Wednesday, 25 June 2008

Basic Introduction to the Lepidoptera

The order Lepidoptera covers the moths and butterflies. The order is second in size only to the Coleoptera (beetles). It contains over 120 families and over 160,000 described species. Australia alone has over 20,000 species.

Moth or Butterfly
An often heard question is, "what's the difference between moths and butterflies?" Well in fact, there are no taxonomic classifications that separate the two. However, some families are usually referred to as butterflies and some as moths based on some general differences. The butterflies usually have clubbed antennae and their wings are held vertically when at rest. Moths often have feathery or other non-clubbed antennae and their wings lie flat when at rest. Of course there are always exceptions to the rule.

Examples of Lepidopteran wing scales

Imago (Adult)
An adult stage moth or butterfly is also known as an imago (pl. imagoes or imagines). They have two pair of wings although in some female moths, the wings may be reduced to vestiges (brachypterous), or may even be completely absent (apterous). The name, Lepidoptera literally means scaly wings. The wings are covered in tiny scales which give them there many and varied colours and patterns. The various families are mostly separated by the wing venation, however, many families also have other traits which are easier for the amateur to notice.

Examples of Antennae

Females emit pheromones. Males, often with enlarged antennae, are able to detect these pheromones and can locate a female over a considerable distance.

There are various tactics for overwintering. Some hibernate as adults while other survive the winter as larvae or as eggs.

The adults have their mouthparts adapted for sucking with a curled proboscis. They feed on liquids such as nectar, honeydew or in some cases by piercing fruit. However, not all adults feed. Some have greatly reduced mouthparts and do not feed at all. Instead they live out the remainder of their life using up the reserves stored in the larval stage.

Egg
The first stage in the life cycle is the egg or ovum, There are rare examples of viviparous species which in fact produce live young, for example, some Coleophora spp in Europe.

Eggs of the Helena Gum Moth

Depending on species, the eggs can take anywhere from a few days to many months before hatching with some species overwintering in the egg stage. Weather conditions such as temperature, humidity, and rainfall can also effect the time of hatching. For example some species will hatch after a fall of rain as this will ensure fresh plant growth as a food source.

Eggs are usually laid on the food plant and can be found in crevices, on leaf surfaces, on flower buds etc. Polyphagous species, those that feed on a large variety of plants, are less fussy about where they lay their eggs. The eggs can be laid individually, in clumps, in neat rows or even stacked in little piles. Most eggs are covered in a kind of adhesive to stick the eggs to the surface of the foodplant and sometimes they are also covered with scales from the moth. While some species only lay a few eggs, others are capable of laying many thousands.

Larva
The larvae are usually called caterpillars. They are soft bodied with a sclerotised head capsule. The three segments of the thorax each carry a pair of legs. The abdomen consists of 10 segments. In addition to the three pairs of thoracic legs, the caterpillar's abdomen bears prolegs, which are sometimes referred to as false legs. There are usually five pairs. They are found on abdominal segments 3 to 6 with another pair on the last segment (10th) This last pair of prolegs is called the anal prolegs or anal claspers. There is usually a gap (segments 7-9) between the abdominal prolegs and the anal prolegs although there are exceptions such as the family Micropterigidae which have 8 pairs of prolegs. This gap can be used as a rough guide to separating caterpillars from the similar looking larvae of sawflies (spitfires). However, a more accurate method is to look for the presence of a ring of hook-like spines around the prolegs. These are called crochets and they facilitate clinging on to various surfaces.

Prolegs and True Legs

There is a silk producing gland called a spinneret on the labium (lower lip). Some caterpillars when disturbed will drop from their food plant attached by a long thread of silk. Some even blow in the wind attached to such a thread as a means of dispersal. The more obvious use for their silk to produce protective shelters. For example some will tie together leaves to form daytime shelters, only coming out to feed at night. Others produce cocoons during periods of dormancy (aestivation). An unusual example comes from Hawaii where several species including Hyposmocoma molluscivora have been found which tie down small snails with their silk before eating them. This is unusual in respect to the use of the silk to trap prey as well as in their carnivorous diet. The most common use of silk is is to produce a cocoon or underground cell for the protection of the pupal stage. The pupal cocoon may incorporate other materials including the hairs from the caterpillar.

