Insect in the spotlight: Rosemary Beetle

A week ago on Friday, I came home from work and noticed this shiny beetle, sitting on lavender. Since I had never seen a beetle like this before in the Netherlands (most beetles here are brown/black/grey and definitely not shiny), I had to make some pictures and look up which species it was.

chrysolina americana

Because of my job at the entomology department, I had a feeling it might be a member of the leaf beetles family (Chrysomelidae) because of its shine. So being the good biologist that I am, I entered this name into Google Images and kept scrolling until I found ‘my’ beetle. It appeared to be the Rosemary beetle (Chrysolina americana). I was right in thinking that it was odd to see this species in my country, because it is considered an invasive species from the east and south of Europe. It is in the last two decades that they spread out to the rest of Europe.

Partly why this beetle caught my eye was also because it was sitting in the lavender bush. Normally I don’t see that many insects, let alone beetles on this particular plant, but apparently the Rosemary beetle loves lavender. It seems a bit odd in combination with the name, but these beetles feed on plants of a particular family called Lamiaceae, which includes lavender, thyme and rosemary; the latter being their favourite. Unfortunately for it though, there are no rosemary plants in my garden, so it had to settle for the next best option.

The host plants are not only being used for food and shelter, but also for defense. I’m not sure whether this is also the case for the Rosemary beetle, but other leaf beetles use toxic substances from the plants they live on and secrete it whenever they are disturbed. Because they love to eat these plants and use it as a host, this species is considered a pest. So far, I’ve only seen one, but I am checking regularly if it comes back with more friends. However, I do not think it would come to that, since this species has very short wings and can barely fly. It is amazing though that despite this, this particular specimen has found its way to the only lavender bush in my garden.


— I have decided to change the name of the Insect of the month posts, since I felt that the name did not fit the frequency in which I post. There are times when I will probably not post for a month, but this summer season I have a feeling that I will be coming across various insects, in the garden or at my job, so I will try to post more insects. I hope you’ll appreciate the name change and as always you’re welcome to leave a comment or question! —


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