Tuesday, 26 June 2012
We have been watching a group of very colourful caterpillars in the garden over the last few days. Many of you will recognise these caterpillars from the image, but perhaps have wondered what species it is and whether the adult is equally visually stunning. A strong clue to the caterpillars identity is its favourite food plant, Mullein, and hence its name the Mullein Moth (Shargacucullia verbasci). Our particular caterpillars featured are feeding on Great Mullein (Verbascum Thapsus) with its distinctive velvety elephant ear-like leaves - or what’s left of them. This moth will also feed on other Verbascum species, but also Figwort (which I have more frequently observed) and Buddleia.
The caterpillars seem unconcerned with their high visibility ‘jackets’, almost advertising their bright yellow and black markings – this is presumably to warn any predators not to eat them because they taste bad. This stunning colouration is in stark contrast to the adult moth form which at rest appears to mimic a dead plant stalk.
Many gardeners are all too acutely aware of how prone their Verbascums are to attack by the caterpillar of the Mullein Moth, which can consume much of a plant's entire foliage in a day. I counted only about three caterpillars on our Great Mullein and today we are left with little more than a stump. However this is where their colouration works against them as they are easy pickings for green-fingered predators!
Tuesday, 5 June 2012
A few weeks ago I was lucky enough to spot a Grass snake (Natrix natrix) crossing our local country lane. I managed to grab it momentarily to get a good look before releasing it into the hedge. Then last week during the warmer weather I spotted another much smaller snake-like animal, a Slow worm (Anguis fragilis)- the Anguis is taken from the Latin, 'slim' and 'snake'. However, as many of you will know it is not a snake, but a legless lizard, being distinguishable by its closable eyelids which is why it is also called the Blind-worm – snakes do not have any eyelids.This particular specimen was behaving rather too true to its name, being rather sluggish and easy to catch. I was concerned about its safety as we have a high cat population locally, one of its not uncommon garden predators. Like other lizards the Slow worm does have a curious defence, the ability to lose its tail to escape predation using a mechanism known as ‘caudal autotomy’. By detaching a section of its body that then independently writhes vigorously it distracts its predator whilst it makes its more genteel escape. Perhaps it is this tail breaking trick that provides the ‘fragilis’ part of its Latin name. I have witnessed this phenomena and it is quite a sudden and amazing sight, with the tail demanding attention. Theseverance of its tail is a reflex achieved using a fracture plane (‘line of weakness’) in the caudal vertebrae. However it can only do this once and the new tail grows back significantly shorter than the original (Fuke, 2011), and can take several years (Bryant & Bellairs (1967). Despite the immediate advantage of surviving an attack, the tail loss has potential significant costs such as reduced locomotion and it has been shown to have a negative impact on reproductive success (Maginnis, 2006).
This all leaves me pondering the question, how does an individual Slow worm that can live 20 years plus determine the significance of every one of the many threats it will experience and decide on each occasion whether to play its one 'joker’.
Bryant, S.V. and Bellairs. A. (1967) Tail regeneration in the lizards Anguis fragilis and Lacerta dugesii. Journal of the Linnean Society of London, Zoology, 46(310): 297-305
Fuke, C. (2011) A study of a translocated population of Anguis Fragilis in Cornwall, UK. The Plymouth Student Scientist,4(2):181-221
Maginnis, T.L (2006) The costs of autotomy and regeneration in animals: a review and framework for future research. Behavioral Ecology, 17(5): 857-872.