The larvae are generally herbivorous although there are some exceptions. They feed on foliage, flowers, roots, and some even bore through wood. Some microlepidoptera feed on the cells between the surfaces of leaves resulting in the familiar leaf mine patterns. Note: not all leaf miners are lepidopterans. Some hymenopteran and dipteran larvae also create leaf mines. The larvae of the Pond Moth (Hygraula nitens) are aquatic and feed on the stems of water plants.

Pupa
The pupa of a moth or butterfly is often referred to as the chrysalis. With neither legs nor wings the pupa can do little more than wriggle and so it is rather defenseless. Different species use various methods of increasing there chance of survival. The most obvious is the cocoon. While the butterfly chrysalis is generally rather exposed with perhaps just a little silk to attach itself, moths will often build a cocoon. These can vary from a few very loosely woven threads to extremely tough bags which are difficult for a human to open let alone a bird. The Gum Moths make a tough a cocoon like this. When it is time to emerge, they secrete an enzyme which softens one end of the cocoon. They then use sharp spines at the base of their forewings to cut there way out.

Silk cocoons can be made between two leaves or by tying twiggy branches together. They can also be made among the leaf litter or used as a lining in an underground cell. The larvae often incorporate other materials into the cocoon. For example plant materials for camouflage or the caterpillars hairs. In the case of urticating (stinging) hairs, these can be just as potent on the cocoon as on the caterpillar. Not all moths use a cocoon. In some cases the pupa just lies naked among the leaf litter or even on the soil surface. However, the similarity in shape between the pupa and some animal droppings may in itself be a defense.

It is during the pupal stage that the adult moth or butterfly develops. This involves all but the vital organs turning into a gooey liquid, after which the adult form develops. The entire process can take anywhere from less than a week to many months. Some species use the pupal stage for overwintering. Another strategy for the overall survival of the species is for some pupae to delay development until the following year This way, if the population takes a dive one year due to cold weather, or drought etc, then they still have a second chance the following year.

Further Reading
Well I hope you got something out of reading this basic introduction. However, If you really want to know more about the fascinating lives of the Lepidoptera then here are just a few recommendations for further reading:

  • Enjoying Moths - Roy Leverton - 2001 - Poyser Natural History Books
  • Moths of Australia - I.F.B Common - 1990 - Melbourne University Press
  • Moths of Australia - Bernard D'Abrera - 1974 - Lansdowne Press
  • Flying Colours - Common Caterpillars, Butterflies and Moths of South-Eastern Australia - Pat & Mike Coupar - 1992 - New South Wales University Press
  • Common Moths of the Adelaide region - McQuillan & Forrest - 1985 - South Australian Museum
  • Butterflies - Dick Vane-Wright - 2003 - The Natural History Museum, London
  • Some Observations on the Eggs of Moths and Certain Aspects of First Instar Larval Behavior - Noel McFarland.-Journal of Research on the Lepidoptera 1973 - Vol 12(4): 199-208
  • Egg Photographs Depicting 40 Species of Southern Australian Moths - Noel McFarland.- Journal of Research on the Lepidoptera 1973 - Vol 10(3): 215-247


5 comments:

  1. A very nice entry into the world of blogging! I'm sure I will learn a lot from your site.

    It will also be interesting keeping tabs on what populations are maintaining a foothold and what may be suffering due to a changing environment in both Tasmania and Victoria.

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  3. Thank you Junior Lepid and yes is is an interesting subject as I expect we may well end up with some new migratory species reaching Tasmania in the years to come.

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  4. Thanks for the info on my "Twisted Moth" - a good name for it.
    As Junior Lepid said, welcome to the world of Blogging.
    I frequently write about Moths, as my location , in Robertson is surrounded by wet rainforest, with many plants of ancient origin, having evolved before those gaudy, greedy things called birds evolved. Hence flowers are often small and pale coloured,and scented - just to suit the moths. I do not have the books you refer to , and instead have to rely on the Web reference material. But the field is so huge, that nothing can cover it all, it seems.
    I look forward to checking out your new entries as they develop. Love your blog title!

    Cheers

    Denis Wilson

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  5. Thank you Dennis - glad I could help. I'll be keeping en eye on your blog for any moths you happen upon :-)

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