For Pip Web­ster, it’s a nui­sance but but­ter­flies and cater­pil­lars thrive on it

Canal Boat - - This Month -

Net­tles are a nui­sance, es­pe­cially when try­ing to moor, but they are a home to some

Most of us know to our cost that both the round stem and the leaves of net­tles are armed with vi­cious stings. Brit­tle poi­son-filled hairs snap and act like small hy­po­der­mic nee­dles when just brushed against, re­leas­ing venom into the skin.

Ac­cord­ing to our an­ces­tors, the sting pro­tected you against sor­cery, but if you want to har­vest them safely, just pluck up your courage and ‘grasp the net­tle’.

Un­der firm pres­sure the hairs bend back harm­lessly or so it is claimed – I find my­self re­luc­tant to ex­per­i­ment.

You can then weave net­tles stems into fab­ric, and the iron-rich leaves, that lose their sting when cooked, can be con­sumed in net­tle soup and tea.

Sting­ing net­tles grow in ar­eas where phos­phate lev­els are high, as of­ten oc­curs in ar­eas pre­vi­ously dis­turbed by man. Most of the net­tles you will see grow­ing along the tow­path are the com­mon peren­nial type (Ur­tica dioica) that can reach about 1.5m high and bear clus­ters of tiny male and fe­male green­ish-white flow­ers on sep­a­rate plants.

Fe­male flow­ers are long and pen­du­lous while male flow­ers stick out at right-an­gles from the stem in the leaf ax­ils. Be­ing wind-pol­li­nated, the flow­ers have not had to evolve into flam­boy­ant blooms to at­tract in­sects.

The sting of the rarer an­nual net­tle (Ur­tica urens) is not quite so vi­cious. This smaller plant (30cm) has more rounded and deeply

toothed leaves than the com­mon or sting­ing net­tle and it is mo­noe­cious – both male and fe­male flow­ers are borne on the same plant. Tiny and green­ish, the flow­ers ap­pear in com­pact clus­ters in the leaf ax­ils. Both species flower from June through to au­tumn.

The tra­di­tional rem­edy for be­ing net­tled is to rub the af­fected area with a dock leaf – and I can vouch for the ef­fi­cacy. It is un­cer­tain whether the re­lief comes from a chem­i­cal com­po­nent or just from the cool­ing ef­fect of the sap re­leased from the crushed leaf. For­tu­nately docks of­ten grow in the same habi­tats as net­tles and any of the many species and hy­brids of dock found in this coun­try – they are no­to­ri­ously dif­fi­cult to dis­tin­guish – will do.

Sting­ing hairs evolved as a suc­cess­ful de­fence against graz­ing an­i­mals, so any in­sects liv­ing on the net­tles are also un­likely to end up in a her­bi­vore’s stom­ach. Small in­sects can move be­tween the spines on the net­tle with­out ac­ti­vat­ing the sting, so net­tles are the favoured food plant for the lar­vae of some of our most beau­ti­ful but­ter­flies, in­clud­ing the ‘net­tle fly’.

Bet­ter known today as the Red Ad­mi­ral (a cor­rup­tion of Red Ad­mirable), this hand­some but­ter­fly can be seen out at sea, al­beit on the wing.

A ma­jor in­flux of mi­grants from Africa and south­ern Europe ar­rive on our is­land in late May and June and work their way north­wards, join­ing the in­creas­ing num­ber of res­i­dent but­ter­flies that are able to sur­vive our milder win­ters. Vivid mark­ings in velvet black, scar­let and white dis­tin­guish one of the largest Bri­tish but­ter­flies.

Fe­males lay sin­gle small, green eggs on the up­per sur­face of young sting­ing net­tle leaves. Spiny cater­pil­lars hatch af­ter seven days; the black and yel­low-green colour forms both have yel­low mark­ings down each flank.

Each cater­pil­lar spins a small tent from a fold at the base of the leaf where it re­mains hid­den through­out its life, en­larg­ing its hide­out as it grows un­til pu­pat­ing, hang­ing in a net­tle tent.

The cater­pil­lars of the Red Ad­mi­ral’s cousins, the Pea­cock and Small Tor­toise­shell, are more gre­gar­i­ous and eas­ier to spot. The eggs of both of these species are laid in dense clus­ters on the un­der­side of leaves and the young, spiny cater­pil­lars feed in un­tidy webs spun over the net­tle tops be­fore dis­pers­ing when fully grown.

The pro­tec­tive web canopy is spun by the cater­pil­lars them­selves and is dis­taste­ful to preda­tory birds. So don’t slash all of those nasty net­tles down – some­body loves them.

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