Small Tortoiseshell

[Jack Harrison]

BBC article:

http://news.bbc.co.uk/1/hi/uk/7634873.stm

Question. Does the Sturmia bella parasite really lay eggs on nettle which are then accidentally eaten by the Tortoiseshell larvae? That sounds a little unusual. Do in fact S.bella actually lay their eggs on the caterpillars which on hatching, merely burrow into their hosts?

Are Peacocks and Commas equally susceptible to this parasite? Numbers of those species have been very normal this year.

As for Small Tortoiseshell decline and recovery, in my 60+ years experience, numbers have always cycled up and down. I had always assumed that this is (as in the better documented case of the Holly Blue) merely the interaction between butterfly and parasite. When the butterfly numbers increase, then parasite numbers follow. The butterfly numbers plummet as they are killed off, but then the parasites have fewer hosts so they in turn decrease...and the cycle continues.

Jack

[Shirley Roulston]

What didn't help if anyone else noticed. When I really began to be interested in butterflies is September 2006, the flowering ivy was everywhere smothered in butterflies, Small Tortoiseshell's, Red Admiral's, Comma's, Painted Ladies, they were masses in every patch of ivy, it was a wonderful sight. Last September running into Autumn the ivy didn't flower at all, I live right in the countryside and I couldn't see one butterfly at all, so if they didn't get the nectar that they need for hibination maybe they died duing the winter. Just maybe, with the ivy at its best at the moment, it'll give the butterflies that do hibinate a good start to the long winter. Of course, we'll have to wait until next Spring to see if the numbers are up. One question, when you find a Small Tortoiseshell in the house in the winter, why is it usually dead? Shirley

[Pete Eeles]

One question, when you find a Small Tortoiseshell in the house in the winter, why is it usually dead? Shirley

Because it's dried out due to central heating, usually, or simply the fact that, outside, there is a massive amount of moisture. Even in midsummer, you still get dew on the grass in early morning. I don't think it's anything to do with lack of nectar sources.

Cheers,

- Pete

[Pete Eeles]

Question. Does the Sturmia bella parasite really lay eggs on nettle which are then accidentally eaten by the Tortoiseshell larvae? That sounds a little unusual.

I agree Jack - it is unusual. But I believe this is also correct.

Some photos of the nasty critter are here: http://tachinidae.org.uk/site/get-speci ... brcno=9301

Out of interest, of the 9 Red Admiral larvae I rescued from a local park, all pupated, and 6 emerged fine. The others resulted in a Sturmia bella larva emerging from the pupa and then pupating itself. The fly emerged 8 days later (on average). This is the first time I've every seen this, and I rescue Red Admiral larvae most years.

Cheers,

- Pete

[Jack Harrison]

Small Tortoiseshell do not do well attempting to hibernate in modern warm houses. I try to discourage them coming indoors at this time of year and "point" them towards the unheated barn/garage.

I have previously commented that I have had good success with keeping butterflies in a sealed container in the fridge over the winter. Orange Tip pupae survive very well and I have had Brimstones and Peacocks go through. I have enjoyed bringing the box with dormant a Peacock out into warmer conditions in say mid-April (I take care not to try to waken them too early). I don't of course put the box in the sun but put inside the garage in the shade on a sunny day with a spring temperature of say 13 degrees. It is lovely to see how they gradually wake up and then are ready to fly.

So I would suggest that if you do find a Tortosieshell insisting on trying to hibernate indoors in a centrally heated house, as soon as possible, remove it carefully and put inside a plastic box. Cool slowly (in the garage say) for a few days and then bring into the fridge. Certainly this would give a far better chance of survival than leaving indoors.

I am told that Tortosieshells do very well hibernating inside cold churches. I have no first hand experience of that as churches are not within my range of habitats

Jack

[eccles]

That's unwelcome news about the parasite hitting red admirals, Pete. I hope this doesn't mean a crash of this species too.
On the small tort front, the mass influx to the southern counties last month from continental Europe was encouraging news. I witnessed an example of this first hand at Puxton Moor in Somerset where there were hundreds of individuals nectaring off thistle along the banks of one of the rhines. Hopefully good numbers will overwinter successfully.

[Jack Harrison]

Is there any evidence that numbers were substantially boosted by immigrants? It certainly wasn't a good year in general for migrants. Did anyone actually witness the immigration of Small Torts? Seeing them inland in quantity is surely no proof as to their origin.

Small Tortoiseshell numbers were already climbing in the summer brood in early July. These were surely British bred individuals and the offspring of those were what we enjoyed at the end August/September.

As I have said before, in my 60+ years experience, ST numbers fluctuate enormously from year to year. Breeding from wild caterpillars has often produced a significant percentage of parasatized individuals, and that was long before Sturmia bella arrived here. And in any case, if Sturmia bella has such a devastating effect as is claimed, then surely it would have an equally devastating effect on mainland Europe and result in few "surplus" butterflies to migrate across to Britain?

