small Tortoiseshell when they start to disperse from their communal webs. They construct and use these for protection during the few days when they are moulting. However these tend to be found near the old webs and there are often several in a small area. Another common cause of confusion are the tents of the Nettle-tap moth larva which are very common at the same time of year.
I watched a third-instar larva construct a larval tent from scratch. It first lays strands of silk across the top rear edge of the chosen leaf, just forward of the stalk and then chews some holes in the base of the leaf, avoiding the main veins. The silk strands may stop the now weakened leaf from distorting downwards and the two upper edges of the leaf are then gradually knitted together with more silk, leaving a small opening at the tip.
The above photo is also interesting in that it shows an earlier abandoned effort on the leaf below. The larva laid down the first silken strands but then decided to move to another leaf. The resulting structure is unlike anything else and is reminiscent of a closed Venus fly-trap leaf. The original hole(s) made by the larva at the base of the leaf should still be visible, although it is sometimes obscured by folds in the leaf. This particular feature confirms that the shelter was made by a Red Admiral larva.
The larva emerges from its shelter to feed on adjacent leaves, but also partly consumes its early shelters and constructs larger ones as it grows, usually higher up the same plant. There should therefore be a succession of shelters, with the larva hopefully being found in the largest, if it survives predation. Succeeding shelters will not necessarily be of the folded leaf type and the larva may move to other plants.
Some final tents can be very distinctive structures, usually formed at the top of the plant and comprising a number of leaves knitted together with silk. Part of the process is that the larva chews part-way through the top part of the main stem, which topples but remains attached to the plant. The larva continues to feed in this shelter and may pupate inside if there is sufficient room. If not, it utilises larger leaves further down the plant, which are loosely joined together with silk strands.
It has been observed that pupation tents can usually be distinguished from ordinary shelters by having additional supporting external silk strands.
Red Admiral larvae have several colour forms, ranging from black through greenish-brown to a very pale yellowish-green. These colours mainly appear in the final instar and usually intensify and change significantly as the larva becomes full grown.
The Pupa
Pupation follows a recognised sequence, commencing with the larva suspending itself upside down from the underside of a leaf or stalk.
In the above case, the pupal stage lasted 17 days. In the days prior to emergence there were some very subtle colour changes to the pupal case, until suddenly, on the final morning, the whole pupa darkened and the colours of the wings showed strongly through the outer case.
In 2011 two adults were reared and released. Both were female, one being ab.bialbata, which displayed white spots within the red bands of the forewings.
Large and small larval tents are easy to spot, so it is worth checking out your local nettle patch, especially on fresh growth in a sunny, sheltered location.
Vince
Reading References:
The Butterflies of Britain and Ireland (Thomas and Lewington 2014)
UK Butterflies Website
The Ovum and Larva
Red Admiral eggs are laid singly on the upperside of the leaf of the host plant, usually Common Nettle (Urtica dioica). They are similar in appearance to those of the Comma, but in my experience they are laid towards the middle of the leaf, whilst the Comma tends to prefer the leaf edges. However this is not always the case and there are inevitable exceptions
After hatching, the larva initially forms a silken tent on the underdside or upperside of a tender leaf, or within the terminal leaves of the plant. As it feeds and grows the shelters become more elaborate. In November 2015 I observed a larva progressing through a series of shelters, all of which were different. This may not be typical behaviour in this case because the larva in question was the result of a late egg and its development could have been affected by the colder weather.
The variability in the colour of the larva starts in the second instar which can be either completely dark or have pale yellow markings, including some yellow-tipped spines.
The third instar is similarly dark or coloured, but all now have a noticeable broken yellow stripe low down along the side and also more complex and branching spines
By its third instar it generally proceeds to construct a full tent by folding the edges of a leaf together and binding the sides of the join with silk. The following two images show the progression of a larval tent utilised by an overwintering larva which chose to feed entirely within the structure and moulted inside the remainder. However not all shelters fit this pattern and some may be folded downwards.
These early shelters are unmistakable because they are usually very symmetrical, unlike the tents formed by some moths and other insects and spiders which also feed or shelter on nettle. The most likely cause for confusion that I have observed is a type of shelter formed by some larvae of the Small Tortoiseshell when they start to disperse from their communal webs. They construct and use these for protection during the few days when they are moulting. However these tend to be found near the old webs and there are often several in a small area. Another common cause of confusion are the tents of the Nettle-tap moth larva which are very common at the same time of year.
I watched a third-instar larva construct a larval tent from scratch. It first lays strands of silk across the top rear edge of the chosen leaf, just forward of the stalk and then chews some holes in the base of the leaf, avoiding the main veins. The silk strands may stop the now weakened leaf from distorting downwards and the two upper edges of the leaf are then gradually knitted together with more silk, leaving a small opening at the tip.
The above photo is also interesting in that it shows an earlier abandoned effort on the leaf below. The larva laid down the first silken strands but then decided to move to another leaf. The resulting structure is unlike anything else and is reminiscent of a closed Venus fly-trap leaf. The original hole(s) made by the larva at the base of the leaf should still be visible, although it is sometimes obscured by folds in the leaf. This particular feature confirms that the shelter was made by a Red Admiral larva.
The larva emerges from its shelter to feed on adjacent leaves, but also partly consumes its early shelters and constructs larger ones as it grows, usually higher up the same plant. There should therefore be a succession of shelters, with the larva hopefully being found in the largest, if it survives predation. Succeeding shelters will not necessarily be of the folded leaf type and the larva may move to other plants.
Some final tents can be very distinctive structures, usually formed at the top of the plant and comprising a number of leaves knitted together with silk. Part of the process is that the larva chews part-way through the top part of the main stem, which topples but remains attached to the plant. The larva continues to feed in this shelter and may pupate inside if there is sufficient room. If not, it utilises larger leaves further down the plant, which are loosely joined together with silk strands.
It has been observed that pupation tents can usually be distinguished from ordinary shelters by having additional supporting external silk strands.
Red Admiral larvae have several colour forms, ranging from black through greenish-brown to a very pale yellowish-green. These colours mainly appear in the final instar and usually intensify and change significantly as the larva becomes full grown.
The Pupa
Pupation follows a recognised sequence, commencing with the larva suspending itself upside down from the underside of a leaf or stalk.
In the above case, the pupal stage lasted 17 days. In the days prior to emergence there were some very subtle colour changes to the pupal case, until suddenly, on the final morning, the whole pupa darkened and the colours of the wings showed strongly through the outer case.
In 2011 two adults were reared and released. Both were female, one being ab.bialbata, which displayed white spots within the red bands of the forewings.
Large and small larval tents are easy to spot, so it is worth checking out your local nettle patch, especially on fresh growth in a sunny, sheltered location.
Vince
Reading References:
The Butterflies of Britain and Ireland (Thomas and Lewington 2014)
UK Butterflies Website