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Hypothesize This: What’s With All The Moths in Vancouver?

Hypothesize This is a monthly series looking into trends, buzzwords and other phenomena with the curiosity of science. This month, local Vancouverites took to Reddit to post about a noticeable surge of moths downtown and its surrounding area – but what observations can we make from this compilation of photos and comments around the city? Is it a recovering population? Are they invasive or friends to our ecosystem? What benefits do moths provide to our urban environment? We sat down with natural scientist and Visitor Experience Manger, Dale Minchin, to discuss some theories on why we might be seeing a boom of these winged critters.

Where do we start when analyzing this phenomenon?

Observation is super important – I mean, it’s the basis of science. Looking at these creatures, observing them and looking for patterns is a good first step. Let’s take a look at a moth I found outside our building. Very cool zig-zag patterns on the wings, hey? Moths are classified as Lepidoptera, which butterflies also fall under. Like most insects they have four wings. Lepidoptera have two back wings that are hinged and hooked onto their front wings. If we looked at their wings under a microscope you’ll see lots of little scales which is what “Lepidoptera” means: scaled wing. If you’ve ever touched a butterfly and get that dust on your fingers, that’s the little microscales. I always think of them like sequins on a dress.

What do the scales help them do?

It helps them aerodynamically which basically allows them to flutter and fly. Some Lepidoptera can fly great distances. Monarchs, for example, can fly from here to as far as Mexico which is astounding

What distinguishes a moth from a butterfly?

Moth and butterflies both have six legs and two antennas but moth antennas are often really frilly. You can speciate a moth by counting how many branches there are on its antenna, which you’ll need a microscope to do. Moths use their antenna to perform pheromone detection, which is like smelling, as well as feeling and hearing. Some can actively detect ultrasonics which is super cool. Like most insects, they also have compound eyes, which mean they have a different sense for lights. That’s why you see them flying towards the light bulbs. They use moonlight to navigate, which is pre-instinctual and pre-programmed in them because of their short life span. So, if we didn’t have the light sources that we do in the city, they would be following the natural light sources of the night.

So can we tell if this population boom is a one-off event or a troubling ecological pattern?

It’s complicated but we can make some hypotheses. Because of the controls humans do to manage wild ecosystems, you never really know. An abiotic factor, which is a non-living condition like the weather, can sometimes contribute to a sudden population surge. Mosquitoes are a classic example of this. When you get a lot of rain in warm weather early in the summer, mosquito populations boom because there are puddles everything. Mosquitoes also have a two-staged life-form which is the same with Lepidoptera. Moths have the caterpillar form and then metamorphisizes into the adult form. Which means if we have a lot of adults, which is what we’re seeing now, then we had a lot of larva. These are organisms that are finished their eating phase. As plants are dying back and we get closer to the Fall, they enter a dispersal phase. Which means moths are flying all over the place, looking for places they can lay eggs over winter.

What would the larva have affected?

Probably a lot of the community gardens in the city. We’re also in an interesting time because a lot of global transportation vectors are introducing a lot of new insects around.

There was an aerial spray for an invasive species of moths in the Surrey area this past summer. Could this have contributed to what we’re seeing now?

Actually, that would have contributed in a decrease in the general insect population. Aerial sprays target the larva form with a bacteria that attacks the gut of the Lepidoptera. Unfortunately, it’s tough to specifically target one species so this ends up being a very general spray that wipes out a lot of butterflies and native moths. In processes like these we would see a crash in insect populations which have been happening for a long time.

Are aerial sprays the only way to get rid of an invasive population of moths?

Actually, another way to hold invasive populations at bay is just by having a healthy ecosystem. The reason why invasive species, mainly plants, have been able to thrive is because we have many disturbed sites. Primary colonizers like the Japanese Knotweed and the Himalayan Blackberry enter empty field lots and transform them. If we had a healthy ecosystem with lots of plants like ferns, moss and local trees all around there would be no space for these colonizers to put roots and start and invasive spot. Establishing a non-disturbed ecosystem can protect and create a good barrier for evasive species from spreading.

What do we know about moths?

There’s a lot of unknown science in this area. For every different beetle out there we're researching, there are hundreds and thousands of moths. You definitely don’t hear someone in an important meeting going, “Good God! We need Lepidoptera now!” It’s really the very passion of citizen scientist and entomologist, who are few and far between. What moths do and what their behaviours are generally less studied because unless it’s a problem moth who are eating crops or in our wool sweaters. People are studying the coolex mosquitoes because they’re carrying the West Nile virus and asking “How can we control them?” With moths, we're not as curious.

But we do know that they are part of the nocturnal food chain. They are feed for animals like bats. Some moths have the ability to mimic echo location which act almost like a jamming signal, sending a click that will confuse bats. Those kinds of moths have developed what’s called an evolutionary competitive strategy where an animal that’s hunted evolves with defence mechanism that will prevent it from being hunted.

What’s your best hypothesis of what’s happening in the city?

Often times, insect populations are cyclic. Cicada populations, for example, boom every seven, eight or nine years depending on the species - not because of abiotic factors but because of some sort of biological element. That could be a similar kind of trend that’s happening here with moths. Watching for a healthy diversity of moths show that the ecosystem is doing well. You can do an experiment at home with what’s called a harp trap. Any insect attracted to the light drops into the trap’s little fold at the bottom and you can look and see what you caught.

And then what do you do with the ones you’ve caught?

You let them go. Unless you’re an entomologist who wants to send it off for research or name a new species.

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