Question Time

-• tzon

In response to a number of interesting

questions which were put to us by keen visitors to the Suffolk Show we thought that a 'Questions and Answers' spot might usefully become a regular part of this magazine. To start us off, here are three Questions that were put to us which will hopefully be of interest to all our readers.

QI. What exactly is a tetrad and why is su~h a measurement used to record butterfly sightings?

A. Let's go back to square one so to speak and briefly review the National Grid system with which we should all at least be familiar due to the excellent series of 1:50,000 Ordnance Survey maps( those with the magenta covers!). The

National Grid system is broken down into squares which get progressively smaller. They begin with 500km squares (identified by single letters} which are then divided into I 00 km squares (identified by the 500 km square ktter plus a farther letter of the alphabet, excluding T). In Suffolk for example, we are mainly concerned with TL and TM with which map references are prefixed. The sides of each I 00km square are then subdivided into 100 points I km apart, measured .from the south-west corner of the square eastwards (eastings) and northwards (northing,). The parallel grid lines joining these points and marking out 10,000 squares of 1km sides are familiarly numbered on the map margin which we use to identify a particu/,ar point. Blocks of four I km squares represent a tetrad (2km x 2km cover the same area).

National atlases often disp'4y recording units of I 0km squares which contain 25 tetrads (5 across and 5 down). Regional atlases such as Mendel and Piotrowski (I 986) The Butterflies of Suffolk, The Suffolk Naturalists' Society, are usually plotted by tetrads but with the actual data gathered by I km squares. The records for The Millennium Project will be formu'4ted in a simi'4r way, national recording by I 0km squares but with Suffolk recording by 2km squares.

Q2. What are the black and red butterflies we have been seeing?

We cannot find any descriptions in our butterfly book.

A. Interestingly, more than one person took the time to describe their observations.

It_soon occu"ed to us that the descriptions were either that of Cinnabar or Burnet moths.

From the descriptions and the fact that we were being told that these sightings had occurred during the previous two weeks i.e. the last two weeks of May, it

seemed certain that the Cinnabar moth (Tyria jacobaeae) was the insect concerned. The flight period of this moth begins in }.1ay compared to June for the Five-spot Burnet (Zygaena trifollii). Although the Cinnabar has two scarlet spots along the outer margin of each wing, the 'clincher' is the long scarlet stripe along the leading edge of the wing.

Fortunately, they are common in Suffolk and fly from May to July in one generation and although not strictly a day-flying moth, they are readily disturbed from low hrrbage by day. Most people will. be familiar with the yellow-and-black banded caterpillars which feed gregariously and conspicuously on ragwort without fear of predators due to their highly distastefal nature. Cinnabar moths are very attractive insects. Who says moths are colourless night flyers?

Q3. When should I visit a site to cover the main flight periods of all its butterflies?

A. Four times at least in a year:

Early May

Mid-June

Mid-July

Late August

It is also worth mentioning the following; the importance of air temperature and time of day.

Air Temperature. If this is greater than I 7C many species will fly even if there is no fall sun. Below I 7C it will only be worthwhile visiting during sunshine. But even on a sunny day, if the temperature is below 13C expect only a few sightings. Also, few sightings are likely in windy weather. It is worth noting that on dry, hot days, butterflies may disappear to shade around midday to avoid dessication.

Time of Day. Butterflies get up late and go to roost early. Even in high summer it is often approaching 8.30 am before they will fly and by 630 pm, the majority will have disappeared. Exceptions are Purpv Hairstreak (Quercusia quercus) when in fact these are good times to ser. them. Painted Lady (Cynthia cardui) will also fly late and on good days, odd ones may be seen up to 8.3019.00 pm. During September to June, there are usually few butterfly sightings of any kind before around 10.30 am or after 4.00 pm.

Morning, providing it is warm and sunny, is probably the.)mt time for observation when butterflies are busy feeding after their overnight rest. A particularly good time is when the sun eventually breaks th;ough after_ a wet or dull start to the day. •

If you would like 'Question Time' to continue, please make sure that you send in your questions fo the editor before the end of the year and we will do our best to , provide answers in the next Suffolk Argus.