By Andrew Deacon
Rene Poultney of Expressions of Africa in Skukuza presented me with a bowl of "worms" (see photo) one morning, enquiring what they are. A branch of an old umbrella thorn tree (Acacia tortilis) that died about a year ago in front of their offices broke off and nearly collapsed on the building.
The exposed areas revealed a lot of tunnels in the wood and masses of pulp and chewed wood. From the tunnels these grubs appeared and she collected them. With a lot of help from Guin Zambatis of the Skukuza herbarium, it was decided that these grubs are the wood-boring larvae of longhorn or timber beetles. In Afrikaans they are known as "boktorre" or "langhoringkewers".
The adult longhorn beetles are called such due to their characteristically long antenna, usually at least two-thirds of their body length. According to Guin these grubs are probably the larvae of the large brown longhorn (Macrotoma).
The large brown longhorn is a nocturnal beetle that is up to 50mm long and is attracted to lights at night. Eggs are laid in cracks in dead or living timber. The large white grubs feed as they tunnel into the wood of decaying robust thorn (Acacia robusta) or umbrella thorn trees (Acacia tortilis).
A single tree sometimes becomes so infested with these larvae that the inside is wormsriddled with wide tunnels. Larvae possess an enzyme for digesting cellulose, and as the grubs eat their way through the wood, they pass cream-coloured faecal pellets which become tightly compressed in the tunnel behind them. These larvae, known as mabungu grubs, are a great delicacy in some regions when fried, having a taste reminiscent of roasted peanuts!