For a long time now we had noticed piles of what appeared to be sawdust at the base of a large native tree. We blamed this on our neighbour, who has been known to reach over the fence and lop off overhanging branches. Then when we had some branches trimmed several months ago we were horrified to find them riddled with very large holes by some sort of burrowing insect. Closer inspection of our trees showed that two of them had holes throughout the trunk and branches. What kind of insect could do damage on this scale we wondered? Let’s just hope that whatever it is stays outside and doesn’t decide to infest our timber house! We had visions of giant sized borer all ready to attack.
The mystery was solved with a phone call from our friend Calvin. “Go and buy the newspaper”, he told us, “and you will see what is making those holes in your trees”. According to the newspaper article, the culprit is the giant puriri moth, a large green moth with a wing span of 15cm, that’s six inches across. The eggs are scattered on the ground under trees where the young caterpillars live amongst the leaf litter. They then climb the tree and bore into the trunk, going in at a right angle then turning 90 degrees to burrow down lengthwise. The caterpillars live in the tunnel and are thought to have long lives of up to seven years. They induce the tree to produce callous tissue which they feed on, and protect the tunnel entrance with a tough silken cover. When they finally emerge as a moth, they live just two days in order to mate and lay eggs. This hardly seems fair after their exceptionally long life as a caterpillar.
Photo courtesy of Landcare Research
The holes in the trees are obviously where the puriri moths finally emerge from and fly away. Luckily the grubs feed on living trees so it seems unlikely that they will come and share our house with us. Amazing that all this has been going on under our noses and we knew nothing about it until now!!