I am not saying that there were no immigrants, but I merely ask for proof that was the reason for much greater numbers of Small Torts in late summer - reports of them coming in off the sea, for example.

If past experience is anything to go by, Small Torts will have a good showing after hibernation and we'll all be encouraged. But then as the parasitic interaction cycle favours the parasites, number of butterflies will again crash - maybe not next summer but surely within a year or two.

Jack

[Tony Moore]

Hi Jack,

I don't know about the South, but up here (Stafford) we had reasonable numbers of post-hibernators in the spring, but no larvae have been found and only one adult acouple of weeks ago. Sure as s***, something unusual has happened!

T.

[NickB]

Looking at my own sightings this year, I saw a few early emergees of ST's in Cambs, then just the odd one or two until about a month ago when they were the commonest butterfly I saw on my weekend cycle-rides for a couple of weeks. As Jack says, proof that they arrived from the continent seems to be anecdotal or an assumed fact to account for the large numbers which were reported across the country (but not everywhere, it would seem). Since it only takes a few females to have a large number of broods in any locality, could it not be that this is the case; we have all seen how large numbers of other species, like Peacocks, can be found in this way, why not ST's?
N
PS It was also mooted that Large Whites, which also, in my locality at least (despite Jack's efforts to re-populate the East of England by providing them with a garden full of foodplants!), were more abundant late in the season than earlier, were also migrants from the continent...

[eccles]

STs that I saw in September were numerous in south Somerset, with just a few found in north Somerset, and none at all locally in South Gloucestershire. It could be that local conditions were good for a sudden emergence of locally produced offspring, but it could also be the Azores high pressure dragging them from the continent. As for why continental populations are better able to withstand parasites than the UK, I can only suggest that the UK government's lamentable policy on wildlife corridors, i.e. non-existent, means that once a local population is hit then it cannot recover easily.

[Neil Hulme]

Sunday 12 October 2008: Many thanks to Colin Knaggs (BC Sussex) for taking part in the national Sturmia bella survey. He collected 32 Small Tortoiseshell caterpillars from his local Ferring Rife and bred them through, in order to determine the percentage attacked by this parasitoid tachinid fly. Colin left the healthy pupae in my care, as he was due to be away from home for a while. We are awaiting results of the parasitoid analysis from the University of Oxford. This left me with the joy of releasing healthy adults back onto the Rife. Once the adults had emerged from their beautiful, metallic chrysalides, I gave them a pre-hibernation feast of 'five portions' of fruit.
Neil

S.bella project pupae.jpg (221.79 KiB) Viewed 1358 times

S.bella project release2.jpg (152.02 KiB) Viewed 1358 times

[NickB]

I collected some ST larvae for someone who wanted to contribute to the Oxford study and she has sent me this report-back:

"There were about 12 of them, and 6 were parasitised by the ichneumon whose grubs look like the ones that emerge from a large white caterpillar and form a fluffy cocoon, Apanteles glomeratus. But googling quickly, Apanteles glomeratus appears to be confined to Pieridae. Owen Lewis at Oxford has a research project on Sturmia bella, and his ‘how to record’ notes suggest that the fluffy parasite is a Braconid, Cotesia vanessa. It certainly is not Sturmia bella, whose grub descends on a thread and turns into a brown ball, which hatches as a surprisingly large fly.

Determined to involve a rather superior and bored ten year old boy, I got out my mini Swiss army knife and cut one of the two cocoons in fluff balls, and found a honeycomb structure. I shall send the remaining 5 cocoons to Owen Lewis at Oxford, and hope he agrees.

Last year my Small Tort parasites were all Phobocampe confusa, I think"

So, who IS to blame for the decline?

N

[Jack Harrison]

I am confused as to the brood structure of Small Tortoiseshells. I saw new emergences on 15th June and they clearly were offspring of the hibernators. I had understood that these June individuals bred again to produce the late summer emergences (compare Comma life cycles). Yet I am still seeing huge numbers of pristine Tortoiseshells on 15th July (plus the occasional very tatty one). I cannot imagine that these are the offspring of the mid-June emergence so presumably late emerging offspring of the hibernators.

I can only surmise that the life cycle is complicated. Some develop quickly and emerge mid June. These breed and we see their offspring late August/September. Meanwhile, some (from hibernators) develop much more slowly and these are the ones we are seeing now in mid July in huge numbers that will eventually mingle with their “nieces and nephews” in late summer. But I really don’t know what happens. Any better ideas?

This individual on an interesting basking site today, garden conifer. Bet the SLR users hate the sharp backgound


Jack

[Gruditch]

This individual on an interesting basking site today, garden conifer. Bet the SLR users hate the sharp backgound

Even with a DSLR, not sure a diffused background's possibly there Jack

Small Tortoiseshell's numbers on the rise, Seen many ST's over the last few day's, even half a dozen in our garden.

One of seventeen seen at Danebury yesterday.

Gruditch