Moths: Night dancers and environmental indicators

Monitoring lepidoptera - Stage 2 of the project plan

November 2024

Poecilasthena pulchraria | native cranberry moth

When you Google 'moth traps' in New Zealand, it recommends a lot of ways to kill our nocturnal companions. There are only a handful of people across the country to whom it means a way of studying nocturnal insect life. When so few people, even those interested in nature, are familiar with our native butterflies, moths are simply a step too far. They are the attackers of wool jumpers and the unwanted additions to the pantry. What they are not is cherished.

I am the proud owner of a moth trap, brought over from England by parents with a luggage allowance as vast as their carbon footprint. I had been heading out into the local bush at night with a head torch, but it's scary for a lone female and moths are hard to identify on the wing. A moth trap means they come to you. You just have to get up at dawn instead.

In the project plan for my garden transformation, I want to see how the changes I make to the plant selection makes a difference to the range of butterflies and moths, so #2 on the to-do list is:

2. Need to start butterfly counts and moth trapping to establish a baseline.

Moths change through the seasons and I am not waiting a year before starting the transformation of my garden so one could legitimately argue it's not good science. One would be pedantic, but one would be right.

Yes, I know the experts say to leave it a year to get to know how your patch evolves with the seasons, where the light falls, how the soil fares, but they are probably not impatient introvert gardeners with no flowers to enjoy. However, in planting saplings and seedlings, I am not going to make a fundamental difference in the first year, so it's a good enough base line. I hope to see an expansion of species with a broadening of the plant range in the garden because moth and butterfly larvae can be plant specific.

To give at least the appearance of scientific legitimacy, I undertake moth trapping on the last Saturday of each month, weather permitting, in the same place. I have a plug in UV light, so it's on the back deck overlooking the stream and bush area.

A simple moth trap overlooking the bush

Since we moved two months ago I've already recorded 59 species of lepidoptera, 56 of which are moths. I have a simple moth trap - its light and portable - but it has a 20w UV bulb, less powerful than more professional traps, and my design is easier to escape, so it's never going to be a full reflection of the local night life. However, it will allow at least a consistent monitoring approach.

Moth trapping is like Christmas morning  -  you don't know what you are going to get inside until you open it up. This month's trapping turned up two very special guests - a male and female puriri moth - the first I'd ever seen in my 20 years in New Zealand.

So fluffy!

Puriri moths are the largest of our 2000+ moths with a wingspan of up to 15cm. They are found in North Island forests. They are adults for only a couple of nights in which they will mate and lay eggs. That is, if they don't become food for ruru (our most common owl) or introduced mammalian predators. Their larval stage is about 5 years and then they pupate for 4-5 months in burrows in native and non-native trees, which in turn provide safe habitats for wētā once the moths emerge.

Male puriri moth

What about butterfly counts? Unfortunately there have been so few I haven't done it systematically. I saw a common blue butterfly the very first week we arrived, but no more since. A pair of cabbage white butterflies visit the garden every day, but there's nothing to interest them. Since I arrived here two months ago, I have seen a monarch butterfly in my garden exactly once. They are not in the neighbours' gardens either. In my last garden 10 minutes' drive away, I would have at least three monarchs at all times around the plants in the front bed during summer. I couldn't fit in many plants, but nothing was grown that didn't feed butterflies, birds or bees. In this new garden, just a smidgen short of half an acre  - three times the size of the last  - I have space for a lot of plants, but no butterflies. I do probably have three times the bird life, but that's a story for a different time.

So there's a lot of work to do to bring the butterflies in and in the meantime, I'll enjoy the moths that silently dance through the night.