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Adalia bipunctata, Two-Spotted Lady Beetle

Adalia bipunctata, the two-spotted lady beetle (or two-spot), has quite a wide range. It is native to both North America and Europe, and can still be found throughout both. It is actually still very common in western Europe. However, even though is not currently listed as endangered or threatened, its range in North America seems to be narrowing. Our greatest fear is that it’s declining along with Coccinella novemnotata (C-9, the nine-spotted lady beetle) because of the same factors, and that it, too will soon disappear from large areas of its former range.

The two-spot is one of about 450 lady beetles (Coccinellidae) that occur in the US. It is one of the more recognizable species, with adults being dome shaped and about 4-5mm long. Typically, its pronotum is black and white and its abdomen is orange-red with 2 prominent black spots, one on each elytra (hence its name). However, there is a melanic polymorphism in the two-spot, and there also exists a black form with four or six red spots on it, and other intermediate, rare forms. Larvae are grayish black with yellow and white markings, and look a lot like tiny alligators. They emerge in early to mid-spring, and take a little less than a month to mature into adults, then live for 1 or 2 years.

The diet of larval and adult two-spots is the same. They are carnivorous and eat soft-bodied insects. The two-spot’s main prey item is aphids, though they will also eat other soft-bodied hemipterans such as scale insects and mealybugs. They also feed on mites and insect eggs, and will resort to cannibalism as well. Thus, two-spots are valuable to us because their prey are detrimental, feeding on our agricultural crops. Lady beetles are one of the most publicly recognized and revered insects, so they also help with conservation. Endangered or threatened lady beetles are flagship species - people want to save them because they like them, and so other organisms in their environment will be protected, too.

The two-spot can be found in a variety of habitat - meadows, fields, gardens, forests, etc. They will live in nearly any vegetation so long as there is a food source. So why might they be declining? We have a few ideas. Land is being converted from agricultural use to forested areas, which may have caused a decline in the two-spot’s prey, or made it harder for females to find prey aggregations, thus lowering the number of oviposition sites. As with C-9, two-spots may be declining due to other species of lady beetles living in their range and either cannibalizing them or using up their resources. As several studies suggest, poor prey quality can lower prey searching behavior and fecundity. Parasites, parasitoids, pathogens, increased cannibalism, use of insecticides and transgenic crops, and hybridization with other species may also be lowering the two-spot’s population density in certain areas.

The number one way to help the two-spot, as is often the case, is to gain more information about its condition and spread this knowledge publicly. Before we can try to ensure that this species does not disappear from its range, we must find out exactly why it is declining. So, we should look into the above listed possibilities for decline, and either rule them out or prove them to be occurring. Using “citizen science” can help; a national survey done by regular citizens can amass invaluable data. Conservation efforts are in their beginning stages, and we will hopefully learn what is affecting this lovely insect’s populations before its range does shrink drastically.


Written by: Danielle Martinez , 2006

Image credit: NA