Mikes Nature Notes
Summer insect life
Whilst casting a glance at my bed of nasturtiums' the other
day I noticed the huge number of caterpillars of the Large white, or
'cabbage white', butterfly busily munching their way through the leaves. I
thought nothing of this until several days later when I saw them climbing
the walls on route to finding shelter in the eaves to build their cocoons.
However all was not well - surrounding many of them were clusters of bright
yellow blobs. On reading up on this phenomenon I discovered the ghastly
goings-on! They had been killed by an ichneumon fly, a type of parasitic
wasp which commonly attacks caterpillars, often wiping out up to 80% of a
The female wasp injects up to 150 eggs into the young caterpillar which has no means of defence. Using its body as a host the grubs grow inside and feed on the body tissue, eventually emerging to form their bright yellow cocoons. The host rapidly dies of course.
This is common and widespread behaviour for many species of wasp, each having remarkable and grisly methods of nurturing their offspring! The potters wasp (one for Tim!) makes a 'pot' from sand and saliva before sealing in a paralysed caterpillar with an egg. There is a mason wasp which makes tunnels in loose mortar to stash its prey. There is one that detects the tunnel of the alder wood wasp through the bark of a tree and bores a hole to inject eggs into a larva, however when this egg develops it is likely to be parasitized by another wasp species
a (hyperparasite) in turn! Amazing stuff - you can't turn your back if you're an insect!
We have been surveying butterflies along the Valency Valley once again this summer. This year has been a good year for butterflies, and we have recorded the rare pearl and small pearl-bordered fritillaries once more. There is a healthy population of the more widespread silver washed fritillary which is probably the largest British species and can't be missed despite its rapid flight.
Both here and on the cliffs I have noticed large numbers of the clouded yellow butterfly this year (dark yellow with black wing tips). This is a migrant summer species from southern Europe and as such numbers fluctuate from year to year. In its warm native countries this strong, fast flyer is a prolific breeder producing up to four broods a year. Occasionally there is a big influx into Britain when the European population has swollen in favourable conditions. Eggs are laid in great numbers on clover, lucerne and trefoils.
Spring migrants will have time to breed in the UK producing a single brood in the autumn, but none can survive the cold damp November weather.
Moths are perceived as the rather dull cousins of butterflies but when you look into them they are equally fascinating. They are part of the family of insects called Lepidoptera as are butterflies. This is a Latin word literally meaning 'tile-winged' - obviously a reference to the scales on the wings. There are about 2500 species recorded in the UK, but only 900 or so of these are the more commonly studied macro moths which are larger and more easily identifiable. The rest are micro moths and are just impossible!
The main difference between moths and butterflies anatomically is the shape of antennae. Butterflies have 'clubbed' antenna, moths, in the main, do not. Moths, of course, mostly fly by night and rest in the day. There are several day fliers - the brightly coloured cinnabar and burnets, the garden tiger and the humming bird moth are all examples which are prolific towards the end of summer.
The moth lifecycle is the same as butterflies, but typically adults do not live as long. Interestingly, though, there are a few species that do not feed as adults and have no developed mouth parts - their short adult life is sustained purely from the stored fats and carbohydrates gained as a feeding larva.
The commonest way of studying moths is to set up a light trap overnight, which allows you to identify them the following day. You need a special bulb - one that emits partly UV light called a mercury vapour bulb to work best. Apparently, the reason moths so readily come to light is linked to the moon
Ever since the flood, we have been keeping a watchful eye on the appearance of invasive plants along the valleys. We all know about Japanese knotweed, and this hasn't emerged as a problem. What have' turned up though, especially this summer, are large large quantities of Himalayan Balsam.
This garden escape has found its way into the Valency catchment, and has begun to spring up all over the place. It spreads prolifically and can soon take over an area, much like knotweed. It is a tall very fleshy stemmed plant that likes stream sides and damp grassland. It has a very ornate pink flower and the ability to fling its seed a great distance once the ripened seed pods explode - some of you may have seen this filmed on BBC Wildlife shows!
Because of this we have been pulling up the plant whenever we see it in the Valley before this occurs! I have seen whole fields of the stuff when out walking in other parts of the country, where it's obviously not been managed, so would hate it to get out of control here.
Information by kind permission of The National Trust