My First Butterfly for 2014 – Milbert’s Tortoiseshell

On Friday, February 28th I saw my first butterfly of 2014 , in Lincoln Park, in the early afternoon of an incredibly beautiful, sunny, short sleeve day. The Milbert’s Tortoiseshell is one of the butterflies in the Nymphalini Tribe of the Nymphalid Family (Nymphalidae) butterflies.  This tribe of butterflies spends the winter in the adult stage, rather than as either egg, caterpillar (larva), or pupa.  In part because they are adults, on any day with weather conditions appropriate for butterfly flight, that is warm, sunny and calm, they can take a flight.  Friday, March 28th reportedly got up to 56 degrees F.  I’ve been told that this group of butterflies might fly any winter day that is sunny, calm and about 55 degrees, so we passed this threshold by one degree.

Of the two butterflies we are most likely to see here on a day like this, one, the Milbert’s Tortoiseshell has a gold band just inside from the outer edge of the wing, that is bordered by a more narrow dark band.  The second most likely butterfly at this time (though numbers vary greatly on different years), is the Mourning Cloak, which has a paler gold
band bordering the outer edge of the wing, and no dark border (the rest of the top side of the wing is dark brown).  Last year at about this time (March 9th) my first butterfly of the year was a Mourning Cloak, and that year was a big Mourning Cloak year.  As I have not gotten any Mourning Cloak reports yet from my butterfly chat groups, I don’t think this year will be such a big Mourning Cloak year.

The Milbert’s Tortoiseshell – Aglais milberti  (a.k.a. Nymphalis milberti) is one of 5 of our local, western Washington butterfly species that can lay their eggs on Stinging Nettles – Urtica dioica, and one of 3 local species that lays its eggs only on Stinging Nettles.  This makes Stinging Nettles our most critical local buttefly habitat plant, or more specifically “host plant”.  A “host plant” is a species that a butterfly can lay its eggs on and which its caterpillars can feed on to successfully reach the pupa, then adult stage.  We also have “nectar plants”, whose flowers butterflies will drink nectar from.  The young Stinging Nettle shoots were also out today.  The other 2 species that exclusively feed on Stinging Nettles as caterpillars, are the Red Admirable (a.k.a. Red Admiral) – Vanessa atalanta, and the Satyr Anglewing – Polygonia satyrus.  Each species has a distinctive pattern to how they feed on the nettles.  For the Milbert’s Tortoiseshell, its feeding signature starts with the fact that it is the only one of our nettle feeders that that lays its eggs in clusters.  The clusters have up to 900 individuals, and after hatching, young individuals make colonial webs that both many small caterpillars, and a lot of “frass” can be seen on.  “Frass” is a technical term for insect poop.  The other local nettle feeders lay eggs singly, and the caterpillar folds the nettle leaf in a characteristic manner, above or below the caterpillar, depending on the species, holding the leaf in its distinctive shape with the silk that caterpillars produce.

While we also can eat young Stinging Nettle shoots, they must be picked with a glove and cooked to avoid being stung by them, then they are a bit like spinach.  I also recommend that people don’t harvest them wholesale from busy parks where the butterfly moms are looking for safe places to lay their eggs, and other people might want to try a few.  To help the Stinging Nettle populations and the butteflies they support, if you recognise a non-native weed adjacent to the nettles, you can pull the weed and give the nettles a bit more room and less competition.

I am increasingly tamping down soil where I pull weeds, because the weeds are often adapted to a soil disturbance farming culture imported from Europe.  On the other hand, our natives are better adapted to undisturbed soils, especially those with the moss layer on top undisturbed, and the mosses grow better on undisturbed soils, that are more compact than airy.  Also just below the surface is a fungus layer that is invisible to us.  These fungi are critically important partners to our native plants, some of which may have specific partnerships between specific species.  The fungi also do better in soils that are not too aerated.  I theorize that the airy soils dry quicker, something that neither the moss on top, nor the fungus below the surface like.  The microscopic threads of the fungus mycelia may also spread more easily with fewer air pockets blocking their spread.


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One Response to My First Butterfly for 2014 – Milbert’s Tortoiseshell

  1. Stewart says:

    On yesterday’s (Monday, March, 24th) unusually warm, sunny day, that reportedly reached 68 degrees F, warmest this year, I also saw my first of the year Echo Azure (Celastrina echo) aka Spring Azure butterfly, my first of year Satyr Anglewing (Polygonia satyrus), and my first of the year Cabbage White – Pieris rapa, as well as my first of the year of 2 notable day-flying moths – “The Infant” – Archiearis / Brephos infans – in the Geometer / Inchworm Family – Geometridae, and the “Half-white Carpet Moth” – Mesoleuca gratulata – Geometridae The Echo Azure and the Cabbage White both winter in the pupa stage, so these were my first butterflies of the year that each hatched (“eclosed”) from their pupa. The Mourning Cloak, the Satry Anglewing, and the Milbert’s Tortoiseshell, that I’ve now seen this season, winter in the adult stage, and are capable of flying any day in the winter that is warm and sunny enough.

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