Monday, May 26, 2008

im not sacred of you any more

April is the cruellest month, sang T.S. Eliot (1922); Ja visst gör det ont när knoppar brister - Yes of course it hurts when buds are breaking (1935), lamented Karin Boye - (this was one in an unfortunate succession of stupid ideas that eventually provoked the authorities to step in and impress upon the poetry community that ideas were really not their forte, an opinion that most later poets have been very ready to submit to, especially the clever ones, the stupid ones aren't so easily led).

The obvious problem with spring isn't so much fear of one's own metaphorical rebirth as fear of the indifferent largesse of the sun, which gives nourishment and warmth to everything no matter what you think about it, to spiders as well as valerians.

But both are equally lovely! you say. And goes your heart with this? I reply suspiciously (in our imaginary conversation I'm allowed to throw in ridiculous pedantic quotations without anyone taking me properly to task) - Do you feel the loveliness of the baby spiders in just the same way you feel it of the flowers, or do you merely state your belief in it while really experiencing their presence as a sort of pustular rash?

Plants are for food, but we have a seasonal sense of rightness in which the plants are allowed their spring festival, and harvest comes later. At this time of year, animals should discreetly tweet and bleat and be sweet - not, for example, like the starlings who (with offensive publicity) were pecking a housemartin to death in the dust of the kerb.

So it's something of a shock to see, at this jouncing Chaucerian Maytime of the year (yes, apparently I can get away with talking like that, too...), that some of the fresh green hedgerows are - how can I see it differently? - disfigured by large black webby patches of something else...

The culprits - if one can attribute moral culpability to the act of having been born in a certain spot, which of course is what many humans believe - are the caterpillars of the spindle ermine moth Yponomeuta cagnagella; the food-plant, entirely stripped but just about recognizable from its stripy green bark, is Spindle-Tree (Euonymus europaeus).

Within their "tent" or "nursery" the caterpillars make a food factory of the shrub, consuming all greenery. Inside it's a busy, messy scene:

The webby material is presumably a creative use of excreta; those excessive sugars that present a logistical problem to the consumers of tender foliage; the sticky mass prevents birds and other insects from interfering.

When there's nothing left to eat of the spindle, the caterpillars have to make do with the surrounding foliage of field maple, hawthorn, and anything else they can stomach. Ermine-moth population explosions are intermittent and the shrubs recover the following year.


ADDENDUM (2009):

That last glib sentence was copied from some other Internet article, but it evidently isn't that simple. Every one of the plants that was covered in webs last year is covered in webs this year, too. Plus there seem to be a whole lot more of these webby patches, too (unless I'm just getting sharper at spotting them). We'll see what happens next. I'm keeping an eye on one plant which has green shoots growing out of the top of the web. I'm wondering if the caterpillars will be unwilling to expose themselves above their tent, and thus the spindle might be able to outgrow its predators.

ADDENDUM (2010):

Same again - the webs cover all the same places, and more too. Evidently the insect wasn't at all troubled by the coldest winter for thirty years.

ADDENDUM (2011):

Same again - more than before. Seems like a gradual build-up in the population. Plants in hedges seem to be more vulnerable than unpruned plants.

[with acknowledgement to Gösta Ågren]


A related species, the bird cherry ermine moth (Yponomeuta evonymella), can be even more spectacularly devastating. 

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At 7:59 am, Blogger Vincent said...

Oh yes. who gave us the idea that nature was pretty anyhow? the odd thing is that the young of mammals strike us as cute. Is it because we are so closely related to them? There is one bed of nettles in between two fields where I go to look at the peacock butterfly larvae. When they are big and plump they have a certain frightening beauty: black and spiny with white blobs randomly like skyscraper windows at night. But when they are younger and scrawny in their filthy webs, they are horrid: at least to us. Do the butterflies remember their larval life nostalgically? Why do they go back to the same patch each year to lay their eggs (to within a yard)?


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