Thursday, 17 November 2005

A four-spotted two-spot

We had a visitor to our office this week, quite possibly attracted by the lights that illuminate our work on these increasingly dark afternoons. The visitor in question was a ladybird, a two-spotted ladybird to be precise. This species is one of our most familiar ladybirds, easily recognised and seemingly as at home in urban areas as it is in the wider countryside. Two-spotted ladybirds often bring themselves to our attention through their habit of hibernating around our homes, even appearing indoors during spring. They are good creatures to have around if, like me, you are a bit of a gardener. Two-spotted ladybirds have a real taste for aphids, feeding on a range of different species including the black ones that are associated with leaf curl on cherry trees.

I should not have been surprised, therefore, to encounter one inside at this time of year. What did cause me to raise an eyebrow though was the fact that this particular individual was of the melanic form. In melanic individuals, the red and black colouration is reversed. So, instead of black spots on a red background there were red spots on a black background. Not only this, but instead of the two spots that give this species its name there were four! (It is worth mentioning that some melanic forms of this species have six red spots.) One of the surprising features of ladybirds is just how much variation in colour and pattern there may be within a species. While some species are pretty uniform in their appearance, others are very variable and the two-spotted ladybird is one of the most variable of all. The most common form of two-spotted ladybird is the one with a large black spot, set against a red background, on each wingcase. The melanic form is far less common. One recent study suggested that within a population about 4% of individuals would be melanic. Because this variability in colour and pattern has a genetic basis, you sometimes find clusters of a particular colour form within a small area. However, this was the first such individual I had encountered locally. One of the problems, for a budding entomologist at least, with having such variability is that it can make it more difficult to identify a particular species. The individual I had found was superficially similar to a pine ladybird but lacked the characteristic turned up edges to its wingcases shown by the latter species. I did take the ladybird home though, to double-check my initial identification with a hand lens. Seemingly underwhelmed by the amount of attention it attracted, the ladybird was released by my shed in the hope that it would find a safe place to spend the winter.

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