Waiting in the dark – the moth’s struggle for survival

Moths are some of my favourite creatures: so many species to see, so little time! Luckily, with my new position as Volunteer Reserve Officer at Pistford Water in Northamptonshire, I have the perfect opportunity to practise my moth ID skills. Every morning, I help Reserve Officer and moth expert Mischa check the two moth traps on the reserve: one of the most stunning moths of the autumn has been the beautiful Merveille du Jour:

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I thought I would share a piece about moths that I entered into the RES Student Award last year…

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Waiting in the dark. The hoot of a tawny owl echoes in the depths of the wood. The Mercury Vapour lamp illuminates the Rowan, Bracken and Oak. A hunting bat clicks overhead, perhaps stealing a precious catch. Once it is pitch black and the traps have been out for some time, it is time to see what has come to visit. The effect of strong lights on moths remains a mystery. Similarly, it is often a mystery as to which species will come to the light trap. An amazingly diverse range of moth species can be found in Britain: 2,500 in total.

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Poplar Hawkmoth

Four traps are spread over one site and each trap yields something completely different. Ranging in size from the delicate and specialised Apotomis sauciana micromoth, with 7mm long wings, to the stunning Poplar Hawkmoth, 40mm long wings held carefully angled from its body. The elegant Beautiful Golden Y, the shimmering White Satin, the charismatic Elephant Hawkmoth, coloured with streaks of bright pink, the Green Carpet cloaked in waves of leaf green, the diminutive Sallow Kitten, the comical Coxcomb Prominent, both melanic and typical Peppered moths and the aptly named Scorched Wing are found amongst many others. It is a miracle how some of these moths are here on this night: the immense range of obstacles that a moth faces from the moment it begins life as an egg, to successfully reproducing are quite considerable. Of the hundreds or even thousands of caterpillars that hatch from one brood, it is often only two that succeed in reproducing as adults. But these two are sufficient to ensure the continuation of the species.1

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Elephant Hawkmoth

A moth requires a variety of habitats to survive: foodplants can differ from nectar sources, which can differ from places to shelter, breed or overwinter. When a caterpillar hatches, it needs a number of factors to thrive, including an adequate food supply of its preferred foodplant/plants and shelter to avoid predation. Unfavourable weather conditions can be a disadvantage: harsh frosts in winter and spring, and cool, rainy summers can affect eggs hatching, pupae overwintering and caterpillar growth. Interspecific and intraspecific competition from other larvae is also a challenge; some species will even consume other caterpillars. Various parasitoids will claim a small percentage of a caterpillar’s population. Disease will claim yet more. Many animals rely on caterpillars for sustenance: other invertebrates, including many kinds of beetles, spiders, wasps and ants, as well as bats and amphibians such as newts.

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Drinker moth

The amount of caterpillars that are consumed by other species is enormous. Every year, 35 billion caterpillars of different species are eaten in Britain by Blue Tits alone.2 Consider the number of other insectivorous birds that rely on this essential food source: Pied flycatchers, Willow Tits, Cuckoos, Lesser Spotted Woodpeckers and many others. Moths form an irreplaceable part of the food chain for numerous species.

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Brimstone and Green Silver-lines

Camouflage, mimicry, startle patterns, urticating hairs and aposematic colour patterns are all adaptations used by adult moths and larvae to avoid the barrage of predators and parasites they face.1 A Swallowtailed moth caterpillar mimics a slender, knobbly twig, a Merveille-du-jour will blend in with pale green foliose lichen, a Garden Tiger moth coated in long hairs discourages hungry birds, a Five-spot Burnet clearly displays its unpalatability with vivid red and black markings, a Chinese Character resembles a bird dropping and a Hornet moth perfectly imitates a stinging Hornet.

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Eyed Hawkmoth

An adult moth still faces many perils after it has successfully survived as an egg, caterpillar and pupae: there are flying predators and even collisions with traffic at night. Predation can occur in the day from birds such as Nightingales and at night from nocturnal birds such as Nightjars and many species of bat, which rely heavily on protein-rich moths to sustain them. After reaching adulthood, a moth still needs to find a mate to succeed in passing its genes to the next generation. The powerful pheromones of the female moth will draw in moths from miles away: but even if a male reaches her, she may have already mated.

After all these seemingly insurmountable obstacles, a miracle can happen: two moths of the same species can meet, mate and successfully produce fertilised eggs, continuing their line. And so the struggle for survival will begin again.

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Garden Tiger Moth

Moths appear all through the night: some flying at specific times, such as the hour before dawn. When the trappers are weary, the traps are carefully emptied into the bushes and darkness is returned to the night once more. By trapping and recording the moths on nights such as this, we can monitor their numbers and any changes over time. Declines in these important creatures will be reflected in the multitude of species whose lives are inextricably linked to them.

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Sallow Kitten moth

 

References

  1. Majerus, M. E. N. (2002) Moths. Hammersmith: Harper Collins Publishers.
  2. Fox, R., Parsons, M. S., Chapman J. W., Woiwod, I. P., Warren, M. S and Brooks, D. R. (2013) The State of Britain’s Larger Moths 2013. Butterfly Conservation and Rothamsted Research, Wareham, Dorset, UK.
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