September 2016

Evolution needs three factors – a means of reproduction, a method for change, and a struggle for life.  Remove any one of these factors, and evolution stops.  Remove the ‘struggle for life’ and you end up with species like the horseshoe crab that have no effective predators or parasites and have stayed the same for millions of years.  Quite often though, the struggle for life ends up as a sort of arms race between predator and prey, as one evolves an effective defence and the other gets round it.  Nothing exemplifies this better than the humble caterpillar.

The role of caterpillars is to eat.  Their purpose is to put on as much weight as possible because adult moths and butterflies don’t need or have the ability to eat any protein, they can only top up their energy reserves with nectar while looking for the chance to put into practice the ‘means of reproduction’.  Of course the fatter and juicier they get, the more attractive caterpillars are to predators like birds that need to feed their growing brood.  The first defence is to hide, which many species do quite effectively by burrowing into stems, under bark, or underground.  But this limits their food supply and stops them getting at most of the nutrients concentrated in the leaves of plants.  So an effective way of eating leaves without being eaten is to look like a leaf, or failing that to look like a twig.  I have long marvelled at the camouflage displayed by adult moths that appear to look like lichens or tree bark, or even broken birch twigs (buff-tip moth), but caterpillars take an equally bizarre range of colours and forms. 

Buff-tip Moth - or Birch twig

Another path that evolution has taken is to make some caterpillars unpalatable.  One of the ways this manifests itself is in the hairiness of some caterpillars.  A fine example of this is the woolly bear, the caterpillar of the garden tiger moth. 

Garden Tiger moth caterpillar - Woolly Bear

Whilst eating something hairy may be unpalatable, if the hairs themselves contain irritating chemicals, then so much the better.  One caterpillar that has such hairs is that of the brown-tail moth.  So irritating are those hairs that they can even penetrate human skin and cause rashes.  A young bird may not have come across a brown-tail caterpillar before and so the caterpillar gets eaten, or partially eaten, but part of the species success is due to the two bright orange dots on its back.  The bird may forget the hairs but the warning dots make a powerful and obvious reminder.

Brown-tail moth caterpillar

If you have fuchsia in your garden, you may well find a bright green caterpillar with what looks like large eyes near its head.  It can retract its head, which puffs out its body and displays the large eyes to warn off any potential predator.  As the caterpillar gets bigger and the leaves get eaten, the body fades to a dark grey colour, which with the mobile and retractable head gives the moth its name – the elephant hawkmoth.  If you don’t have fuchsia, then another favourite plant is rose-bay willow-herb.

In this discussion about prey and predators, I am forgetting the prey of the caterpillar – the plants that they prey upon.  Evolution has equipped these plants too with some remarkable defences.  They are not able to hide, but they do thorny and unpalatable quite well.  One plant, ragwort, is so poisonous that it reputedly kills horses and cattle, though not if their owners look after them properly (whether or not they have ragwort growing in their pastures).   If you have ragwort, you may see a very conspicuous caterpillar on it with striking black and orange stripes.  This is the cinnabar moth caterpillar which is immune to the poison, but will happily pass it on to any predator that ignores the bright warning stripes.

Elephant Hawkmoth caterpillar showing its 'eyes'

Do you know the really amazing thing about a caterpillar turning into a butterfly?  They both have the same DNA – what sort of a blueprint is that?

Cinnabar moth caterpillar on Ragwort

And just for reference, here are photos of the adult moths to show just how adaptable their DNA is.

Cinnabar Moth

Brown-tail moth

Garden Tiger moth

Elephant Hawkmoth

August 2016

If you were to drive (or walk) down Denge Marsh Road in Lydd, you would end up on a rutted track that takes you right down to the sea, not far from Dungeness Power Station.  In fact, the track runs between the power station and Lydd Firing Ranges.  As you may expect, it is a bleak and inhospitable place which is exactly the sort of place to find some of the best nature.  The flora there is unusual because the place is unusual, though much of it is familiar if you have spent any time around Rye Harbour or at the Dungeness RSPB reserve.  There are the usual shingle species like viper’s bugloss, sea beet and sea kale, and some that seem to turn up almost anywhere like scarlet pimpernel, woody nightshade, and rest harrow.

Recently however, I came across a species that I’d never seen before.  It was a very tiny plant with a low growing prostrate habit with evergreen, succulent-like leaves.  It had carpeted a large patch of ground and could easily have been overlooked and mistaken for moss.  There was a redness to it that made me look twice and it turned out to have what appeared to be bright red buds. 

Sea-heath - Frankenia laevis - with rabbit dropping for scale

Sea-heath - Frankenia laevis

Identification for me nowadays, consists of taking plenty of photos (assuming the subject stays around for long enough, which most plants do well), and then comparing them with the field guides when I get home.  So I did this with my mystery plant and chose a plant that looked the closest match, which turned out to be sea-milkwort.  Of course, to be certain it is best to get the photos looked at by an expert.  Though I know a couple of very experienced botanists I could ask, I decided that I may get a quicker answer on Facebook.

Now I know that sounds unlikely, but Facebook has grown up.  I know that a lot of people in the village use Facebook – it’s a good way to keep up with the grandkids, after all, but recently Facebook added a feature called Facebook Groups.  Groups are a way of letting like-minded people get together and share ideas and photos, and the wildlife and nature community has leapt on this as a way of helping each other identify things and to show each other what they’ve seen (as well as having the serious purpose of encouraging people to formally record their sightings).  There are groups for birds, beetles, insects, bees, wasps and ants, you name it, there’s a group for it.  I belong to the Wild Flowers of Britain group, amongst others, and so I posted the photos on there.  My suggestion of sea-milkwort didn’t last long.  The first alternative suggestion was mossy stonecrop, but this was also rejected in favour of sea-heath – Frankenia laevis.  When I looked this up, it turned out to be a rare plant that also had pale mauve flowers, which didn’t seem to fit with what I thought were bright red flower buds.  All of the Facebook groups are moderated by experts or at least enthusiastic and knowledgeable amateurs, so could they have got it wrong?

Sea-heath - Frankenia laevis

Well today, I went back to see if any of the red ‘buds’ had opened.  None of them had, and on closer inspection, they weren’t flower buds but leaves that had turned red.  I was disappointed and as I was about to leave I spotted some pale mauve flowers in a small corner of the patch, and sure enough they were attached to branches having both green and red leaves.  Sea-heath indeed.  The fingerprints on my index finger at the bottom give some idea of the size of this plant.