|Life cycle: causes of death|
Grayling, Hipparchia semele, caught by the carnivorous Sundew, Drosera intermedia.
Carnivorous plants are an exceptional cause of death for most butterflies, because the plants are quite rare.
Even in the habitat where sundew is common, butterflies are not too often lured by the sticky droplets of the plant's tentacles.|
Hoge Veluwe, the Netherlands; 4 August 1990. Habitat
|Spiders as Predators of Butterflies|
Thymelicus lineola caught by Misumena vatia
Kell am See, Germany; 14 July 2008.
|Crab spiders hide in flowers, and their color often matches that of the flower to such a degree that they are very hard to spot. With the Small Tortoiseshell, I only saw the spider when I was pondering the tortoiseshell's curious posture... But crab spiders don't exclusively rely on crypsis and stealth. The white spider on the top right activally approached the skipper; this time unsuccesfully, as the skipper flew away unharmed...|
|This Small Tortoiseshell (Aglais urticae) was unfortunate enough to fly into the web of an Common Garden spider (Araneus diadematus). The spider rapidly wraps the butterfly in a silken cocoon. Its web thus becomes a larder... Marken, the Netherlands; 25 August 1991.|
But contacts with cobwebs need not be fatal, as I argue from the following photos. Compare the two Small Tortoiseshells shown here -
why do they look so different? It's the black on the hind wings that makes the difference. Normally, this black is partially covered
by blond hairs, as in the left photo. Now how did the butterfly in the right photo become afflicted by such blackish baldness?
I expect this to be the result of a non-fatal contact with a spider's web. When the Tortoiseshell frantically fluttered to escape, its hairs stuck to the sticky web - yet the butterfly got away well alive.
|Two detail from the right photo support my interpretation. First, the left photo below shows a detailed view of the wings. On the wings are parallel white stripes, due to a loss of scales. I think the scales stuck to the web - the lossed scales form a mirror image of the spiders web! Second, the photo right below shows there is some cobweb gossamer on the butterfly's antennae. So the butterfly got something in return for its lost scales...|
|Flies may not seem obvious predators of butterflies. However, Robberflies (fam. Asilidae) can be formidable hunters - there are even a few records of a large Robberfly catching small birds as prey! The following picture shows a medium-sized Robberfly, Stenopogon spec., with Colias spec. as prey.|
|Telltale Signs of Bird Attacks|
Two butterflies with similar colour pattern, and similar bird-attack marks. Coincidence? Of course, one can only speculate
about such anecdotal information, but what's wrong with a little speculation?
My hunch is that this colour pattern is functional in woodland area, the habitat of both species. Both species often rest on branches and leaves, in sunshine. There is often an extreme contrast between full sunshine and deep shadow, as can be seen in the photograph of the White Admiral. To a bird, the white band may every now and then appear as bright patches of sunlight, in effect hiding the butterfly.
Alternatively, when the butterfly is in full sight the white band may be the focus of attack, because of its visibility. This might explain why both butterflies survived the bird attacks from which they manifestly show the telltale signs.
Inachis io - Peacock
The Peacock is exuberantly coloured, so much so that one wonders whether there's special function to it. To many of us, the
most remarkable aspect are the four 'eyes', one on each wing. Did the bird attack an eye? Unlikely, in view of the symmetry
of the damage; the bird must have attacked the butterfly when it had its wings closed. But the butterfly opening its wings,
showing the full splendour of the eyes, might have been too much for the bird's gusto.
I once saw our cat at home touch a Peacock with wings closed. The butterfly opened its wings suddenly, and our cat jumped 1 meter backwards, from rest! A recent publication, Intimidating butterflies, confirms the protective effect of the Peacocks coloration.
The threadlike filaments at the hind wings of Hairstreaks would be similar to the antennae, in fact creating a 'false head'.
Because hairstreaks habitually rub their hind wings, the swinging filaments might atract a bird's attention. Here are two
photographs of a hairstreak, Satyrium acaciae and Satyrium spini. The white tip at the end of the filament certainly draws attention,
may be more so than the real antennae. The photograph right shows a sizable gap at the place of the filaments, consistent
with the idea that the filaments draw the bird's attention away from the more vital head...