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Ladybirds are becoming much more active now as the weather warms up and their favourite food source - aphids become more widely available (but hopefully not on my vegetable patch).

May is the main breeding season for ladybirds so you can expect to see a lot more of our 51 resident species (only 29 of these are recognisably ladybirds) out and about over the next month.

Among our resident species you'll also spot the increasingly common, invasive harlequin ladybird which is being carefully monitored.

Confusingly it comes in many colours, many of which resemble our native ladybirds making it difficult to distinguish.

Introduced to north America and mainland Europe as a biological control for aphids, their ferocious appetite has led to the decline of our native species.

Not only do they eat aphids, they will also eat ladybird larvae and other insect larva such as butterfly eggs, caterpillars and lacewing larvae and at least 1000 British insects are now at risk.

First spotted in the south east of England in 2004 they have expanded rapidly, north and west.

Harlequin ladybird in Llangollen by Keith Evans

Here are a few simple ways to distinguish harlequin ladybirds from resident species from the :

• If it's less than 5 mm (1/5 inch) in length, it is definitely not a harlequin ladybird.

• If it's red with precisely 7 black spots, it is a 7-spot ladybird.

• If it has white or cream spots, it is a striped ladybird, an orange ladybird or a cream-spot adybird.

• If it is large, burgundy coloured and has 15 black spots, it is an eyed ladybird .

• If it has an orange pronotum, and fine hairs all over the elytra, it is a bryony ladybird..

• If it is black with four or six red spots, two of which are right at the front of the outside margin of the elytra, it is a melanic form of the 2-spot ladybird..

A recent led by Dr Helen Roy from the UK's Centre for Ecology & Hydrology and Tim Adriaens from the Research Institute for Nature and Forest (INBO) in Belgium has found that seven resident species are at risk.

The seven species in decline are the 2-spot, 10-spot, cream-spot, pine, orange, 14-spot and 22-spot ladybirds.

Find out more about Harlequin ladybirds on 91Èȱ¬ Nature.