Longitarsus dorsalis (Fabricius), a nationally Notable beetle, is one of over 40 species of Longitarsus which occur in this country. All species are small (dorsalis is 1.5–2 mm) and jump like fleas using specially developed hind legs – hence their common name of Flea Beetles. Adults of L. dorsalis feed on the leaves of Common Ragwort (Senecio jacobae L.) and Groundsel (Senecio vulgaris L.) whilst their larvae feed on the roots. The species overwinters as an adult, hibernating in the soil, litter etc. around the foodplant. The beetle is not uncommon where I live and singletons sometimes occur in warm weather on the white wall of my bungalow but I have never seen them in any numbers.

On February 2nd 2007 I counted twenty specimens on the white wall of my bungalow and conservatory here at Brantham. More careful searching would, I feel sure, have revealed more. As far as I could see, no other beetle species were present. The walls and conservatory do not have bare soil abutting them and are either concreted up to the base (my driveway) or have a deep, 14 mm wide border of shingle bordered by paving slabs. Both foodplants occur commonly in the area and in my garden they are treated as weeds, with young plants being removed as soon as observed. This indicates clearly that the beetles had actually flown to the white surfaces rather than just having emerged from hibernation in soil at their base. A possible explanation for this activity may be arrived at if we examine temperatures in my area at the time. On the last day of January, the day temperature had been around 4.8°C; on February 1st the day temperature was about 7.4 °C. This sudden increase in day temperature had probably activated the beetles, stimulating them into flight. On February 2nd when I observed them actively crawling on my bungalow, they had probably arrived during the previous day but I had not noticed them. Day temperatures on the 2nd hovered around freezing and the beetles subsequently disappeared, presumably once again seeking out hibernation sites. Three days later, on February 5th, in a field not far distant, I found basal rosettes of S. jacobae peppered with holes which, from their size, I attributed to recent feeding by a Longitarsus species, although they could have been made by another Senecio-feeding member of the genus and not necessarily dorsalis. It, nevertheless, indicated extensive feeding activity at, in my experience, an unexpectedly early time.

No flea beetles could be seen, which was not surprising since day temperatures since the 2nd had hovered around freezing and night temperatures had been around -8°C on the nights of the 2nd and 3rd, and - 4°C the previous night. On February 11th, on a mild, sunny afternoon following significant snowfall three days earlier followed by heavy downpours, I noticed over a dozen L. dorsalis on the bungalow wall beside the drive. Walking to the field with the Ragwort damage noted one week earlier, I found the beetle in numbers on it, as well as floating in nearby puddles.

Hibernating beetles capable of flight used to be expected to do so with the onset of the first warm days of March and April. The activity described here was almost certainly another example of the kind of changes we are seeing more frequently as animals and plants adjust to our changing climate.

I am sure many other members have similar observations which they could share with us concerning the response of species to the changing pattern of our seasons. I hope this note may stimulate them to do so.