The Brimstone Project

3rd August (stones added to keep squirrels out)

18th August - growth has slowed as the process of lignification takes place. The shoot must become woody to survive the winter and keep pests at bay.

Continued growth and transformation from green shoot to woody branch.

15th July. This year's growth appears complete.

11th August - the terminal bud has grown out and flower buds quickly appear.

18th August - In full flower.

18th August - showing the full extent of Lammas growth.

Lammas Growth 2 - Once the shoot was established, one of the leading branches began to grow and then flower.

15th July, this years growth complete with dormant terminal bud.

15th July, a shoot has appeared from the base of the tree.

23rd July, the shoot measures 12cm.

28th July, the shoot measures more than 20cm in height.

Lammas Growth 1 - By mid July this tree had stopped growing. From mid-July a shoot emerged and is documented over the next few weeks.

This potted tree is watered regularly. None of the trees planted out and fending for themselves have experienced Lammas growth.

This is the first year the new trees have flowered and produced berries. This was the last berry remaining on 17th August and contained two seeds.

Frangula alnus, Alder Buckthorn seeds. One berry contained two seeds.

This was not the kind of flight usually observed in springtime where a male Brimstone flutters purposefully past and away off into the distance. This was a wide circling, sometimes low down and then high up in the trees, sometimes threading a tight weedy path, occasionally tumbling briefly with a White. Then several minutes after taking flight it appeared to settle in the tangle of burdock, nettle and bindweed shown. There one or two leaves in this image that look remarkably like Brimstone wings. Either they are (most likely not) or this serves to illustrate how easily a Brimstone could camouflage here in this scrub.

Sunday 24th August, sunny, a bright green male Common Brimstone, disturbed, flying near to the young Alder Buckthorn trees.

This berry had a bite taken out of it a couple of weeks ago. Berry was not materially damaged. Annoyingly I did not photograph the earlier damage.

Not sure if this is still ripening. It looks a bit shrivelled?

Frangula Alnus Berry. Ready for a Blackbird?

Frangula Alnus berries ripening on the same plant, photographed 27th July.

In my spot in Essex, in something of a frost pocket, male Meadow Browns must of hatched in the past week. Just a couple evident on 15th June but many on the 22nd. Well behind Blythe Valley Park it seems.

That could be a Cleopatra Butterfly (Gonepteryx cleopatra) The leading edge of the forewing (costa) is barely convex and there looks to be a yellowing inside the wing.

Alder Buckthorn (Frangula Alnus) berries forming. These saplings were planted as seedlings in March 2024. In their first year they did not flower. In their second year they successfully flowered and are now forming berries. 22nd June.

One of the two last caterpillars observed. This one started feeding again just minutes after being disturbed. This Alder Buckthorn is still flowering. 15th June.

Their charmed lives. I have been following a dozen or so (wild) caterpillars on young Alder Buckthorn planted next to a remote stream and overgrown with Common Comfrey, Nettle, Black Horehound and Water Figwort. I have not found a single chrysalis. Either I cannot find them or they were predated.

Thanks for posting these. Did they pupate on the same plant on which they were feeding? In this picture it looks as though there is an almost completely eaten leaf nearby.

Spiracles through which the larvae breathes. There are 9 down each side of the body, 1 thoracic and 8 abdominal.

Midabdominal prolegs in action.

Searching for chrysalises I disturbed the last two visible Brimstone butterfly caterpillars. Both on the same Alder Buckthorn plant and both found in this en garde posture. 15th June.

A first attempt to show the Brimstone caterpillar feeding on Alder Buckthorn. A Video might be better. Feeding is frenetic, chomp, chomp, chomp, eating the leaf in a curved action. Repeated over and over along the leaf margin.

Then resting along the midrib. Still and safe.

"Hieracium pilosella grows in dense mats, excluding other vegetation."

"If the soil in which mouse-ear hawkweed is growing is infertile, then a dense advancing front of plants will radiate from a bare center."

Hieracium pilosella = Pilosella officinarum

explorer.natureserve.org/Taxon/ELEMEN...

Two days later I find that the rapidly decayed remains are being scavenged. A Blow Fly and a pair of Scorpionflies (Panorpa). A parasite would have kept its host alive.

In retrospect I wish I had investigated further two days ago. What is all that detritus covering leaf and corpse?

A grim find. A dead or paralysed Brimstone caterpillar laying on an uneaten leaf. Its not obvious how it met its end. I thought it might have been parasitised but I am sure now that is not the case.

Evidence of a Brimstone butterfly larvae's final moult (ecdysis) from 4th to 5th instar. Anchored at the leaf base the caterpillar exits the old cuticle in a forward direction. Then off to find a clean new leaf?

Something else happened here. Is that the remains of a Damsel Bug?

This might be one a reason for Brimstone butterflies not to choose larger Buckthorn trees as larval hosts. Warblers such as this Garden Warbler seen singing in Alder Buckthorn (Frangula alnus) are known to eat Brimstone butterfly caterpillars.

Brimstone might be choosy about their choice of larval host. There may be something about that row of Buckthorn that they are avoiding.

Have you found Brimstones there on previous occasions? I have been wondering how they locate their larval host. They found my newly planted Alder Buckthorn saplings both last year and this.

4th instar common brimstone butterfly larvae. Note the amber fluid exuded from tips of fine hairs along the body. The fluid is thought to be a defense mechanism possibly discouraging predators with a foul taste.

3rd instar brimstones 31st May 2025

Fairly certain these are 2nd instar resting on the top of the leaf. A useful resource for identifying instars at www.ukbutterflies.co.uk/species.php?...

3rd instar common brimstone. 8 or 9mm long. Resting along midrib of the upperside of the alder buckthorn leaf.

2nd or 3rd instar common brimstone butterflies resting between meals. About 6mm long suggests 2nd instar. According to Peter Eeles in his book Life Cycles of British & Irish Butterflies 2nd instar catapillars would rest on the underside of the leaf. 3rd instar rest on the upper side of the leaf.

Two second or third instar common brimstones on Frangela alnus. 25th May 2025.

Alder Buckthorn (Frangula alnus) flowers. Each about 3 or 4mm across. Flowers beginning to open in late May.

Brimstone eggs.