Sunday, May 28, 2017

Spring Visitors: Ladybug Beetles

ladybugAmong the many groups of insects that exist on our planet, the most abundant, diverse and ecologically successful are the beetles. And while many of these hard-shelled bugs are viewed as ugly and unwanted by humans, the ladybug beetle is considered to be one of the most attractive and environmentally friendly creatures in nature.

With a conspicuous dome-shaped, orange shell marked with black spots, the ladybug is difficult to mistake for any other invertebrate. Like all insects, there are numerous species of ladybugs that reside in our region, and the subtle differences in the color and pattern of its markings is the common means of distinguishing among the members of this insect group.

The 9-spotted ladybug (Coccinella novemnotata) is the species that holds the greatest notoriety in the Northeast. Because of its brightly colored appearance, benefit to those individuals raising crops or garden plants in the State, and its former abundance throughout the region, it was selected as New York’s official State insect. As its name implies, this ladybug has 9 spots on its back with 4 of these round black marks on each of its sides and one directly in the middle of its back, close to its upper thorax, known as the pronotum. (The pronotum is a small and separate shell-like plate that appears like shoulder pads, or a collar, immediately behind a beetle’s head.) Additionally, the pronotum of this species has conspicuous white markings on both its right and left ends and a front edge that supports a white stripe.

The 9-spotted ladybug population began to decline throughout the Northeast during the 60’s and 70’s until it was considered to be extirpated from our State by the late 80’s. Just last summer, however, a small number of these ladybugs were observed toward the end of Long Island. It is unknown how extensive a population there currently may be in that area, or if there are any other localized clusters that have reestablished themselves elsewhere in the State. It is unfortunate that the insect chosen to symbolize New York is no longer a part of our fauna; however, it may be that this bug will stage a comeback, just as the bluebird has done.

Presently, the most common species of ladybug in this region is one that was introduced into North America from Asia. Simply known as the Asian ladybug (Harmonia axyridis), this beetle is similar in size, shape and color to the 9-spotted ladybug, except that it has more than 9 spots on its back and sides. A black m-shaped splotch that appears on its pronotum is the feature that is used to identify this ladybug.

Like other ladybugs, the Asian ladybug has a voracious appetite for the tiny plant pests, like aphids, that cause harm to many forms of vegetation. Also, this species overwinters as an adult and seeks out warm places in autumn, where it clusters with other individuals to pass this cold season. Once one individual locates a favorable shelter, like an entrance to an attic, a crack behind a chimney, or a gap between the siding of a house and a window, it will emit a special chemical that attracts other Asian ladybugs in the immediate vicinity. As each individual discovers the shelter and elects to pass the winter in its confines, additional scent used to announce the location of a winter retreat is produced. As the amount of this chemical increases, ladybugs from greater distances are able to detect this fragrance, which increases the number of individuals that congregate at that site.

The Asian ladybug becomes dormant when the temperature drops to near 50 degrees. A sun-baked, south-facing wall can frequently rise to this temperature even when the air is only in the upper 30’s. The ability of this insect to squeeze through small openings often enables it to gain access to the inside of homes once it has taken up residence in an attic, beneath a window, or around the siding next to a door. During sunny days in spring, these bugs frequently emerge from their low temperature induced state of dormancy, and may find their way inside your house. Because of their massive numbers in such locations, the Asian ladybug is considered to be a nuisance by those people plagued with massive numbers swarming around sunlit windows.

When confronted with ladybugs this season, it is best to attempt to identify the species. The Asian ladybug is considered to be an invasive species, however, one supporting 9 spots is our official State insect, and its presence should be reported as soon as possible to the DEC.

Photo: Ladybug, courtesy Gilles San Martin.

A version of this story first appeared on the Adirondack Almanack in 2012.

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Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.

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