Insects Have Two Major Paths In Their Life Cycles
In general, insects will develop from eggs to adults in one of two ways. Hemimetabolous or incomplete metamorphosis has only three stages being egg to larva to adult. The second method is called Holometabololous or complete metamorphosis where there are four stages in the life cycle being egg to larva to pupa to adult (Britton 2009).
In general, insects will develop from eggs to adults in one of two ways. Hemimetabolous or incomplete metamorphosis has only three stages being egg to larva to adult. The second method is called Holometabololous or complete metamorphosis where there are four stages in the life cycle being egg to larva to pupa to adult (Britton 2009).
1. Hemimetabolous
In this life cycle (Fig. 1), the eggs hatch into immature larvae forms (more correctly called nymphs). The nymphs gradually grow in size and after each shed of the exoskeleton (referred to as moulting) the insect looks slightly different until after the final moult it transforms into a full adult (Britton 2009). |
Insects in this group include:
1. Hemiptera (Scales, Aphids, and Cicadas) 2. Isoptera (Termites) 3. Orthoptera (Grasshoppers and Crickets) 4. Phasmatodea (Stick Insects) 5. Mantodea (Praying Mantids) 6. Blattodea (Cockroaches) 7. Psocoptera (Wood Lice and Book Lice) 8. Dermaptera (Earwigs) 9 Odonata (Dragonflies and Damselfies). |
2. Holometabolous
In this life cycle (Fig. 2), the eggs hatch into larvae which are commonly called maggots, grubs or caterpillars. As with the nymph stage, the growth in size is accompanied by several moults but there is little change in appearance. When the larva is fully grown it metamorphoses into a pupa stage by either wrapping itself into a cocoon or evolving into a chrysalis and it finally emerges into its adult form which is spectacularly different from its larva stage (Britton 2009). |
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Insects in this group are often termed higher order insects and include:
1. Diptera (Flies) 2. Hymenoptera (Sawflies) 3. Coleoptera (Beetles) 4. Lepidoptera (Butterflies and Moths). |
Glow worms are the larvae stage of a small fungus gnat or fly (Arachnocampa luminosa and Arachnocampa flava). "Arachno" is a reference to its ability to spin silk threads and "campa" is a reference to its grub-like appearance. A. luminosa is found in New Zealand and A. flava lives in Australia (Meyer-Rochow 2007).
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Life Cycle of Glow Worms
Each species lays up to 130 tiny eggs. A. luminosa eggs can be up to 0.75 cm while A. flava are much smaller in diameter. In the colder New Zealand climate, the eggs hatch after 20-24 days. The eggs of the Australian species living in warmer temperatures hatch between 7 and 9 days. Glow worms remain in this larva stage for as short as four months but more generally between nine and twelve months depending upon environmental conditions and abundance of food (Meyer-Rochow 2007).
Image by Anthony O'Toole.
The larva spins a silk and mucous tube in which it lives and several silk threads hang down from the tube with sticky droplets of mucous to trap its prey. Glow worms group together in large colonies often in caves or sheltered forest habitats. Each larva emits a small amount of light. By massing together, the light is stronger and increases the attraction of other species of small flying insects on which the glow worm larvae feed.
When the larvae are fully grown, they enter the pupae stage which lasts 12-13 days for A. luminosa and 6-7 days for A. flava. They then emerge from their pupal cases as adult flies. The lifespan of both species is similar, females live between 2-3 days and males live to a maximum of 6 days. Females are larger and have flatter abdomens due to the eggs that they carry. The adults' only purpose is to reproduce. As a result they are poor fliers and their degenerate mouths prevent the adult from feeding (Meyer-Rochow 2007).
When the larvae are fully grown, they enter the pupae stage which lasts 12-13 days for A. luminosa and 6-7 days for A. flava. They then emerge from their pupal cases as adult flies. The lifespan of both species is similar, females live between 2-3 days and males live to a maximum of 6 days. Females are larger and have flatter abdomens due to the eggs that they carry. The adults' only purpose is to reproduce. As a result they are poor fliers and their degenerate mouths prevent the adult from feeding (Meyer-Rochow 2007).