Nature Walk: Insect oracles

Clockwise from top: black-and-white fishfly (Nigronia serricornis); cabbage white butterfly (Pieris rapae); white-striped black moth (Trichodezia albovittata). (Illustrations by Anita Barbour)

Clockwise from top: black-and-white fishfly (Nigronia serricornis); cabbage white butterfly (Pieris rapae); white-striped black moth (Trichodezia albovittata). (Illustrations by Anita Barbour)

To all appearances this was a bad spring for moths and butterflies. Our porch light and lit-up windows have attracted fewer moths, and fewer species of moths, than any May and June in 30 years. Butterfly numbers have been down as well, making both night and day far less lively than usual. This has been a really depressing observation to me.

Curious as to whether other lepidopterists were in the same doldrums, I queried a few colleagues. From down near north Jersey to up Ithaca way the stories agreed — a widespread scarcity of butterflies and moths was upon us.


But though this lack of Lepidoptera and other flying insects held generally, there were exceptions. A few species and ecologically-related groups were more numerous than usual.A common observation that grass-loving moths were often stirred up from lawns reminded me that I had seen one of these turf moths, a showy little thing called the white-striped black (Trichodezia albovittata) in good numbers in early June. In most years I’ve had only a handful of single sightings for less than a week. This year their flight was a little longer, with one to four per day, often two at once.

Exceeding the white-striped black in abundance were black-and-white fish flies (Nigronia serricornis, insect order Trichoptera), a big hatch from our little stream, often five or six at a time. Other aquatic insects, such as damselflies and dragonflies were also common, indicating that water was a good place to overwinter.

By contrast, the typically prolific cabbage white and common spring azure butterflies were scarce, and the common yellow sulfur and American painted lady simply failed to show. One friend had seen one sulfur just last week. Also absent were falcate orangetip, pine elfin and olive hairstreak. These butterflies, though scarce in many places, have nearly always been present in May in our back yard.

On most nights this spring, the house lights were bare, and this hardly changed as summer arrived. A good night might lure in a few small moths, and occasionally one with a wingspan of about an inch. There were also a few stream insects — caddis flies, alderflies and midges, neighbors of the diurnal fish flies of May. Mayflies were also very scarce this year.

A few colleagues hypothesized about possible causes of differences in numbers among various flying insects. My friend John Yrizarri, a lifelong observer of insects, was the most personal and thoughtful. He’d been keeping moth records continuously, even through the winter, observing a few moths at his light on only the three warmest nights. In April, May and June so far, he saw only one or two moths on any night, and on many nights none. A neighbor found a luna moth one night, John’s only noting of that much-noticed cocoon-spinner.

John surmised that the winter’s harrowing cold, depth of frost, and late lingering chill took their toll among insect; how much depended on their habits and habitats. Suffering severe losses were insects with fragile or highly exposed overwintering stages, such as cocoons, shallow-situated pupae, and hibernating adults. Both extended cold and hunger-stressed predators likely took a heavy toll on such vulnerable moth species.

As to why moths continue to lag, John said to consider how cool the nights have been so far this June. With nightly temperatures in the 50s, even in the 40s some nights, why would moths bother to fly? They are better off waiting for warmer nights, when they can be active while expending far less energy. John thinks that when nights get warmer the moths will show up in greater numbers.

On the other hand, though nearly all our resident butterflies appeared late this year, as John and I both observed, the early summer fliers are catching up with the season. Tiger swallowtails lagged a little behind, but more of them are flying as the days heat up. Hairstreaks, tiny social butterflies that gather together and squabble over perches on sunlit tree leaves, just started to emerge this past week. Over the weekend red admiral butterflies appeared, perfect and freshly emerged, hopefully heralding the emergence of red-spotted and banded purple butterflies in the next week or two, right on time.

Migrant butterflies, such as anglewings, seem to have cautiously waited a few weeks before safely settling in at our latitude from points farther south where they had overwintered. It was only last week that I saw the first migrant of the year, a question mark butterfly, about six weeks later than average. The Southeast suffered serious cold spells last winter, but our northern butterflies are a hardy lot, and probably survived there with ease. John says wait, there will be more.

As to longer-term biological effects of this long hard winter and more radical weather to come, time will tell. As we watch this growing season play out, fascinating responses by moths and butterflies may unfold. Some species may remain depressed for years, while others could recover spectacularly. Some lepidoptera may change their habits drastically, switching host plants or unexpectedly occupying new habitats. Whatever changes we and our airborne six-legged fellows are facing, they are bound to be surprising and illuminating.