I’m an insect and I’ll eat you!

By Kim Pullen – Australian National Insect Collection

Often when we see insects, their feeding is what has brought them to our attention. Weevils in the pantry, silverfish in the library. Caterpillars eating the tomatoes. Ladybirds doing a good job on those aphids. Mosquitoes tormenting us at the garden party.

Insects, like all organisms, need energy to live and function, and they get that energy from food. One way to make sense of the myriad of food habits animals have is to divide them into three groups: carnivores, that eat animals; herbivores, that eat plants, and fungivores, that consume fungi.

Although the typical image of a carnivore is that of a ferocious predator, this is only one way to get a ‘meat’ meal.

Praying Mantis eating prey

A Mantis’s keen eyes, trap-like legs and lightening reflexes mean a quick death for unsuspecting prey. (Image Paul Zborowski)

A predator kills its prey, but then it has to go looking for more, which can use a lot of energy. Why not simply attach yourself to another animal, or get inside and feed off its fluids?

Robberfly sucking juices out of cicada

This Robbefly has caught a Cicada bigger than itself, and is busy sucking out its juices. (Image E.Zillmann)

Food when you want it, for less work. This is parasitism, a second kind of carnivory. Parasites feed off another animal (the ‘host’) without killing it – although the parasite may transmit a third, more deadly organism, such as when a mosquito transmits malaria, another parasite.

Some groups of insects fall somewhere between predator and parasite in their way of feeding. They are like parasites, but eventually kill their host, literally eating it alive until nothing is left.

A parsitoid wasp inserts an egg into an aphid

A parsitoid wasp inserts an egg into an aphid

Many wasps follow this pattern, and they are termed parasitoids. The mother wasp searches out a luckless host and may paralyse it with a sting. In some cases the paralysis is permanent, and the wasp drags the prey to its nest, lays an egg on it, and seals the nest.The egg hatches into a maggot which consumes the host over a period of weeks or months, eventually emerging from the nest as a new adult.

In other cases the wasp simply inserts an egg in the host and leaves. The hatching maggot consumes the insides of its poor host, taking care not to eat any essential organs until last!

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