Egg or plant seed?
Stick insects are more closely related to plants than we know. Not only are they cleverly disguised as plant material but their eggs look like plant seeds. Acacia seeds have a small appendage called an elaisome which is full of nice tasting food for ants. As you would expect, ants collect these seeds and eat the elaisome while leaving the seed alone in their underground nests. After a few months the ants move to a different nest and leave the seeds to germinate when it is time.
Why should a plant encourage ants to collect its seeds? Simple really, for survival. You see the Australian bush has evolved to cope with bush fires. The eucalyptus oil in the trees fuels the fires started by lightening and other natural events. Some native Australian plants have adapted to these severe conditions and produce seeds that germinate only during the extreme heat of a bushfire. If left out in the open the seeds would burn to ashes, but underground in the nest of ants the seeds are protected and can germinate in the heat.
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Stick insects, totally independent of native plants, evolved a similar way to encourage ants to collect their eggs. This is called convergent evolution, where two different species, native trees and stick insects, have independently evolved similar ways of protecting themselves. Stick insects have eggs with an appendage (similar to an elaisome) that is full of delicious food for ants. Ants take the eggs back to their nest and store them as a food source. In the ant’s nest the eggs are safe from predators and bushfires. However, what happens if the eggs hatch while in the nest? Ants are formidable opponents that violently guard the nest from intruders. This is not a problem as the ants vacate their nest every 6 to 8 months, leaving the eggs to hatch. Stick insect nymphs (juveniles) are very good at digging their way out.
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What benefit is it to the ants to collect stick insect eggs? Explain the benefits
of tricking ants into
Are there any other species
that have independently evolved identical ways |
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