The Ladybird invasion-What you need to know

People of Britain, have you noticed ‘swarms of ladybirds this year? Do you have masses of these red and black beetles on your house…even coming inside uninvited? You are not alone. It sounds like you’ve got Harlequin ladybirds. This article should provide you with everything you need to know about these alien invaders and what to do about them, as well as help to dispel some of the myths about them which have been promoted by the media.

1. What is a Harlequin ladybird?

The Harlequin ladybird (scientific name Harmonia axyridis) is an invasive non-native species of ladybird, originally from Asia.  Harlequins arrived in the UK in 2004 after crossing the channel from mainland Europe, where they were introduced to control plant pests such as aphids and scale insects. They have now spread across the UK from Essex, east to Northern Ireland and north to the Shetlands. They are an environmental concern in the UK, since they appear to be causing drastic declines in some of our native ladybird species by competing with them for food, eating their young and spreading infection.

You may have heard that Harlequin ladybirds are mostly black. In fact, Harlequins come in a variety of colours and patterns. Whilst they are often black with 2 or 4 red blotches, they are usually  red/orange with 0 to 21 black spots. Their common name refers to these varied colours.  Thus if you see gatherings of multi-coloured ladybirds they are most likely all Harlequins. Here are a few features you

The many colour forms of Harlequin ladybirds (c) entomart.

The many colour forms of Harlequin ladybirds (c) entomart.

can use to positively identify Harlequin ladybirds:

  • They are larger than most of our native ladybirds at 5-8 mm long
  • Their legs are brown (our native ladybirds of similar size have black legs).
  • Colour forms with red/orange wing cases tend to have a black ‘M’ mark
    on their thorax (mid-section)

 

2. Why am I seeing so many?

Gatherings of Harlequins at this time of year are completely natural for this species. They are gathering together to find a sheltered spot to hibernate over the winter. A common name for them in America (where it has also been introduced) is ‘Halloween ladybirds’ because they become more noticeable from late October. Harlequin ladybirds have a particular fondness for houses and outbuildings as cosy hibernation sites, and have a habit of clustering in groups of up to tens of thousands of individuals in corners. They are also attracted to sunny, south-facing walls and fences in search of warm,  sheltered crevices.

Though this is an annual phenomenon, there do seem to be more Harlequins around this year. This is possibly due to the milder autumn which could have extended their breeding season, boosting their population.

A winter aggregation of Harlequin ladybirds (c) Gilles San Martin (CC.BY.SA 2.0)

A winter aggregation of Harlequin ladybirds (c) Gilles San Martin (CC.BY.SA 2.0)

3. Should I be worried about them?

A mass influx of ladybirds into your home can be alarming but don’t panic..they’re mostly harmless, at least to people. The ladybirds are only coming indoors to sleep through the winter. They are not looking to feed or breed and pose no threat to human health unless eaten in large amounts. Citizens are thus advised to please refrain from eating ladybirds, no matter how delicious they may appear. Like other ladybirds, Harlequins excrete mild defensive toxins if threatened, but they are fine to handle.  There are occasional cases of dogs consuming numbers of Harlequin ladybirds, which get stuck in the mouth where the toxins can cause excessive salivating and mouth burns. In the unlikely event that your dog is affected, it can be cured simply by removing the ladybirds. The foul warning smell given off by Harlequin ladybirds when stressed is usually enough to deter predators, including dogs.

Other effects in the house are minor, such as small yellow stains, the odd dead ladybirds and the slight chemical smell. However, it is best not to leave ladybirds in the house (see 4.).

You may have heard that Harlequin ladybirds carry sexually transmitted infections (STI’s).  In fact, the STI they carry only infects ladybirds. The disease is an infection with the fungus Hesperomyces virescens which causes fungal growths on the ladybird’s exoskeleton known as Laboulbeniales disease.  Despite media claims, this disease did not arrive in the UK with the Harlequins but was already present on our native ladybirds, and does not kill either of them.
However, Harlequin ladybirds do carry a parasite in their blood-known as a microsporidian- which is harmless to them, but fatal to some of our native ladybirds, such as the 2-spot ladybird (Adalia bipunctata).  The parasite may be transferred when native ladybirds eat the eggs or larvae of Harlequins. This may be a reason for the decline of native ladybirds since Harlequins invaded.

 

4. What should I do about them?

As a non-native species damaging to our native wildlife, it may be tempting to destroy Harlequin ladybirds. However experts agree that Harlequins are now so abundant, widespread and fast-breeding in the UK that killing any you see will have no impact on their numbers in the long term.  Moreover, unlike many non-native species resident  in the wild in Britain such as Grey squirrels and Signal crayfish,  it is not illegal to release Harlequin ladybirds into the wild under UK law, so it is fine to put them back outside. Note that spraying pesticides in your property is more harmful to your health than ladybirds would be.

Even if you don’t mind sharing your home with Harlequins, the house is not the best place for them to hibernate. Central heating will cause them to wake up and move about, using up their fat reserves so that they may die of exhaustion. Hibernating ladybirds also need a degree of humidity and houses tend to be too dry, so they can become dehydrated. It is best to relocate them outside to find a more suitable hibernation spot or in an outbuilding with an easy escape, which provides them with a cooler and more humid refuge.

Remove ladybirds you have found manually. You can use a glass and card (as with spiders) for individual ladybirds, or a dustpan and brush works well for removing clusters. For ladybirds clustering in high places, use a vacuum cleaner with a stocking or tights stretched over the tube where it connects to the hose, then empty them out immediately in a new location.

There are no known deterrents for Harlequin ladybirds. The best way to prevent them from coming into your house is to find the gaps or cracks when they are entering and seal them with silicone (so long as this does not restrict your property’s ventilation).

 

How can I help the situation?

There is currently no known way to control Harlequin ladybirds without also killing our 46 native ladybird species. However, studying the spread of the Harlequin ladybirds can provide important information to research the biology of invasive species. You can contribute to this by submitting your sightings of Harlequins (and all other ladybird species) to the UK Ladybird Survey.

 

For more information on Harlequin ladybirds see the links below:

Buglife-Harlequin ladybird

GB Non-Native Species Secretariat-Harlequin ladybird

Harlequin ladybirds in the Guardian

UK ladybird survey

Ladybuglady.com- Ladybug home infestations (an American site)

Hesperomyces virescens

Microsporidian parasite

Harlequin ladybirds and dogs

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RoryD

RoryD

Conservation Ecology graduate with a particular interest in entomology. Pleased to be a volunteer and subcontractor with Buglife. Views and fixations are my own.

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