Recently, a reader wrote to us from Bronberg Ridge in Pretoria. She states that she saw some worms on the leaves of her haak-en-steek Acacia tree. These worms were hanging, suspended on a thread, from the branches of the tree. The worms had no hairs, were pale green, and were about 20 mm (a little more than ¾”) in length. She wonders if we know what these creatures are and if she should be concerned about them hurting her tree.
We love questions like this, because they allow us to learn things that are a bit outside our comfort zone. First, let’s look into the location. Knowing where a reader lives helps us to figure out what creatures are common to that area. In this case, we’re not sure where Bronberg Ridge in Pretoria is located. A quick google reveals that it is in the Gauteng province of South Africa. This is the second question asked by a South African reader that we’ve answered this week!
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The next thing we need to determine is what type of tree we’re talking about. It turns out that the term “haak-en-steek” is the Afrikaans name for the umbrella thorn acacia tree (Vachellia tortilis).
Since our reader was concerned about the critters damaging the tree, our first step is to investigate if there are any insects or caterpillars that specifically target this type of tree. According to a report released by the World Agroforestry Center, there are several species that can threaten Vachellia tortilis. These include the powder pest beetles (Sinoxylon anale and S. crissum), the Callosobruchus chinensis, and the Caryedon gonogara (bruchid). The report also notes that it can be susceptible to “attack by other beetles, caterpillars and blight.”
The good news is that none of the specific species mentioned above look anything like the reader’s description, so it’s unlikely that she’s seeing those.
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Her description sounds like a caterpillar, so our next step will be to see what types of caterpillars are native to her area of the world that might like to feed on Vachellia tortilis. According to AfroMoths, there are 13 different species of moths that both live in the Gauteng province of South Africa and consider Vachellia tortilis to be a yummy snack. These include members of the families Erebidae, Gelechiidae, and Geometridae. The caterpillar she’s describing could come from any of these families, so we really can’t narrow it down much from there. However, except for the beetles mentioned above, we don’t think that any of these will threaten the life of her tree. To remove them, she should go out in the evening, pick them off by hand, and simply move them to another location.
If the tree seems to be ailing, or just for peace of mind, we recommend contacting a local tree or pest-control expert. They will know the pests common to that area, how to control them, and if any are a threat to her Vachellia tortilis.