New tortoiseshell butterflies

Posted: Friday 20 June 2014
by Kate Bradbury

The caterpillars I rescued from a nettle patch sprayed with weedkiller have turned out to be small tortoiseshells.

Tortoiseshell butterfly

I never manage to see butterflies emerging from their chrysalides. Last year I raised six small tortoiseshell caterpillars taken from nettles, and missed the emergence of the butterflies by minutes – they chose to do so in one fell swoop at 8am one Saturday.

I had high hopes for seeing some of my recent rescue butterflies break out from their chrysalides. The batch of caterpillars I collected two weeks ago all developed well. Except that the final instar three, which pupated within a day of me taking them from the sprayed nettles, are still ensconced. Their chrysalides are black and cracked; and despite seeing them wriggle inside occasionally I now wonder if they will ever emerge.

By comparison, the others are turbo butterflies. These are the 44 or so early instar caterpillars I mentioned in my recent blog post, which all turned out to be small tortoiseshells. These ate nettles every day with gusto, and eventually pupated last week. I arranged many of the pre-pupating caterpillars on sticks, which, as butterflies, they would be able to clamber on to in order to dry their wings safely. Some seemed happy on the walls of the ice cream tub, so I just left them there.

They have been in their chrysalides barely a week, and yet four of them popped out yesterday. As I write, another chrysalis is wriggling gently, but I’ve been fooled by this behaviour before – it may just turn black and never release the butterfly inside.

I don’t know what governs the timings of butterfly development in a chrysalis (temperature, humidity?), but I wonder if the caterpillar’s diet has anything to do with it. Until I found them a new home, the three final instar caterpillars had, for at least a couple of days, been eating nettles sprayed with weedkiller. The 44 early instar caterpillars were so tiny they would have eaten fewer sprayed nettles, and have instead been feasting on a steady supply of luscious nettle tips selected and hand-picked by yours truly.

Regardless of how long it takes, it’s wonderful seeing so many small tortoiseshell butterflies. This species has declined dramatically in recent years, and before last summer I’d barely seen any in the last decade. But the hot, sunny weather of 2013 helped boost numbers, and this year is proving to be a bumper one for small tortoiseshells. As well as the 44 chrysalides in my bedroom, I’ve spotted another two batches of caterpillars in the local park, and heard reports of many happy caterpillars from Twitter and Facebook contacts.

I just wish councils and allotment societies were more aware of the plight of these butterflies – I’m dreading visiting the park one day to find the nettles have been sprayed or cut down. If the council can leave them alone for one more week, the caterpillars may yet become butterflies.

For more information on the plight of the small tortoiseshell and how you can help, don’t miss the July 2014 issue of Gardeners’ World Magazine, in shops from Thursday 26 June.

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Talkback: New tortoiseshell butterflies
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RAGDOLL520 20/06/2014 at 14:02

How lucky you are to have butterflies, I have 2 buddliea trees in full flower and not a butterfly to be seen I haven't seen any at all in my garden for months. Last year I had hundreds on my buddliea this year none. I have had only 1 bee on them as well. Does anyone know whats happened to them? Even my friends as far as Fleetwood have had none at all. I am so disappointed.

Kate Bradbury 20/06/2014 at 15:32

Edd - I think there are a couple of native moths which have adapted to feed from buddleia; the mullein moth and gothic to name two.

Raddoll520 - it's not quite garden butterfly season yet, July and August are the key moths. if you cut your buddleia down in May it should flower in time for their late-summer emergence. But Edd's right, if you would like to see more butterflies, the best thing to do is grow nettles, which their caterpillars eat.

Kate Bradbury 20/06/2014 at 16:27

Not the bordered gothic but the gothic...

Fairygirl 20/06/2014 at 17:00

I have just discovered a load of caterpillars hatching on my new blackthorn hedge - they're tortoiseshells or peacocks which were in the garden last year enjoying the buddleia. There wasn't much plant life in the garden a year ago but it's great to see more wildlife enjoying what I've put in during the last twelve months.

I've left a couple of nettles to grow in a corner too.

Robbie182 25/06/2014 at 11:29

Was looking forward to this update, great job Kate :^}

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