Odonata

Order

ODONATA
(Greek, odous = tooth)

Description

All adults have short antennae composed of straight segments (filiform) and prominent compound eyes; simple eyes (ocelli) are usually present. The mandibles are well developed and all adult species are predatory on other aerial insects. The legs are used to capture aerial insects by forming a "basket" in which the prey is first secured then transferred to the insect’s mouth. The two pairs of wings are large, membranous and equal in size with prominent venation. Damselflies and dragonflies are very similar in appearance but differ as follows: at rest, the wings of dragonflies are spread out perpendicular to the body (resembling aircraft wings), damselflies bring their wings together loosely over the back of the abdomen; dragonflies tend to be more strongly built insects, damselflies tend to be rather delicately built; dragonfly nymphs are heavily built mud-dwellers, while damselfly nymphs frequent tangled vegetation at the sides of the stream or pond and have two flattened abdominal appendages which are absent in dragonfly nymphs. The juveniles emerge from the eggs as a wingless forms of the adult (nymph). However, the overall body shape may be much shorter and robust. A feature of dragonfly nymphs is the extendable lower lip (labium) or mask which is equipped with pincers. The labium is thrust forward very rapidly to capture prey. As they develop, dragonfly nymphs become capable of securing quite large prey including tadpoles and small fish. During development through a number of moults, wings begin to appear, but these are non-functional. At maturity, the nymphs move to the surface and emerge onto reeds or similar surfaces. The adult emerges by breaking through the nymph’s final exoskeleton.

When in the aquatic phase, any suitably sized animal is captured for food. This may include insects, tadpoles, fish, mosquito wrigglers, etc. Once the adult form is reached, most food is captured in flight and consists of other winged insects, particularly those associated with ponds or streams.

Odonata is a very ancient order of insects with fossils dating from the Upper Carboniferous. Some species from this time period had 70 cm wingspans. Dragonflies and damselflies form an extremely important group of predacious insects in stream and pond ecosystems. They are responsible for population control on a number of associated insect species. The adults are quite long lived and consume large quantities of insects over many weeks.