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White Underwing Moth

 

 

 

 

 

Biology of the White Underwing (Catocala relicta)

By Doug Collicutt

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Description

The White Underwing is a fairly large moth, with a wingspan of 7-8 cm. The stout body is mostly white owing to a dense covering of white hairs, while the top of the abdomen and thorax are black. The tops of the forewings (the wings toward the front, or head-end of the moth) are white with black and cream coloured blotches and wavy lines. The tops of the hind wings are black with broad white, arching bands. The bottoms of both wings have alternating, arched bands of white and black. White underwings have long spindly legs and long, thin antennae.

Classification

Here's the formal taxonomic classification of the White Underwing.

Name

The White Underwing doesn't get its name from having white under its wings. The common name derives from it being a white-coloured member of the group of moths known as underwings (Genus: Catocala). Most underwing moths are grey or black on the top of the forewings. The term "underwing" refers to the brightly coloured hind wing that is hidden under the drab, camouflaged forewing. When startled or attacked, underwing moths raise their forewings and flap to escape, exposing the brightly coloured hind (under) wings. The bold markings are thought to confuse or startle predators, or cause them to aim their attack at the hind wings, the least important part of the moth's body. Even a momentary distraction can be enough to save a moth from becoming bird food. Other common names for the White Underwings are Forsaken Underwing or the Relict.

The scientific name for the White Underwing breaks down as follows, I think!

Catocala: "Cat" derives from the Greek "kata" meaning downward or underneath. "Cal", from the Greek "kalos" means beautiful. So, the Genus: Catocala could translate to "underneath beautiful", a reference to the attractive "underwings" of this group of moths.

relicta: From the Latin, "relictus", which means forsaken, lost or abandoned, a clear reference to the other common names of this species. Though, how they acquired their other common names, I could not track down.

Habitat and Range

This appears to be a moth of the northern deciduous forests of North America. As its caterpillars eat the leaves of deciduous trees and shrubs, these must be present in an area for the species to persist. It occurs across Canada and as far south as the central United States. White Underwings are common throughout southern and central Manitoba, but how far north they occur isn't known.

Food

Caterpillars of the White Underwing eat poplars (Genus: Populus) and willows (Genus: Salix). I couldn't find out what, if anything, that the adults eat, though they likely nectar at available flowers.

Life Cycle

Adult White Underwings emerge from their cocoons in late summer, late August to early September, and mate. I assume that they lay their eggs in the fall on the branches of the appropriate host plants for the caterpillars. The eggs then hatch in the following spring. How long it takes for the caterpillars to reach maturity and how long they pupate for is anybody's guess!

The caterpillar of the White Underwing is well camouflaged, too!

Camouflage and Not Being Eaten

It would be very difficult to notice a White Underwing moth on the trunk of a birch or aspen tree, which is what helps to keep these moths alive! The mottled colours and wavy lines help to break up the outline of the moth and help it to blend into the background. It's interesting, though, that their camouflage derives from the top surface of the forewing only. The underneath of the forewing and both sides of the hind wing are boldly patterned and highly visible. But in this moth's normal daytime resting position, against the trunk or branch of a tree, the tops of the forewings are all that are exposed for predators to see. This makes their "startle" defense when they are encountered by a predator even more effective. If a bird or other predator is uncertain of the exact size or shape of its potential meal, it is all the more likely to be startled or confused by the bright, flashing "underwings". And an instant is all it may take for the moth to make it to freedom. Many other Manitoba moths are masters of camouflage. Some look like tree bark, some like broken stems or buds, and others even look like bird droppings.

While the importance of "not being seen" during the day can't be overstated, how does the White Underwing deal with nocturnal predators, like bats? As it happens, the White Underwing and most other members of the Family: Noctuidae, have evolved a pretty good trick for dealing with bats. First of all, they can hear the bats! Noctuid moth ears are attuned to the exact frequencies of sound that bats use for echo-location. Then, when they are flying about and hear a hunting bat, they start evasive maneuvers. The moth will fly downward in an erratic manner and seek a place to land and hide until the hunting bat moves off. Hey, every animal or plant species alive on earth today has something up its sleeves! The White Underwing has earned its continuing place on the tree of life.

Thanks for learning about the White Underwing Moth! Bye for now!

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More bug stuff in NatureNorth:

Giant Silk Moths | Silk Moths in the Classroom | Marvelous Monarchs

Acknowledgments

Some of the information presented in this article came from the following sources:

The Peterson Field Guide Series: A Field Guide to the Moths of Eastern North America. 1984. By. C. V. Covell, Jr. Houghton Mifflin Co., Boston.

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