Red Admiral (Early Stages)

Transcription

1 01 February 2014 Vince Massimo Citation: Massimo, V. (2014). Red Admiral (Early Stages) [Online]. Available from [Accessed February 1, 2014]. Red Admiral (Early Stages) Vince Massimo This article contains the results of one of my "early-stages" projects, where I photo-document the development of a target species from egg to adult and hopefully make some observations along the way. A total of 5 individuals were involved during the two months it took me to produce the final sequence of images. Many photos were taken in the wild, but others could only be obtained under controlled conditions. Red Admiral eggs are laid singly on the upperside of the leaf of the host plant, usually Common Nettle. Red Admiral ovum Woldingham, Surrey 11-July-11 After the egg hatches, the larva soon forms a small tent by folding the edges of a leaf together and binding the sides of the join with silk. These early shelters are unmistakable because they are 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. Red Admiral second-instar larval tent #1 Chaldon, Surrey 30-July-11 I watched a second-instar larva construct its second larval tent from scratch. I am not aware that this process has previously been described in detail. It first lays strands of silk across the top rear edge of the chosen leaf and then chews through the main ribs at the base of the leaf, just forward of the stalk. The silk strands stop the now weakened leaf from distorting downwards and the two upper edges of the leaf are then folded upwards and knitted together with silk, leaving a small opening at the tip. 1 of 6

2 Red Admiral second-instar larva constructing tent #2 Chaldon, Surrey 30-July-11 Red Admiral second-instar larval tent #2 Chaldon, Surrey 1-August-11 The above photo is also interesting in that it shows an earlier abandoned effort on the leaf below. It laid down the 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 (or a very small Cornish pastie). The larva emerges 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 will therefore be a succession of shelters, with the larva hopefully being found in the largest, if it survives predation. Multiple larval tents Woldingham, Surrey 1-June-12 The final tent is another very distinctive structure, 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. 2 of 6

3 Typical Red Admiral late-instar larval tent Chaldon, Surrey 22-August-11 Red Admiral larvae have several colour forms, ranging from black through greenish-brown to a very pale yellowish-green. Red Admiral final-instar larva Caterham, Surrey 23-June-11 Red Admiral final-instar larva Caterham, Surrey 23-June-11 Pupation follows a recognised sequence, commencing with the larva suspending itself upside down from the underside of a leaf or stalk. Red Admiral larva preparing for pupation Red Admiral larva just prior to commencement of pupation Red Admiral larva commencing pupation 3 of 6

4 Red Admiral larva completing pupation Fresh Red Admiral pupa Typical Red Admiral pupa Caterham, Surrey 4-July-11 The pupal stage lasted 17 days. In the days prior to hatching there were some very subtle colour changes to the pupal case, which went un-noticed until suddenly, on the final morning, the whole pupa darkened and the colours of the wings showed strongly through the outer case. Red Admiral pupa (3 minutes before hatching) Caterham, Surrey 16-July-11 Two adults were hatched and released. Both were female, one being ab.bialbata, which displayed white spots within the red bands of the forewings. Red Admiral female ab.bialbata (freshly emerged) Caterham, Surrey 20-July-11 Red Admiral female (freshly emerged) Caterham, Surrey 20-July-11 Red Admiral female (freshly emerged) Caterham, Surrey 20-July-11 4 of 6

5 2012 turned out to be a very good year for Red Admiral and the season started very promisingly when I discovered a very early egg-laying female a few hundred metres from home on 20th March. She was responsible for at least 14 eggs (3 of which were on the same nettle leaf). 3 Red Admiral ova Caterham, Surrey 20-March-2012 Many larval tents could be found throughout the season, including this one which seems to show how the larva progressed across the plant. Red Admiral larval tents Woldingham, Surrey 1-June-2012 The tent on the bottom right appears to be the first, with the larva then constructing the second on the bottom left, before progressing to the top left where the first multi-leaved shelter was formed. All tents were vacant, apart from old droppings. On 20th June I discovered a fully grown Red Admiral larva completely in the open on a nettle plant. This was taken home for further study. It fed for three days and then formed a pupation tent. 5 of 6

6 Red Admiral pupation tent Caterham, Surrey 23-June-2012 Pupation took place on 27th June and the adult emerged 12 days later on 9th July. Red Admiral (reared and released) Caterham, Surrey 9-July-2012 UK Butterflies member Nick Broomer ("hideandseek") describes in his personal diary how he monitored a larva in his garden in June Development times turned out to be slightly longer for the wild individual compared to those which were reared by me, but this is not unexpected. Summary Time spent by larva suspended before pupation: 2011 (reared) - 2 days 2012 (reared) - 2 days 2012 (wild) - 5 days Time spent as a pupa, before hatching: 2011 (reared) - 17 days 2012 (reared) - 12 days 2012 (wild) - 18 days The season ended spectacularly with reports from Neil Hulme and Mark Colvin of Red Admirals found feeding on the juices of fallen plums at a fruit farm in Ticehurst, East Sussex in mid-september. In 2011 egg-laying was recorded by Richard Roebuck at Goring, East Sussex as late as 15th November and in most years some larvae have been found to be able to over-winter in sheltered spots near the Sussex coast. Adults do not hibernate in the strictest sense, but are also able to over-winter and their numbers are supplemented by immigrants which arrive from across the Channel in Spring. 6 of 6