Sunday, 30 April 2017

Wax Worms and Moths: Caterpillars That Digest Plastic Bags

A preserved greater wax moth
Photo by Sarefo, CC BY 3.0 License

A Caterpillar That Eats Plastic

The wax worm (or waxworm) is a caterpillar that feeds on the wax in beehives, among other things. Scientists in Spain have just made what could be a very useful discovery about the caterpillar's abilities. It can eat and digest the polyethylene that is used to make plastic bags. This means that it might be useful in reducing plastic pollution. Plastic waste normally breaks down very slowly and is harmful to many organisms, especially in the ocean where much of the waste collects.

The wax worm that's being investigated by the researchers is the larval form of an insect known as the greater wax moth, or Galleria mellonella. The discovery that the caterpillars can digest polyethylene was made by accident. The insects were being stored in plastic bags. The researchers noticed that multiple holes were appearing in the bags and realized that the caterpillars were actually eating the plastic. They later discovered that the insects change the polyethylene into ethylene glycol.

The Greater Wax Moth

The greater wax moth is native to Europe and Asia but has been introduced to other areas. It invades beehives as well as stored honeycombs from the hives. A honeycomb is made of wax produced by the bees' wax glands and contains hexagonal chambers that are used to store honey and pollen. The female wax moth lays several hundred eggs inside a chamber or in cracks in a hive. 

According to agricultural experts, wax moths are rarely successful in healthy beehives. They can be a big problem in unhealthy hives where they are able to reach the honeycomb without resistance from bees, however. They can also be a problem for honeycombs taken out of a hive.

The wax moth's eggs hatch into larvae, or caterpillars. The larvae are white, brown, or grey in colour. They form tunnels in the honeycomb by chewing through the wax. They line these tunnels with a web of silk.

Eventually a larva surrounds itself by a silken cocoon and becomes a pupa. Inside the pupa, the larva undergoes metamorphosis and becomes an adult. The moth leaves the hive and breeds, enabling the life cycle to begin again. 

Digesting and Recycling Plastic 

The plastic bags used to package store goods for consumers are usually made of polyethylene. The ability of wax worms to digest the polyethylene could be very helpful. Researchers don't yet know whether the caterpillar is digesting the plastic with enzymes that it produces or whether bacteria in its gut are doing the digesting, as happens in Plodia interpunctella. This is another moth whose larvae eat wax from honeycomb. It's classified in the same family as the greater wax worm and is commonly known as the Indian mealmoth. Other researchers have discovered that the larva of a particular beetle can digest plastic. The lesser wax worm eats beeswax, but as far as I know researchers haven't explored whether it can digest polyethylene.

Reducing the use of plastic bags or at least recycling them is an important process right now. Some stores are charging for plastic bags to reduce their use. Although curbside recycling programs generally don't accept the bags, some places do. A supermarket near my home has a collection bin for recycling plastic bags, for example.

In the near future, we might be recruiting specific insects and bacteria to break up our plastic. This almost certainly won't reduce the need to reduce the creation of plastic pollution, but it could be a great aid in removing the waste that has been or is created.


A new solution for plastic waste?
The greater wax moth

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