Friday, 22 December 2017

Masters of Disguise

Butterflies and moths are near the bottom of the food chain and they have many predators. Different species adopt numerous strategies to protect themselves from being eaten. Some species are extremely distasteful to predators and advertise the fact by displaying warning colours that are generally recognised by predators. Other species use startle tactics, suddenly displaying eyespots and other markings designed to confuse a predator long enough for the target to make its escape.
Butterflies and moths are probably most vulnerable when they are at rest or during their immature stages and in the vast majority of cases, cryptic markings are used to make them blend into the background. Again, different strategies are adopted, ranging from straight-forward camouflage markings to mimicking broken twigs or bird droppings. 
Nearly all butterflies roost with their wings closed and it is usually their underwings that are cryptically marked. On the other hand, moths nearly always roost with wings spread and the upperside of their wings are often unobtrusively marked.
The Grayling (Hipparchia semele)
This butterfly virtually disappears into the background when at rest. If it feels threatened it will usually flash its eyespots before then taking off. The first photograph shows a female and the next two are of a male.

The Chinese Character (Cilix glaucata)
This species of moth is a classic bird dropping mimic.

The following photographs are of several Geometrid moths that are among many species that use their markings to blend into the background.
Red-green Carpet (Chloroclysta siterata)

Green Pug (Pasiphila rectangulata)

Double-striped Pug (Gymnoscelis rufifasciata)

Pale Brindled Beauty (Phigalia pilosaria)

Waved Umber (Menophra abruptaria)

Engrailed (Ectropis bistortata)

Grey Birch (Aethalura punctulata)

Even larger species such as the hawkmoths can be easily overlooked from just a short distance away.
Lime Hawkmoth (Mimas tiliae)

Eyed Hawkmoth (Smerinthus ocellata)
The diagonal body stripes make sense when you see the larva resting on the foodplant.

Lobster Moth (Stauropus fagi)

Buff-tip (Phalera bucephala)
This species is a broken twig mimic and bears an uncanny resemblance to a piece of birch.

Pale Prominent (Pterostoma palpina)
Another stick mimic.

Pale Pinion (Lithophane hepatica)
A stick or bud mimic.

Merveille du Jour (Dichonia aprilina)

Red Underwing (Catocala nupta)


Saturday, 25 November 2017

Life Cycle of the White Admiral

Now that autumn is moving towards winter, much of my time will be spent working in the wood. Rhododendron and bracken control is always on the agenda but coppicing, ride widening and wood thinning are essential in order to maximise potential breeding habitat for butterflies and moths.
Historically, most of our (now rare) woodland fritillary species would have been common in our wood. However, species such as the Pearl-bordered (Boloria euphrosyne), Small Pearl-bordered (Boloria selene) and Heath (Melitaea athalia) Fritillaries are highly unlikely to return naturally. I therefore focus my efforts on keeping the habitat right for species like the White Admiral (Limenitis camilla), which breeds in the wood in small numbers and also to encourage the Silver-washed Fritillary (Argynnis paphia) to increase its tiny population.
Life Cycle of the White Admiral (Limenitis camilla)
During the winter months, the White Admiral (L.camilla) hibernates as a tiny larva. It emerges from its hibernaculum in early spring and is fully grown by the end of May or early June. The pupa stage lasts for 2-3 weeks and the adult butterflies are usually on the wing from mid-June until the end of August. The ova are laid on honeysuckle leaves and the next generation of young larvae will start to build a new hibernaculum for the coming winter. 
A third instar larva remains close to its hibernaculum and a recently shed skin can be seen just above and behind the larva. (20th April 2015)

A fourth instar larva on honeysuckle. (28th April 2017)

A fifth instar larva on a honeysuckle stem. (21st May 2017)

The same larva is suspended from a stem node of honeysuckle about 15 feet from the ground and in 90% shade. (27th May 2017)

Two hours later and the larva has shed its final skin. The pupal membrane is yet to harden.
 (27th May 2017)

The same pupa (dark form).  (29th May 2017)

The same pupa (dark form). The pupa in this species has evolved to look like a crumpled honeysuckle leaf. The shadowy markings and reflective mirrors are clearly designed to break up its outline and make it less visible to predators. (4th June 2017)

Another final instar larva prepares to pupate beneath a honeysuckle leaf about 7 feet from the ground.
(31st May 2017)

The next day, the same larva has pupated. (1st June 2017)

The same pupa has adopted the more usual colour form. (2nd June 2017)

The same pupa. (4th June 2017)

The same pupa. (9th June 2017)

Sadly, the same pupa has been predated upon by a bird. Only the cremaster remains attached to the underside of the leaf. (11th June 2017)
The following three photographs are of a male White Admiral, freshly emerged from the dark form pupa. The left antenna is missing its tip and its left foreleg appears to be paralysed. After it had hardened its wings, I watched it fly up into the woodland canopy. (14th June 2017) 

The recovered pupa case shows that the pupa has sustained an injury or damage during its development. This has clearly interfered with the formation of the left antenna and is probably the cause of the paralysis in the left foreleg. (15th June 2017) 
My camera is not ideal for taking photographs of a pin-head sized ovum in subdued light but this image shows that the ovum is typically laid on the upper edge of a honeysuckle leaf.
(8th August 2017) 
The following photographs are of a second instar larva constructing its hibernaculum in preparation for the coming winter. The larva was about 6mm in length. (8th August 2017)

Tuesday, 7 November 2017

Battle for Survival

Soon, the focus of my attention will turn to scanning the horizon for raptors that overwinter across Pevensey Levels. However, while insects are still about, my gaze was firmly fixed on the field edges and hedgerows on Sunday, as Carol and I wandered around our usual circuit. Even into November, Common Darter (Sympetrum striolatum) were still numerous and a female Red Admiral (Vanessa atalanta) was busy laying eggs on nettle plants.
As we neared the end of our walk, I noticed a mini-drama taking place on the trunk of an oak tree, about 3 feet from the ground. A battle for survival was unfolding as we watched a Devil's Coach-horse Beetle (Ocypus olens) trying to subdue and dismember its prey; a species of Ground Beetle. The predator has to feed to survive and the prey species was desperately trying to escape its grasp. We watched for several minutes as the prey dragged the predator with it as it tried to release itself. The predator tenaciously hung on as it used its jaws rather like a tin-opener to cut through the wing case (elytron). The prey beetle seemed doomed but as the struggle continued, they both lost their footing and fell to the ground and were separated on impact. Battle was not rejoined and they went their separate ways. 
Devil's Coach-horse Beetle (Ocypus olens) (with prey)

 Just over a week ago, when I last put out the moth-trap, the catch was very small but did include two specimens of the scarce migrant moth Palpita vitrealis. This species has been arriving in southern England in good numbers in 2017.
Palpita vitrealis

Beaded Chestnut (Agrochola lychnidis)

Vapourer Moth (Orgyia antiqua) (male)