At the back end of September 2011 we started to get the odd ladybird in the front room of our house climbing the curtains or across the light shade. From the outset I knew that this wasn’t one of our native species and was more likely to be the Harmonia axyridis (Harlequin Ladybird) which I had read about several years ago. Gradually more appeared over the next few weeks in nearly every room and we constantly kept putting them back outside rather than squashing them. After month they seemed to be everywhere, one morning I counted 68 in two rooms!
The windows on our property are the original wooden ones and unfortunately they aren’t a tight fit in places thus making it cold in the winter however perfect it appears for Ladybirds to squeeze into for the winter months. They mainly congregated in the groves behind the hinges at the top of the frames clambering on top of each other, it appears, to an optimum position for hibernation.
At first these new ‘pets’ proved a novel talking point and between the family and friends who visited as everybody loves a Ladybird, don’t they? However after 6 weeks we were fed up of putting them back outside hence a closer inspection of this alien invader was deemed necessary.
The harlequin ladybird was introduced to North America in 1988, where it is now the most widespread ladybird species on the continent. It has already invaded much of northwestern Europe, and arrived in Britain in summer 2004. It has spread across the country in just 4 years and is now one of the fastest spreading non-native insects in Europe and the most invasive ladybird on Earth.
Harmonia axyridis is a typical coccinellid beetle in shape and structure, being domed and having a smooth transition between its elytra (wing coverings), pronotum and head. It occurs in three main color forms: red or orange with black spots (known as form succinea); black with four red spots (form spectabilis); and black with two red spots (form conspicua). However, numerous intermediate and divergent forms have also been recorded. The Johnson is typically large (7-8 mm long) and even more dome-shaped than native European species (these characteristics distinguish H. axyridis from native species in the UK). It often has white markings (typically defining an “M”- or “W”-shaped black area) on its pronotum, and usually brown or reddish legs.
It hibernates in cooler months, though they will wake up and move around whenever the temperature reaches about 10 °C (50 °F). Because the beetles will use crevices and other cool, dry, confined spaces to hibernate, significant numbers may congregate inside walls if given a large enough opening.These beetles use pheromones to “call” each other, allowing for the large gatherings that are often seen in the Autumn.
They often congregate in sunlit areas because of the heat available, so even on fairly cold winter days, some of the hibernating beetles will “wake up” because of solar heating. These large populations can be problematic because they can form swarms and linger in an area for a long time. These beetles can form groups that tend to stay in upper corners of windows. This beetle has been also found to be attracted to dark screening material for its warmth. This beetle has good eyesight, and will come back from where it was removed, and is known to produce a small bite if provoked.
H. axyridis, like other lady beetles or ladybirds, uses isopropyl methoxy pyrazine as a defensive chemical to deter predation, but also contains this chemical in its hemolymph at much higher concentrations than many other such species. These insects will “reflex bleed” when agitated, releasing hemolymph from their legs. The liquid has a foul odor (similar to that of dead leaves) and can cause stains. Some people have allergic reactions, including allergic rhinoconjunctivitis when exposed to these beetles. Sometimes, the beetles will bite humans, presumably in an attempt to acquire salt, although many people feel a pricking sensation as a lady beetle walks across the skin. Bites normally do no more harm than cause irritation although a small number of people are allergic to bites.
Unfortunately for our native species these invaders are very effective aphid predators and have a wider food range and habitat than most other aphid predators (such as the 7-spot ladybird) and so easily out-compete them. They also do not have a requirement for a dormant period before they can reproduce, as some ladybirds have (e.g. 7-spot and eyed ladybirds), and so have a longer reproductive period than most other species. In 2004 in London, H. axyridis larvae were found still feeding in late October, long after all the native species had sought overwintering sites. When aphids are scarce, H. axyridis consume other prey including ladybird eggs, larvae and pupae, butterfly and moth eggs and caterpillars. They can disperse rapidly over long distances and so have the potential for rapid geographic expansion.
Numerous methods of control have been investigated in areas where this beetle has been introduced and causes a threat to native species and biodiversity and to the grape industry. A consideration in their control is the fact that when the beetles die they release a chemical that attracts more beetles. Methods of control include insecticides, trapping, removal of aggregates of beetles and mechanically preventing entry to buildings. Methods under development involve the investigation of natural parasites and pathogens, including the use of parasitic sexually transmitted mites and fungal diseases.
H. axyridis traps are available that contain the pheromones used by the beetles to attract each other into large gatherings. The best methods for dealing with them in private homes involve sealing openings they may enter. Sweeping and vacuuming are considered effective methods for removing them from homes though this should be done carefully so as not to trigger the defensive reaction known as reflex bleeding. A nylon stocking placed inside the vacuum cleaner’s hose, secured with a rubber band, allows the beetles to be “bagged” rather than collecting inside the machine. A trap designed for indoor use was developed which attracts the beetles with a light and seals them in a removable bag.
We have decided to go for the DIY control method of specially adapting our hoover with some old tights and have removed all of the visible insects from each room and disposed of them at the bottom of the garden. Time will tell if we have effectively dealt with the problem or merely delayed 2012 autumn invasion!