A reader wrote to us recently about a worm, or what is believed to be a worm, with the follow characteristics: (1) The worm is big, about 20 cm long and as thick as a “man’s thumb”; (2) the worm has lots of spikes, or what look like spikes, on its back; (3) the back of this worm also has white dashes on it; (4) the worm has an orange line that runs down it side; (5) the worm was found in the reader’s grass in Port Elizabeth, South Africa.

So, the question is: what type of worm is this?

Well, it’s hard to say. The first thing to be said about this worm is that it may not be a worm at all. In fact, based on the description above, it sounds a lot like a caterpillar – that is, the larvae of butterflies and moths.

Worms and caterpillars share a number of characteristics, so it can be hard to tell them apart. Many species of worms and caterpillars have cylindrical bodies that are segmented, and both serve as a food source for many animals. Because they serve as a food source for other animals, some types of worms and caterpillars have defense mechanisms that help them ward off predators. These characteristics, along with a host of others, make it hard to tell the difference between worms and caterpillars. So, it’s altogether understandable that our reader confused the two.

However, even assuming that the long, black, spiky creature described above is in fact a caterpillar, this doesn’t limit our search very extensively, as there are more than 20,000 known species of caterpillar, and there are believed to be many more undiscovered species in the world. We found a couple of caterpillars that roughly resembled the species described above – the Grammia arge, the larva of the arge moth, as well as the Cucullia alfarata, the larva of the Camphorweed Cucullia moth – but neither of these was a perfect match, and besides that, both of these species are found in North America.

Unfortunately, we must ultimately say that we are unsure what worm or caterpillar the reader found in the yard. However, we can point him or her to this helpful website, which allows you to search through some species of caterpillar on the basis of their characteristics.

Here is the website: http://www.discoverlife.org/20/q?guide=Caterpillars

Hope that helps!