All insects go through some form of larval stage during their development. Their life cycles can be divided into two categories. Holometabolous species have a larval stage of growth then a pupal stage during which it undergoes metamorphosis into the adult form. Butterflies are a typical example - caterpillar then chrysalis to adult. Hemimetabolous species undergo a gradual change to adult form through a series of larval stages known as instars.
The vast majority of guide books concentrate on the identification of the adults of insects. But the collection and identification of insect larvae can be equally enjoyable. The surveying of larvae is also important to environmentalists monitoring insect populations. Indeed many insects spend most of their lives as larvae and only a relatively short time as an adult. Larvae are important in the understanding and protection of insects as larvae can inhabit a completely different ecological niche to their adult form.
Dragonflies & Damselflies
The larval stages of dragonflies and damselflies are aquatic predators generally found in unpolluted, well oxygenated freshwaters. They prefer vegetated areas in which they can use plants as a platform for hunting and to hide from their predators such as fish. Both dragonfly and damselfly larvae are hemimetabolous and so wing buds develop during their larval stages or instars. The can be initially distinguished by their abdomens (tail end). Damselflies typically have 3 flattened plates at the end of their abdomen that are in fact gills. Dragonfly larvae have a more rounded abdomen that ends in just 3 or 5 small points.
Collecting dragonfly and damselfly larvae is fairly simple using a pond dipping net. They are relatively large aquatic invertebrates and so a mesh of 1 or 2mm is suitable. They can be collected by simply dragging a net across the bottom of a lake or riverbed. A white tray is useful for sorting your catches and a magnifying pot or hand magnifier is a good way to get a good look at their finer identifying structures such as gill plates. The British Dragonfly Society’s field guide to dragonfly larvae is an excellent photographic guide that provides clear identification aids without the use of scientific keys.
Butterflies and Moths
The larvae of butterflies and moths, more commonly known as caterpillars, are typically terrestrial herbivores. In contrast to dragonfly larvae they are holometabolous and so show no gradual change into adult form but a complete metamorphosis in the pupal stage or chrysalis. Butterflies and moths tend to have specific plant species on which they lay their eggs and on which the caterpillars feed. Larval Food Plants of the Butterflies of Great Britain and Ireland provides a handy references to what caterpillars can be found on what plants.
Caterpillars can be simply collected by hand from ground vegetation and shrubs. But always take care which you handle as some hairy species can cause serious skin irritations. Many species of caterpillars are found in tree foliage and so are more difficult to sample. Beating trays can be used to help collect arboreal species. The large fabric tray can be held under a tree and the leafy branches beaten with a pole. This can knock down caterpillars that get caught on the tray and easily spotted for identification.
Sweep nets can also be used to collect caterpillars in grassy habitats or other non-woody ground vegetation. Dragging one of these robust material nets through vegetation knocks off all sorts of insects including caterpillars and collects them in the bag for sorting and identification. However you choose to collect caterpillars a set of forceps will be useful to safely handle any caterpillar you catch. A hand lens, magnifying pot or hand magnifier will be handy to get a close up look at your subjects. An identification guide is essential tool for beginners and the more experienced alike. These range from large comprehensive guides such as the Colour Identification Guide to Caterpillars to handy fold-out FSC charts that can easily be slipped into a backpack.
